Mint Plant Morphology

Plant Description

• There are over 25 types of mint, many of which cross-pollinate to produce variable hybrids.
• Peppermint stems are usually dark green with purplish stems, but can also be "white" with green stems and leaves.
• Leaves are narrow and tapering, sharply serrated, and can be almost smooth or thinly haired.
• Leaves are 4-9 cm (1.6-3.5 in) long and 1.5-4 cm (0.59-1.57 in) broad, with dark green color, reddish veins, and an acute apex.
• Flowers are purple, 6-8 mm (0.24-0.31 in) long, with a four-lobed corolla about 5 mm (0.20 in) diameter, and produced in whorls around the stem.
• Plant is a herbaceous rhizomatous perennial, growing to 30-90 cm (12-35 in) tall, with smooth stems, square in cross section.
• Rhizomes are wide-spreading, fleshy, and have bare fibrous roots.

Distribution and History of Cultivation

• Mint is believed to have originated in the Mediterranean basin and spread to the rest of the world through natural and artificial means.
• Peppermint is found growing wild throughout Europe, North America, and Australia along stream banks and in moist wastelands.
• It is also cultivated under various varieties, strains, or chemotypes.

Propagation

• Propagated by division in spring or autumn, or by tip cuttings in spring or summer.
• Easy to root if the sprigs are kept standing in water for a few days.
• As a hybrid, it is sterile and produces no seeds.

Ecology

• Prefers fertile, moist soil in full sun or partial shade.
• Requires well-tilled soil, 20-25 cm deep, with a pH of 6-7.5.
• Can be invasive if growing conditions are ideal.
• Temperature: grown in cool to temperate regions, needs long day lengths with warm to hot conditions and cool nights for optimal oil production.
• Requires ample sunshine during most part of the growing period, and shade is undesirable as it induces higher ester and menthone content in the oil.
• Less desirable compounds, particularly menthofuran, form when the conditions are too warm, especially at night.

Day Length

• Long day length is a determining factor contributing towards higher oil yield and its quality.
• 15 h day length is essential, and for economic production of the oil, the day length must approach 16 h.
• Differences in plant morphology exist between plants grown under long-day and short-day conditions.
• Long-day plants often have: larger leaves, a more erect habit, and fewer stolons than short-day plants.
• Mint grown in long-day conditions produced oil with more menthone and menthol and less menthofuran than short-day conditions.