Selecting and Planting Woody Plants PDF

HO-107 Selecting and Planting Woody Plants By Ray Maleike, Extension horticulture specialist, Washington State University. Adapted for Kentucky by Richard Durham, con- sumer horticulture Extension specialist and state Master Gardener coordinator, and William Fountain, Extension professor (ret.), Un...

HO-107 Selecting and Planting Woody Plants By Ray Maleike, Extension horticulture specialist, Washington State University. Adapted for Kentucky by Richard Durham, con- sumer horticulture Extension specialist and state Master Gardener coordinator, and William Fountain, Extension professor (ret.), University of Kentucky. Container plants are grown and sold in containers and are In this chapter: also available year-round. Field-potted plants are grown in a field, dug with or without Planting Trees and Shrubs 01 soil, and potted into containers filled with organic media Transplanting Established Plants 04 (substrate), field soil, or a combination of the two. Fertilizing 04 Watering 06 Woody Landscape Plant Problems 07 Winter Injury 10 Construction Damage 12 For More Information 14 W oody ornamental plants are key components of a well-designed landscape. Landscape plantings divide and define areas, add aesthetic and psycho- logical benefits, and increase a property’s environmental and economic value. There are many woody plants available for use in landscaping, bare-root bare-root packaged packaged so select carefully. Choose plants based on their ability to fulfill your purposes and grow well in your property’s environment. bare-root bare-root Install landscape plantings according to a plan, keeping two factors in mind: Use the right plants in each area to create your desired design effect. Place plants in the right environment with proper sun expo- sure, temperatures, soil pH, drainage, and water. Landscape plants last for many years. Making wise decisions for types of plants and giving plants proper growing condi- tions and care will help ensure that they remain a healthy and aesthetically pleasing part of your landscape. Planting Trees and Shrubs You can purchase trees and shrubs in a variety of ways (Figure 16.1): Bare-root (BR) plants have little or no soil around the roots. This method is common for deciduous plants and small bare-root bare-root evergreens shipped by mail duringpackaged packaged the cooler months. balled balledand and potted pottedoror bare-root bare-root Balled and burlapped (B&B) plants are dug with soil around the roots, with the root ball enclosed in burlap or a synthetic burlapped burlapped container-grown container-grown material, and are often available year-round. Figure 16.1. Types of nursery plants. CHAPTER 16 Selecting and Planting Woody Plants Planting Container plants Proper planting procedures are crucial to establishing a Dig a hole larger than the spread-out root system. healthy plant. Planting procedures depend on which type Always remove the container, even papier-mâché and of plant you choose (e.g., bare-root, balled and burlapped). peat pots. Instructions for the common types are given below. Understand the differences between container plants and those grown in native soils. Roots of container-grown plants Bare-root frequently circle the inside of the container. If this action is Cut back damaged roots with a clean cut. Then soak the not stopped, the plant will fail to become established in the roots in water for one to two hours. landscape. Roots of container-grown plants are also growing Dig a hole wider but not deeper than the root system. The in a substrate (artificial soil containing pine bark, compost root flair (where roots meet the trunk) should be no deeper or other materials), which has a different texture than soil. than about one inch below grade. Remove enough of the artificial mix to expose several inches Put the plant in the hole to the level where it was growing in of roots. You can do this by working your fingers into the the nursery (Figure 16.2). You can put a cone of soil under mix, resulting in the loose mix falling away from the roots. the plant for support and spread the roots on top of the cone. You do not need to remove all of the mix, but you should Backfill with native soil that is not amended. Tamp down remove as much as can be easily removed. the soil to remove air pockets. If the roots have begun to circle the inside of the container, Water thoroughly. try to unwind them so that they will radiate out away from the trunk. Balled and burlapped If the root mass is so dense that it is impossible to sepa- Dig a hole wider but not deeper than the root ball (Figure rate the roots, you will have to resort to cutting the roots. 16.3). Make several vertical slices into the root ball to stop the Remove the burlap or synthetic material from around the circling action. This is the least desirable corrective action ball along with all rope, string, or twine tying materials. but is often the only solution for plants that have become Place the ball in the planting hole with the top of the ball extremely pot-bound. even with the soil surface or slightly higher. Place the prepared root ball in the planting hole with the “Excavate, if necessary, to find the topmost root and ensure that surface of the container media level with the soil surface or it will be no deeper than one inch below grade. Sometimes the slightly higher. digging process results in balled and burlapped plants with Backfill with native soil that is not amended. Tamp down excess soil at the top of the ball. If needed, remove some of the the soil to remove air pockets. soil at the top of the ball. Water thoroughly. Backfill with native soil that is not amended. Tamp down the soil to remove air pockets. Water thoroughly. packed backfill correct incorrect packed backfill incorrect Figure 16.2. Planting depth for a bare-root tree or shrub. Figure 15.3. For B&B and container plants, the hole should be a mini- mum of two or three times as wide as the soil ball. 16-2  Selecting and Planting Woody Plants CHAPTER 16 Pruning Container soils have a bad habit of drying out much faster than the surrounding soil or backfill soil. Moisten both media Contrary to popular opinion, it is not a good idea to prune adequately to prevent new plants from being injured or dying of one-fourth to one-third of a tree or shrub’s branches to com- drought. However, be careful not to overwater. Average rainfall pensate for root loss when you plant it. However, light pruning in Kentucky is often adequate for woody plant growth once may be helpful in correcting problems. Follow these steps: the plant has been established. However, newly transplanted Remove dead or injured branches. trees and shrubs are not able to tolerate even brief periods with Remove interfering, rubbing, or crossed branches. inadequate rainfall. When the top five inches of soil/medium Remove branches forming narrow “V” crotches (multiple become dry, water the plant thoroughly, making sure to wet the or codominant leaders). Leave the other branch to become container and surrounding media to at least six to nine inches, the leader. and repeat as often as the soil becomes dry. Mulching newly established shrubs and trees helps prevent Staking moisture loss. Apply no more than two to three inches of mulch, A plant that is supported by a stake from the time it is small and ensure that mulch is pulled away