Mint Plant Morphology

Study Notes

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.

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.

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.

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.

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.