about four inches from grows differently than an unstaked plant. It will be taller and the base of the trunk. thinner and have deformed xylem and less root growth. It may not be able to stand by itself. Bare-root trees generally need to be staked because they are tall and do not have the weight of firm soil around their roots to help stabilize them. If staking is not needed, don’t do it. If you do need to stake a plant in a windy area, follow these steps (Figure 16.4): Drive two or three stakes into firm ground outside the plant- ing hole. The line formed by the two stakes and the tree trunk should be parallel to the prevailing wind. Tie the two stakes to the trunk about two-thirds of the way up the trunk. Use a material that will not chafe or damage the bark. Allow some play in the line to allow slight swinging of the trunk. Gentle swaying of the trunk stimulates root growth on newly transplanted trees. Remove stakes as soon as possible after the roots are established and the plant is stabilized, typically after one growing season. Fertilizing Do not put fertilizer into planting holes and do not apply any fertilizer to the newly transplanted woody plant during the first growing season. Roots that come into contact with fertilizer particles may be damaged (burned). Root-stimulating products are also not needed, as their effectiveness is questionable. Watering A recently transplanted plant needs special attention through its first growing season. The nursery soil around a pot- ted or B&B plant may be radically different from the soil where it is planted, and water may not move readily between the two. Therefore, it is important to apply water to both the nursery soil and the surrounding soil during the establishment period. Roots grow only where there is moisture; unless both media are moist, roots may never grow out of the original nursery soil. Figure 16.4. Staking a newly planted tree. 16-3 CHAPTER 16 Selecting and Planting Woody Plants Transplanting Established Plants If plants are growing well in fertile, well-drained soil, they may not require regular fertilization. If plants are growing in Careful selection and placement of a plant should make areas with a lawn fertilization program, additional fertilization transplanting at a later date unnecessary. Occasionally you will probably be unnecessary for the woody plants. Fertilizers may need to move a plant. Plants often die after transplant- can be expensive, and many are manufactured using nonrenew- ing because of root damage or poor handling. Generally the able fossil fuels. If leaching and erosion occur, they can enter younger the plant and the more careful you are, the better your water supplies. Thus, remember these important tips: chance of success. Fertilize woody plants only when needed. Apply the correct amount of fertilizer at the right time of Timing the year. Place fertilizers where they will be available to the plant’s The best time to move evergreens is spring, followed by roots. early to mid-autumn. Move deciduous plants while they are dormant (usually from late fall to early spring, anytime the ground is not frozen). Determining the Need for Fertilizer Whether or not you carry out a yearly fertilizer program Preparation for landscape plants should depend on the inherent fertility of your soil, how well the plants are growing, and whether you If time allows, root-prune the plant a year or more before recycle nutrients (e.g., grass clippings or leaves). Very sandy digging. The fall before you plan to move the plant, divide the soils, for example, may lack sufficient clay and organic matter to circumference of the root area into six segments and prune hold nutrients and may be prone to low fertility. This situation every other segment by driving a sharp spade into the ground is not common in most areas of Kentucky. Landscape plants to the full length of its blade. (Make the circle of cuts slightly growing in such soils often exhibit nutrient deficiency symp- smaller than the size of the ball you’ll eventually dig.) New roots toms unless they are fertilized regularly. On the other hand, will grow at the cut edges. The following spring, prune the trees and shrubs in regularly fertilized turf areas may not need remaining segments. When you dig the plant for transplanting, supplemental nutrients. make the root ball larger than the root-pruned area to retain If plants are not doing well, fertilization may be helpful, but the maximum number of new roots. only after you determine the cause of the problem. Some pos- sible indicators of a need for fertilization are: Moving the Plant Smaller than normal leaves It is best to ball and burlap both deciduous and evergreen Light green or yellowish leaves (if the plant’s leaves normally plants before moving them to minimize damage. Dig a trench are dark green) around the plant, just beyond the spread of its branches (or just Shorter than normal annual shoot growth beyond your root- pruning cuts). Cut through woody roots, Dead twigs and branch tips but leave fibrous roots intact if possible. Use a garden fork to loosen the soil around the outer edge of the root ball to reduce However, these symptoms also may be caused by environ- its size and weight. mental, insect, disease, or other cultural problems. It is prudent Next, cut under the ball and tip it to the side so you can work to rule out any such causes before embarking on a fertilizer a sheet of plastic or burlap under it. Tip the ball from side to program. In Kentucky the most common cause of yellow foli- side carefully. Do not use the trunk of the plant as a lever to tip age is not lack of fertilizer but the attempt to grow acid-loving the root ball to prevent excessive damage. Wrap the ball tightly plants on alkaline soils. with plastic or burlap, lift the plant from the hole, and move it Research indicates that nitrogen may be the only nutrient to its new location. It is always best to move the plant by lifting that improves growth of woody landscape plants. In most cases, the root ball, not by lifting or dragging by the trunk. Unwrap potassium and phosphorus soil reserves are sufficient for woody the ball and plant it as you would a B&B plant. plants. Having your soil tested through the county Extension office or by a reputable laboratory can help you determine the levels of phosphorus and potassium. Very low readings of these Fertilizing two minerals may indicate the need to add these nutrients to Woody ornamental plants require moderate soil fertility your fertility program. A soil pH imbalance may also affect to thrive. High soil fertility stimulates excessive and possibly woody plant growth. For example, hollies become deficient undesirable growth. Low fertility is likely to make plants grow in iron when soils are alkaline. To the untrained eye, the yel- poorly and lack vigor. Plants stressed by low fertility are more low leaves seem nitrogen deficient, but the real issue is lack of susceptible to insect pests, diseases, and other problems, such available iron, often caused by incorrect soil pH. A soil test will as lack of hardiness. reveal soil pH. 16-4  Selecting and Planting Woody Plants CHAPTER 16 Fertilization is appropriate in some specific cases. For Once you know how much actual nitrogen you need, it’s example, it may help newly planted trees and shrubs reach their easy to calculate the amount of fertilizer to use. To apply three potential. Fertilizing also benefits trees and shrubs that have pounds of actual nitrogen per 1,000 square feet using a 21–7–14 been partly or completely defoliated by insects or disease, those fertilizer, divide the desired amount of nitrogen (three pounds that are stressed by digging or trenching in their root zones, per 1,000 square feet) by the percent of nitrogen in the formu- or those that may have suffered severe limb damage due to lation (21 percent, or 0.21). For example, 3 ÷ 0.21 = 14 pounds weather. Appropriate fertilizer application also may stimulate of fertilizer to achieve 3 pounds of nitrogen for a 1,000-square- recovery from winter injury. foot area. See Table 16.1 for approximate amounts based on other formulations. Types of Fertilizer The area beneath a tree usually is not exactly 1,000 square feet. To find the area beneath a tree or shrub, put four stakes in The three numbers on fertilizer packages refer to the percent the ground to form a square that encloses the dripline or extends of nitrogen (N), phosphorus (as phosphate, P2O5), and potas- beyond it (Figure 16.5). Measure the distance between the two sium (as potash, K2O), always in that order. Many fertilizer stakes along one side of the square and multiply this number by formulations are available, but since woody plants generally itself to get the area in square feet. Divide this number by 1,000, respond only to nitrogen, it is appropriate to use formulations then multiply the answer by the pounds of fertilizer needed per consisting only of nitrogen or ones in which nitrogen is pre- 1,000 square feet. The result is the amount of fertilizer needed dominant. Some examples are 16–8–8, 21–7–14, 20–10–5, for the tree. 21–0–0 (sulfate of ammonia), 33–0–0 (ammonium nitrate or For example: if one side of the square is 20 feet, then the area urea), and 45–0–0 (urea). Lawn fertilizers without weed killers under the tree is 20 feet by 20 feet, or 400 square feet. Four are acceptable for fertilizing woody landscape plants. hundred square feet divided by 1,000 square feet equals 0.4. If you need three pounds of actual nitrogen per 1,000 square feet, How Much Fertilizer to Apply and you want to use a 21–4–4 fertilizer, you need 14 pounds of Calculating by Area fertilizer per 1,000 square feet (from Table 16.1). Multiply 14 Deciduous, broadleaf evergreen, and needleleaf trees (coni- pounds times 0.4 (400 square feet) to get 5.6 pounds, or roughly fers) can be fertilized each year with one to three pounds of 6 pounds of 21–4–4. This is the amount to spread under the actual nitrogen per 1,000 square feet. If your soil is very poor or tree. The calculations for this example are: plants are not growing well, consider using the higher amount. 20 ft x 20 ft = 400 sq ft If plants are growing well and you know the soil is fairly fertile, 400 sq ft ÷ 1,000 sq ft = 0.4 use the lower end of the range or none at all. 3 lb N ÷ 0.21 = 14 lb (or read from Table 16.1) For flowering trees and shrubs, particularly crabapples, use 14 lb N x 0.4 = 5.6 lb fertilizer no more than two pounds of actual nitrogen per 1,000 square feet. Too much nitrogen may stimulate shoot growth at the expense of flowers. Table 16.1. Approximate amounts of fertilizer needed to provide stake 1, 2 or 3 pounds of actual nitrogen per 1,000 square feet. Amount of fertilizer to Type of apply per 1,000 sq ft fertilizer* 1 lb N 2 lb N 3 lb N 10–6–4 10 20 30 12–3–6 8 16 25 16–8–8 6 12 19 dripline 21–0–0 5 10 14 21–4–4 5 10 14 24–4–8 4.5 8.3 12.5 33–0–0 3 5 9 46–0–0 2 4 6.5 20’ Figure 16.5. Finding the area beneath a plant. *These are examples. Availability may vary by location. 16-5 CHAPTER 16 Selecting and Planting Woody Plants Calculating by plant size Fertilizing Hints You also can determine how much fertilizer to apply based Never put any type of herbicide-containing fertilizer (such on a plant’s trunk size, height, or spread. For example, shade as weed-and-feed products offered by various companies) trees with a trunk diameter of less than six inches (measured into planting holes, on the soil covering plant roots, or into at 54 inches (4.5 feet) above ground) should receive from soil near woody plants. one-eighth to one-third pound of nitrogen per inch of trunk Fertilizer applications do no good without moisture. If condi- diameter. Trees greater than six inches in diameter can receive tions are dry, irrigate soon after applying fertilizer. one-third to two-thirds of a pound of nitrogen per inch of Do not apply dry fertilizer to wet turf. trunk diameter. Fertilizers containing water-insoluble, organic nitrogen Flowering trees and large shrubs can receive from one-eigth sources may take three to eight weeks to break down to a to one-third of a pound of nitrogen per inch of stem diameter. usable form. Time applications accordingly. Shrubs often are fertilized according to their height or spread. Do not put fertilizer onto frozen soil. Precipitation and/or Use one-twentieth to one-tenth of a pound (about one to one snow melt will cause wasteful and environmentally hazard- and a half ounces) of nitrogen per foot of height or spread. ous runoff of the nutrients being applied. The following example shows how the amount of fertilizer to be applied to a shade tree with a diameter of eight inches can be calculated. Divide this number (2.4) by the percent nitrogen Watering expressed as a decimal (0.21 for 21–4–4 fertilizer). Thus: Watering landscape plants is one of the most misunderstood 1/3 (0.33) lb x 8 in = 2.4 lb actual nitrogen and challenging tasks facing gardeners. The average Kentucky 2.4 lb ÷ 0.21 = 11.4 lb of 21-4-4 climate generally supplies enough water for woody plants. Round off to 11 or 12 lb. However, our summer and fall seasons are often drought prone and windy. Plants may occasionally benefit from supplemental How to Apply Fertilizer irrigation during extreme droughts. Water-stressed landscape Apply fertilizer throughout a tree or shrub’s drip zone (the plants may be more susceptible to other problems such as area from the trunk to the edge of the canopy in Figure 16.5). insects, diseases, and winter injury. You can broadcast fertilizer over the soil surface and water it A good rule of thumb for watering is to fill the entire root zone in immediately. However, water-soluble nitrogen with a high with water and then allow the soil to dry partially before water- salt index applied to the soil surface may damage turf or other ing again. How much the soil should dry out between irrigations plants growing under the tree, and these plants may use the depends on plant species and size. For large trees and shrubs, allow nitrogen before it reaches the tree’s roots. Placing fertilizer in the top several inches of soil to dry before rewatering. Water small, holes or pounding in spikes is not recommended as the fertil- newly established, or extremely shallow-rooted plants before very izer is placed below many of the roots. On steep slopes, it may much soil drying occurs. Become familiar with how long it takes be necessary to place fertilizer into the soil to keep it from to completely moisten the root zone of various plants in your entering streams. landscape and how deeply the soil can dry before plants begin to show signs of stress. Some situations may require more frequent watering than When to Fertilize the rest of your landscape. Check these areas and water them Research indicates the most effective time for established more often. For example: deciduous plants is late fall. For trees or shrubs planted in turf Shrubs and groundcovers near house foundations, under areas, it may be better to split the amount into several applica- eaves, or in hot afternoon exposures may receive little water tions to avoid burning the grass. If you apply fertilizer during from natural precipitation or may transpire water rapidly, so winter when turf is likely to be dormant, it may not be necessary they may be stressed during hot summer days. to split the application. Mounds or berms have much more soil surface exposed to In Kentucky, where most trees and shrubs grow among cool- evaporation than does the natural soil profile, so they dry season turfgrasses (Kentucky bluegrass and fescue), fall applica- out more quickly. Runoff is also more rapid. tions are best to avoid excessive growth of turfgrass in spring. Some plants, such as rhododendrons, azaleas, and ferns, Fertilizing landscape plants with high-nitrogen fertilizer demand more moisture or have shallow roots that dry out after mid-July is not recommended. It may stimulate growth quickly during warm, sunny weather. that will not have time to harden off before fall; consequently, the plant may be damaged by winter freezes. Wait until plants Many native woody plants that are drought tolerant should are dormant, between Thanksgiving and New Year’s Day. not be watered during the summer once they are established, and some may be damaged by summer moisture. 16-6  Selecting and Planting Woody Plants CHAPTER 16 How to Water Fertilizer does absolutely no good unless it is dissolved in water. Always water after applying fertilizer if it doesn’t rain Water trees and shrubs just under and outside their dripline at least a half inch over the following six hours. or outer edge. For foundation or border plantings, water the Conserve water where possible. Clean water is a valuable entire area. resource that should not be wasted. Hoses, soaker hoses, or various kinds of sprinklers are Winter drought conditions are uncommon in Kentucky, but common watering methods. For deep-rooted trees, try a root trees still require water in winter. If you need to apply water needle or fertilizer-feeding needle (without the fertilizer) for in winter, make sure that the soil is not frozen, which would deep watering. This is a tedious process, but it gets water into cause the water to run off. areas of the root zone that may take a long time to reach with a sprinkler. In soils that are slow to accept water, try building a dish-like Woody Landscape Plant Problems or berm-enclosed area around the base of newly planted trees If cared for properly, landscape plants can live a long, healthy or shrubs. Fill this area with water. After the first growing sea- life. However, they can suffer damage from a wide variety of son, remove the basin rims to avoid directing too much water causes. Microorganisms cause problems such as root rots and into the root zone. foliage diseases. Insects also cause injury. However, most plant problems are due to adverse weather or cultural conditions that Watering Container Plants stress the plant. These conditions include freezing, drought, Plants in containers need special care because both the overwatering, and improper use of fertilizers. Tree thinning volume of soil and amount of available water in containers are and construction activities such as grading also contribute to limited. Water these plants more often than those in the ground. stress by compacting soil, submerging roots, and injuring plants The frequency and amount of water needed depend on the with equipment. medium, exposure to sun or wind, temperature, humidity, size, Symptoms of plant damage resulting from stress sometimes and type of plant. Plants growing in plastic or ceramic contain- do not show immediately. In fact, they may not be obvious for ers need water less often than those in porous fiber or clay pots. years. Symptoms may result from the accumulation of several Water when the medium surface feels dry. If a container stress conditions. In addition, the older a plant is, the less likely completely dries out, you may need to soak it to rewet the soil. it is to successfully adapt to change or difficult conditions. A potted plant that uses a lot of water, such as a fuchsia, or one that is pot-bound may need to be watered daily or even Root Problems several times a day during dry weather. For most container- The root systems of partially to fully mature trees and shrubs grown plants, however, a thorough watering every two to three normally extend far beyond the plant’s dripline. The rooting days is sufficient. depth normally is fairly shallow—usually only to the depth of Be careful not to keep the root system soaking wet, and do good soil. Sometimes roots grow very close to or above the soil not allow the pot to sit in water. Disease problems occur more surface. This condition may be caused by any of the following: often when soil is constantly wet. A high water table A hard soil layer (hardpan) just beneath the surface Watering Hints Shallow, frequent watering Remember that most woody plants of native origin to Kentucky will require extra supplemental water as they Several root problems are discussed in this chapter. Keep are established, but normal rainfall will usually suffice once in mind that the symptoms of these problems may show up in plants are established. other plant parts, especially leaves. A quick, light watering does not wet the entire root zone properly. Frequent, shallow watering leads to shallow roots. Trunk Girdling (Strangling) Roots Shallow roots suffer more stress during drought or hot Symptoms—This problem eventually limits water and nutrient weather and may freeze in very cold weather. transport up the trunk, causing slow deterioration of the plant. You can water any time of the day, but it is more efficient to The plant is stressed and top growth diminishes. water at night, when evaporation losses are less. However, Causes—It can result from impurities (such as sheetrock or sprinkled water on surrounding plants may promote disease. lumber) in the soil; twisting the plant during the planting pro- Early morning watering is better in this situation. cess; and failing to spread roots properly during transplanting. Too much water is as bad as or worse than too little. Excess Remedies—Remove debris and foreign materials from the water can run off, leach nutrients, and promote root diseases. soil before planting. Prune girdling roots and spread roots Do not apply water faster than the soil can absorb it. when planting. 16-7 CHAPTER 16 Selecting and Planting Woody Plants Circling Roots Compacted Soil Symptoms—General decline of plant vigor is noted over a Symptoms—A decline in growth develops from the top down. period of time. Cause—Soil is compacted or roots are damaged by foot or Cause—The plant remained in its container too long at some machine traffic after the plant is in the ground. This is especially stage of development (not necessarily the last). serious when traffic occurs on wet soils. Remedy—Spread the roots, butterfly the root ball, or slash and Remedy—Buffer the area with a thick (two to three inches) spread the roots when you plant. layer of organic mulch. Direct traffic away from plants. Protecting the critical root zone of established plants prior to Kinked Roots, One-Sided Root System construction is less expensive and more effective than mitiga- Symptoms—General decline of plant vigor is noted over a tion of soil compaction after it has occurred. period of time. Causes—Improper production methods, jamming the plant in Plastic Bag, Synthetic Burlap or Other Materials Left on the Plant’s the pot or planting hole, or dragging with a mechanical planter Root System (J-shaped roots) can create this problem. Symptoms—Wilting, stunted growth and eventual death will Remedy—Cut off kinked roots and carefully spread and occur. straighten the remaining roots when planting. Cause—Plant was not removed from pot before planting, or synthetic burlap or twine remained after planting. Root Rots Remedy—Take the pot and other materials off the plant before Symptoms—Roots are mushy, brown, and partially to totally planting. decayed. The plant usually wilts and partially or totally dies. Causes—Variable causes are possible, depending on suscep- Stem Problems tibility of the plant to disease organisms, poor soil aeration, amended backfill soil, inadequate drainage, and overwatering. Stem maladies usually arise from improper care or stress. Remedies—Increase downward and lateral drainage. Plant Heart Rot higher in raised beds. Plant flood-tolerant species or resistant Symptoms—Heartwood or other internal portions of the varieties. Do not amend backfill when planting. Monitor trunk or branches decays. watering. Causes—Improper pruning, broken branches, storm damage, Suffocated Roots wounded stems, or root damage can lead to the problem. Symptoms—Tree or shrub trunk shows no buttressing or flar- Remedies—Filling cavities and using pruning paint is of no ing out at the point where it enters the soil. Leaf and branch value and can actually increase the rate of decay. If decay is in growth declines from the top down. advanced stages, remove the tree for safety. Avoid problems by Causes—The addition of fill soil, planting too deep, plants using proper pruning techniques. that were grown in the nursery too deep in the soil ball, or Stem Wounds, Cankers, or Girdling of Trunk and Branches paving around the plant’s base decreases the air supply to roots Symptoms—Bark wounds are visible. and changes water movement patterns. Susceptibility varies Causes—Damage can be caused by rope left on after planting, with species. careless use of lawn mowers or weed trimmers, or staking ties Remedies—Remove the excess soil covering the roots of or wires left on too long. established plants. Replant newly installed tress and shrubs at Remedies—Remove all ties when planting. Stay away from the correct depth. Improve the drainage. Consult an arborist plant stems and trunks with mowing and weed-cutting equip- about whether an air well around the trunk base of mature, ment. If damage occurs, cut away the loose bark in a rounded established trees might help. ellipse. Painting or spraying the wounded area provides no Cut Roots benefit and may even be detrimental. Symptoms—Death or decline in growth occurs from the top Fork Pockets, Bark Inclusions, or Narrow Crotches that May Split of the plant downward. Cause—Two or more branches compete to be the central Cause—Digging trenches within the plant’s root zone severs leader (codominant leaders). the roots. Remedy—Prune out all but one of the leaders if the tree is Remedies—Avoid cutting large roots; tunnel under roots young. If the tree is old, consider subordinating the weaker where possible. Cut back damaged roots cleanly. Water the branch, cabling, or cabling and bracing the competing limbs. plant. Fertilization is of questionable benefit and often increases Failure to mitigate the problem may result in branch failure and decay in cut roots. the potential for damage. 16-8  Selecting and Planting Woody Plants CHAPTER 16 Bark Scald, Sunscald, or Southwest Disease Remedies—Determine the cause, then take appropriate Symptoms—Bark is dead, usually on the south or southwest action. Watering may help if the problem is not due to poor side of the trunk. drainage. Causes—Hot sun, or alternate freezing and thawing of bark, Flooding can be the cause. Newly transplanted and young trees are very Symptoms—Plant is wilted or droopy. susceptible. Cause—Too much water limits available oxygen to roots, Remedies—Shade the southwest side of the trunk with a loose thereby reducing or stopping water uptake. layer of plastic window screen. Wrapping is of questionable Remedies—Improve drainage. Decrease water supply. Plant benefit on mature trees, although it may be helpful for newly on a berm or raised bed. planted trees. If you do wrap a trunk, use wrap that is a light color (to reflect sunlight) and woven (to allow air passage). If Plugged Vascular System damage occurs, cut loose bark back to firmly attached bark. Symptom—Plant wilts. Remove all wraps after the danger of winter freezes has passed. Cause—Diseases such as verticillium wilt can be the culprit. Remedy—Determine the cause and take appropriate action Graft Failure (e.g., apply a registered fungicide or use resistant plants). Symptoms—Large overgrowths appear above or below a graft union, or the plant breaks cleanly at the graft union. Leaves Salt Damage change color early in autumn. Symptoms—Marginal to interveinal chlorosis or necrosis Cause—The grafted scion and stock are incompatible. occurs, and rootlets are brown instead of white. In containers, Remedy—Purchase plants rooted from cuttings (not grafted). the soil surface or edge of the pot may be covered with white Avoid stock–scion combinations with known problems. salt deposits. Cause—Soil can accumulate excessive salts from fertilizers, manures, and deicing materials. This problem may be more Leaf Problems prevalent in containers than in gardens. It also is more com- Symptoms of stem and root maladies may show up in leaves. mon in arid areas than in regions where winter precipitation Many insects and diseases also affect leaves. leaches away excess salts. Remedy—Leach salts from soil by applying irrigation water Wilted Leaves in excess of the water-holding capacity of the soil. See Chapter If a plant is wilted, the leaves are losing water faster than it 4, Soils and Fertility, for more information. can be supplied by the roots. Plants vary in how much water they need. The exact cause of wilting must be determined by Yellow (Chlorotic) Leaves observing symptoms and the plant’s environment. Some pos- Nitrogen Deficiency sibilities are discussed below. Symptoms—Plant shows overall yellowing, with older leaves Drought or Lack of Water changing first. Symptoms—Soft growth wilts. Extended periods of dryness Cause—Not enough nitrogen is available in the soil. can cause early leaf drop, marginal and interveinal chlorosis Remedy—Fertilize with a nitrogen fertilizer. (yellowing), and necrosis (tissue death). High pH Cause—There is not enough water in the soil. Symptoms—Interveinal chlorosis occurs, appearing in newer Remedies—Supply water. Increase soil water-holding capacity. leaves first. Chlorotic regions may die. Mulch. Plant drought-tolerant plants. Cause—Alkaline soil may cause iron and/or manganese to High Temperature and Bright Sunlight become unavailable. Symptoms—Leaf browning and blotch necrosis occur. Remedies—Decrease soil pH with elemental sulfur, iron sul- Cause—Plants have been exposed to hot sun. fate, or ammonium-based fertilizers. Spray the plant or drench Remedies—Shade the plant. Use plants tolerant to heat and the root system with iron or manganese chelate as a temporary low humidity. Periodically syringe leaves with water for tem- measure. This will cause the plant to become greener, but does porary cooling. not improve the vigor or health of the plant, only the aesthetics. Lack of Roots Other Causes Symptoms—Wilting, early leaf drop, chlorosis, necrosis, poor Chlorosis also may be caused by drought, misuse of herbi- growth, and death are common symptoms.. cides (see “Herbicide Damage” section of this chapter), bright Causes—Rot or decay (caused by poor drainage), trenching, sunlight, or natural leaf maturity. Some plants naturally have transplanting, or insects (e.g., root weevils) can be the cause. variegated or light green leaves. 16-9 CHAPTER 16 Selecting and Planting Woody Plants Herbicide Damage Bright, sunny days with frozen soil Herbicides have specific toxicities to weeds, but also may Depth to which the soil freezes damage desirable plants. Almost all herbicide damage results Drying winds from misuse. Few problems arise when label directions are fol- Low humidity lowed closely. The key is to read the label and think. Lack of snow cover, mulch, or other insulating materials If many plants in one area show symptoms, suspect herbicide Site Influences damage. Severity and type of damage depend on the type of herbicide, amount applied, plant species, and stage of growth Distance from a large body of water at the time of application. Solid fences, hedges, or barriers that trap cold air and create Some herbicides act as plant hormones, causing twisted and frost pockets distorted growth. Others inhibit photosynthesis and chloro- Soil moisture availability before a freeze phyll production, causing chlorosis. Soil conditions, soil type, and mulch Table 16.2 lists some common herbicides and their possible Raised beds or containers effects. Windbreaks Even if only part of the root system is affected by an herbicide, Plant damage may spiral up the plant. Know where the root zones of Genetic hardiness of the species your desirable plants are. Take special care when applying turf Genetic adaptation to a different geographic area (ecotype) herbicides for broadleaf weed control within the root zones of Differences in hardiness of different plant tissues desirable plants. How well the plant is established Dormant oil used for insect and mite control may damage Condition of the plant, including dormant or partly dormant needled evergreens if applied during freezing weather or if not well state or stress from drought, fertilizer burn, or insect damage mixed. Dormant oil will also wash off the blue color of Colorado Growth stage of the plant blue spruce (Picea pungens) but does not otherwise harm Protective reactions of the plant (e.g., leaf drop or leaf rolling) the plant. Why Winter Injury Happens Winter Injury Winter injury to landscape plants occurs in various ways. Causes By understanding how plants react to winter temperatures, you sometimes can predict the type and extent of damage that Winter injury may be caused by a complex combina- might occur and take actions to protect your plants. tion of circumstances rather than a single factor. Factors The limits of winter hardiness are controlled genetically and involved include: vary greatly among species and even among plants within the Weather same species. For example, Douglas firs (Pseudotsuga menzie- sii) that evolved in the Rocky Mountains are hardier than those Deviation from normal minimum winter temperatures that evolved in the Cascades (Pacific Northwest). Likewise, Dramatic fluctuations in winter temperatures flowering dogwoods (Cornus florida) from New York are Length of a severe cold period hardier than those from Florida or Georgia, even though they Time of year when a cold period occurs are the same species. Table 16.2. Herbicide effects on plants. Herbicide Damage Symptoms Broadleaf plants: Chlorosis or necrosis of tips, margins, or interveinal areas. Sometimes more Dichlobenil (Casoron) severe on leaves exposed to the afternoon sun. Conifers: needle tip chlorosis or necrosis. Broadleaf plants: Twisted, distorted leaves and stems. Bark blistering on London plane trees. Phenoxy compounds (2,4-D, MCPP, triclopyr) Grapes, Mahonia, and tomatoes are very sensitive. Conifers: Misshapen, distorted needles. Note: These herbicides are particularly susceptible to drift. Broadleaf plants: Twisted, distorted new growth, chlorosis, necrosis, death of trunk tissue. Dicamba (Banvel) Conifers: Distorted, twisted needles; needle necrosis from the base to the tip; club-shaped growth. Broadleaf plants: Death of part or the entire plant, strap-shaped new leaves, purplish cast to Glyphosate (Roundup) plant. Conifers: None noted. Broadleaf plants: Chlorosis, leaf tip to margin to interveinal; may become necrotic. Conifers: Triazines, atrazine (AAtrex), simazine (Princep) Needle tip chlorosis. May cause plant damage or death if applied over the (chemical sterilants) root system of desir- Long-term residuals able plants. 16-10  Selecting and Planting Woody Plants CHAPTER 16 Plants native to a geographic region have evolved in response is much hardier than roots, so the top of the plant may not be to the area’s climate and weather patterns. The hardiest plants damaged. It may leaf out in spring and then, for no apparent survive and produce offspring, passing on their genetic hardi- reason, wither and die. Check the roots to see whether this type ness. Thus, plants native to an area are usually able to survive of injury has occurred. Dead roots usually are brown or black winters characteristic of that area. and may be soft. Live roots have a white growing tip and are Many landscape plants are introduced (often called exotics). white to greenish under their bark. They may be adapted to completely different environments You can reduce this type of damage by putting containerized than they encounter here. Exotic or introduced plants often plants in a protected area such as a cool garage or greenhouse respond differently to local climatic patterns than native plants. during winter. It may be sufficient to bury containers in sawdust, Cold hardiness develops each fall in an organized pattern as ground bark, or soil to insulate roots during winter. physiological changes take place in a plant. These changes are driven by the arrival of shorter days and cooler temperatures. Scald of Leaves by Sun and Wind The rate of acclimation varies by species and the extent of During periods of severe cold combined with bright sun- cooling. If fall temperatures remain warm, plants may fail to shine, the leaves of some broadleaf evergreens deacclimate. adequately acclimate to cold. When the sun sets, the deacclimated leaf tissue freezes. Ice Deacclimation or dehardening is the loss of hardiness. It is forms in the cells, rupturing their membranes and walls, and a plant’s response to warming temperatures in late winter and the cells die. early spring. Typically, deacclimation is gradual, but it can be Damage usually is worse on leaves exposed to the afternoon rapid during an extended warm period. Some species, but not sun (on the south or southwest side of the plant). Plants vary in all, require a chilling requirement to exit dormancy. The chill- their susceptibility to sunscald. ing requirement is satisfied when the plant accumulates a set Winter wind and sun, alone or in combination, can damage amount of exposure to low, non-freezing temperatures (45°F) evergreens by causing them to transpire (lose water) through during dormancy. Only after this requirement is met can plants their leaves or needles. The water is not replaced because deacclimate. The chilling requirement of a given species will roots cannot take in water from cold or frozen soil. Affected vary depending on where it originated. leaves turn brown, starting at the edges or tips and progressing Cold temperature damage may occur at any time, depend- between the veins or down the needles. ing on the severity of the cold and the stage of hardiness of the Prevent these maladies by protecting plants from wind or plant. Damage is most common during: shading them. A sudden, dramatic drop in temperature following a rela- tively warm fall. Plants may not yet be acclimated to cold. Sunscald of Bark Very cold midwinter temperatures. Even after a good accli- Trees can suffer sunscald on sunny winter days. Damage mation period, marginally hardy plants may suffer damage. usually occurs on a trunk’s exposed southwest side. Sunscald A sudden, severe temperature drop after a warm spell is more prevalent on stressed, recently transplanted, smooth- in late winter or early spring. Plants may have started to barked, or thin-barked trees. It occurs when bark and cambial deacclimate. tissues deacclimate and do not reacclimate quickly enough A late freeze after growth starts in the spring. New, soft when the sun sets and the temperature drops abruptly. The growth usually cannot tolerate frost. Plants that bloom or result is tissue damage or death. Sun-scalded bark often cracks start to grow early in the season, such as flowering cherries, open or separates from the tree without splitting. magnolias, photinia, and some very early-blooming rhodo- To prevent sunscald, wrap trunks of recently transplanted dendrons, are susceptible to damage from spring freezes. trees and those that were stressed during the growing season. Use light-colored wrapping and wrap from the soil line to the first set of branches. Leave the material on for the first winter Types of Winter Injury and remove it at the beginning of the first growing season. Bud and Stem Damage Buds and stems die or are damaged if a plant is not genetically Leaf Droop and Leaf Rolling hardy or has deacclimated. Some buds or tissues may be killed, Drooping and rolling of leaves are protective reactions to while others remain healthy. On some tender hydrangeas, cold cold. They reduce the amount of leaf surface exposed to cold may partially or completely kill flower buds. Thus, there may and drying winds. Leaves return to normal as temperatures be fewer flowers than normal on these plants after a colder- warm. On some rhododendron varieties, the leaves fold back than-normal winter. flat against the stems or roll up tightly. If leaves are not killed by extreme cold, the plant will return to normal when the Frozen Roots weather improves. The medium in an aboveground container or B&B tree may freeze, killing a plant’s roots. In most plants, stem tissue 16-11 CHAPTER 16 Selecting and Planting Woody Plants Limb and Branch Breakage Check the plant in several places: at the twigs, farther down Branches may break because of heavy snow or ice loading. the branches, and at the crown or soil line. If the outer twigs Prune the broken portion back to an undamaged branch or the are dead, move toward the trunk until you find live tissue; older main trunk. On large branches, make pruning cuts just outside wood may be hardier than young wood. the branch collar. Once you determine the extent of the damage consider the following steps: Delayed Symptoms Prune out and remove dead and severely damaged wood. The results of winter injury sometimes take months or Prune properly, leaving no stubs. Prune back to live, green, years to appear. Sometimes, leaves live until their reserves are healthy wood: a bud, live stem, or trunk. Do not prune live depleted, which occurs slowly in cool weather but rapidly when wood. the weather suddenly warms. Water properly during the following growing season. Pay Graft unions may be sensitive to damage from cold. Only a particular attention to plants beneath eaves. portion of the graft may be injured. It may function for years If the soil lacks adequate amounts of basic plant nutrients, until another kind of stress causes it to fail. add fertilizer. If growth appears normal, fertilize only lightly, Winter-damaged tissue may allow disease organisms and if at all. insects to enter. Again, these problems may not be evident Use a loose, organic mulch to maintain soil moisture and for years. protect the upper roots from temperature extremes. Root systems, especially of shallow-rooted plants such as On damaged fruit trees, remove as much developing fruit rhododendrons and blueberries, may be injured by cold. When as possible to allow the plant to recover and rebuild reserves damaged roots fail, the plant’s top starts to die. rather than produce fruit. Preventing Winter Injury In short, the best thing you can do for a winter-injured plant is to avoid further stress during the coming season by giving it Select plants adapted to your local climate and soil special attention and care. conditions. If possible, place evergreen plants in areas that minimize their exposure to sun and wind. Otherwise, provide a wind- Construction Damage break or shading during winter. When clearing a building site, developers often leave large, In the fall, wrap the trunks of young and recently trans- well-established trees to enhance the property’s aesthetic value. planted trees with a white or light-colored woven wrap. Often, however, these trees soon decline. They may exhibit Keep plants healthy by proper planting, fertilizing, watering, stunted leaves or needles, short internodes, or dead branches and pest control. and foliage throughout the plant. Do not fertilize, prune, or water heavily late in the growing season. Doing so can encourage late-season growth that may Change of Grade not acclimate well. When preparing a building site, developers often move soil, Protect shrubs from heavy snow accumulation. sometimes to level areas that once were sloping, or to develop Water landscape plants, especially evergreens, during fall and slopes where the soil was originally level. If trees are left stand- early winter dry spells. Pay close attention to plants under ing, soil may be added over their roots. Reducing the soil grade overhangs or in other places where they may not receive rain removes tree roots along with the soil. These changes can cause or snow. significant damage and even death of trees. Raising the grade can suffocate roots. The damage may What to Do for Winter-injured Plants depend on the kind of tree, the depth of the soil fill, and the tex- Don’t do anything until new growth begins on live wood, ture of the fill. Most trees are adversely affected if several inches usually in late spring. It is easier to determine which stems of soil fill are placed over their roots. Sandy or gravelly fills are actually are dead after growth begins. Sometimes, faded green less damaging than heavier textured soils such as silt or clay. branches begin to regrow and do not die. Even if leaves are dead, Placing asphalt paving or concrete over a root system can stems and vegetative buds still may be alive. have the same suffocating effect as raising the grade around a Before pruning a sad-looking plant to almost nothing or tree. These processes usually cause significant root damage. pulling it out altogether, check for signs of life. Scrape the bark Lowering the grade also can be detrimental. Most feeder away with a fingernail or make a shallow cut just under the bark roots, which supply the tree with water and nutrients, are with a pocketknife. Live branches are bright green or white located in the top six to eight inches of soil. Removing soil just beneath the bark. Dead branches are brown and may look removes or injures many of these roots. If enough large roots water soaked. are lost, the tree may lack anchorage and fall. Also, damaged or broken roots sometimes rot back to and into the stem. 16-12  Selecting and Planting Woody Plants CHAPTER 16 Grade changes also may affect the water table, either lower- Care after Construction ing or raising it in response to soil changes. Also, paved areas may direct more or less water into a tree’s root zone. The larger Care for Damaged Trees and older the tree, the more difficult the recovery can be. Usually the owner of a new house or other structure is not involved in land- clearing and construction decisions and has Soil Compaction no idea what changes have taken place. Often, developers and Heavy equipment or repeated human or animal traffic builders do not take proper precautions with regard to trees. compacts soil. Compacted soil is less open to air and water Thus, the owner may not be aware of damage until trees begin movement, thus creating adverse conditions for root growth. to show signs of stress. By that time, chances of saving them Sandy soils or soils high in organic matter tend to compact less may be slim. than heavy, clay soils. Even with prompt treatment, severely damaged trees may die. The sooner treatment is begun, the better the chance of Mechanical Injury recovery. Water and fertilize damaged and possibly damaged Bulldozers and other equipment may gouge the bark off trees and shrubs properly. In this case, water is much more a tree’s trunk or root crown and can damage roots simply by important than fertilizer. If you fertilize, use a complete fertilizer moving over them. If bark is completely knocked off around containing nitrogen and phosphorus in about equal propor- its trunk, a tree will die. In less severe cases, decay organisms tions. Late fall and early winter are the best time for fertilizer may enter wounds. Large, untreated stem wounds eventually application to damaged trees. See “Fertilizing” section earlier can cause internal rot, sometimes called heart rot. in this chapter for more information. Digging trenches for foundations, pipes, and cables causes If trees are wounded, remove loose and dead bark from serious root loss and damage. The closer the trench to a tree, around the wounded area and shape the wound margin with a the more severe its effect will be. Damaged trees may die or fall. sharp knife. If callus tissue (the ridge of tissue that forms around and eventually covers a wound) has started to form, do not cut Tree Thinning into it. Wound dressing (wound paint) serves no useful purpose Sometimes builders or homeowners remove selected trees and may be detrimental. to create space, decrease shade, or give desirable trees more Pruning—particularly excessive pruning—diverts carbo- room. When trees are thinned, the remaining trees are exposed hydrate production to a plant’s top (shoots) at the expense of to more wind. They may suffer damage ranging from a few bro- root growth. Thus, pruning is not a good idea if there is root ken limbs to completely blowing over. A stand’s vulnerability loss. Otherwise, prune dead and damaged wood back to sound increases when the larger trees (with large crowns) are taken wood. Use thinning cuts. out or blow down. Remove dead trees. If live trees are a hazard, remove or cable them. Have ISA-certified arborists do all pruning and removal Preventing or Lessening Construction Damage of large trees. Before land clearing and construction begin, mark off the dimensions of the building, driveway, and other major construc- Care for Protected Trees tion areas. Decide which trees to save (or transplant) based on Even with proper land clearing and building, good tree care their proximity to the construction area, health, age, and species. following construction is vital to continued life and growth Then build a barrier to keep equipment away from the remain- of trees and large shrubs. Proper watering and fertilizing are ing trees. If trenching near desirable trees is necessary, tunnel necessary. Additional pruning may be necessary to direct future under, rather than through, the root system. If you must raise growth. Keep trees under observation for 8 to 10 years after the grade around a desired tree, construct a dry well around it. construction and treat promptly if needed. Consult an ISA-certified arborist for advice. 16-13 CHAPTER 16 Selecting and Planting Woody Plants For More Information Dirr, Michael A. Viburnums: Flowering Shrubs for Every Season. Portland, OR: Timber Press, 2007. Hundreds of species of trees, shrubs, vines, and groundcov- Harris, R.W., J.R. Clark, and N.P. Matheny. Arboriculture: ers can be used as landscape ornamentals, specimen plants, Integrated Management of Landscape Trees, Shrubs and container plants, or in countless other ways. A wealth of Vines, 4th edition. Englewood Cliffs, NJ: Prentice Hall, 2003. information is available to help you better understand specific Hensley, D.L. Professional Landscape Management, 2nd edi- plants and how to use them. Check with local bookstores or ask tion. Champaign, IL: Stipes Publishing, 2004. your county Extension service for publications about growing Shigo, A.L. Modern Arboriculture. Durham, NH: Shigo and plants in your area. Trees, Associates, 1991. Shigo, A.L. A New Tree Biology. Durham, NH: Shigo and Trees, UK Extension Publications Associates, 1991. Planting Balled and Burlapped Trees and Shrubs in Your Urban, James. Up by Roots: Healthy Soils in the Built Landscape (HO-91) Environment. International Society of Arboriculture, 2008. Botanical Diversity in the Landscape (HO-92) Watson, G.W., and E.B. Himelick. Principles and Practices of Trees and Compacted Soils (HO-93) Planting Trees and Shrubs. Urbana, IL: International Society Trees with Minimal Insect and Disease Problems for Kentucky of Arboriculture, 1997. Landscapes (HO-94) Recognizing Trees of Significance (HO-95) Additional Resources American Nursery and Landscape Association. Resource References Catalog. 250 I St. NW, Suite 500, Washington, DC Craul, P.J. Urban Soil in Landscape Design. New York: John 20005-3922. Wiley & Sons, 1992. American Nurseryman Publishing Co. (distributes many books Dirr, Michael A., Dirr’s Hardy Trees and Shrubs: An Illustrated of horticultural interest). Suite 2100, 77 W. Washington St., Encyclopedia. Portland, OR: Timber Press, 1997. Chicago, IL 60602-2904. Dirr, Michael A., Dirr’s Trees and Shrubs for Warm Climates: International Society of Arboriculture. www.treesaregood.com. An Illustrated Encyclopedia. Portland, OR: Timber Press, 2002. Dirr, Michael A., Hydrangeas for American Gardens. Timber Press: Portland, OR, 2004. Revised 01-2024