Lemon balm

Family

Lamiaceae

Habit

perennial

Height

0.6 m

Spread

0.1 m

Growth

medium

Lifespan

8 years

First yield

after 1 year

Hardiness

zone 5–9

Shade tolerance

partial shade

Soil

Loam

Soil moisture

semi-dry – very moist

pH

5.5 – 7.5

Edible: Lemon balm leaves are at their best fresh — drying drives off much of the citral, and the lemon note gives way to something hay-like. They are most aromatic just before flowering; after that the essential oil declines and the leaves toughen. Chopped fresh they go into salads, sauces, quark and compote as well as fruit desserts and fruit salads, where they round off the acidity without masking it. Whole shoots go into cold drinks, punches and lemonades. As a tea, balm is among the most widespread household blends there is. Leaf extracts go into herbal liqueurs, and a balm wine can be made as well. The vitamin C content of the fresh plant is a remarkable 253 mg per 100 g.

Medicinal: The leaves are the part used as a drug (Melissae folium). Traditional use is directed at supporting stomach function and at nervous strain: tea infusions as well as liquid and dry extracts are regarded as calming and antispasmodic and are used for difficulty falling asleep and for digestive complaints, often in blends with other calming drugs. Baths are used for skin inflammation and for relaxation. Because of their content of phenolic acid derivatives, above all rosmarinic acid, balm leaves have an antimicrobial and antiviral action; this is used in ointments for treating herpes simplex. Also recorded in folk medicine, without evidence of efficacy, is its use for colds and for circulatory weakness. As so-called cloister balm the plant is one of more than ten terpene-bearing source drugs of Klosterfrau Melissengeist.

Other uses: Balm oil is distilled from the herb and smells intensely of lemon thanks to its high citral content. Because the oil content of the plant is very low at 0.05 to 0.3 percent — even selected cultivars reach only 0.8 percent — enormous quantities of herb yield very little oil, and the price stands at around 6000 euros per kilogram. Product sold as "balm oil" is therefore usually citronella or lemongrass oil. As so-called cloister balm the plant is also one of more than ten terpene-bearing source drugs of Klosterfrau Melissengeist. In the garden its most practical secondary use is scent: planted along path edges and seating areas it releases a lemon fragrance at every touch, and the dried herb fills scented sachets.

Site: Lemon balm is undemanding but wants warmth and free-draining soil; on heavy, wet ground the crowns rot in winter. Sun and partial shade both suit it, though in partial shade the leaves stay softer and milder. The decisive planning point is the creeping rhizome: the plant widens slowly and seeds itself freely as well — in a tidy perennial border it becomes a nuisance, in a herb spiral, beneath fruit trees or on a bank that is exactly what is wanted. A root barrier or a container keeps it in check. Shallow-rooted and only 40–80 cm tall, it makes good underplanting for deeper-rooting shrubs and trees. By a path or a seat it gives off lemon scent when brushed and is at the same time strong bee forage. Care: Little work is needed, and slugs leave it alone. Harvest three to four times a year, each time just before flowering and a hand's width above the ground; it regrows quickly. Letting it flower gives you the bee forage but costs aroma and brings copious self-seeding — cutting back straight after flowering prevents both. In late autumn the dead stems are left standing and removed only in spring, as they protect the crown. It is hardy to about −34 °C. Feed moderately with compost; too much nitrogen makes the leaves large and poor in essential oil. After three or four years the clumps go bare in the middle — then divide and replant. Diseases and pests play almost no part.

Lemon balm can be propagated three ways. Dividing the crown in spring or early autumn is the quickest method and at the same time the way to rejuvenate bare clumps: the lifted rootball is broken into fist-sized pieces each carrying a few shoots and replanted at once. Cuttings from non-flowering shoots root without trouble in summer, even in a glass of water. For seed: it needs light and warmth to germinate, so it is pressed down only and not covered with soil, and wants temperatures around 20 °C. Raise from March, plant out in May or September at about four plants per square metre; direct sowing outdoors is worthwhile only from May. Oil-rich selections are propagated vegetatively alone, because seedlings vary widely in aroma.

Lemon balm is a decidedly good insect plant with a long flowering season. NaturaDB counts 37 wild bee species, two of them specialists, and three caterpillar species; nectar and pollen value each stand at 2 out of 4 — the strength lies less in the yield of the individual flower than in the quantity and duration of the supply. It is pollinated mainly by honeybees and bumblebees, and also by hoverflies. The inconspicuous white labiate flowers open in succession over weeks and so fill the gap between the flowering peaks of early and late summer. As an archaeophyte it is firmly embedded in the native insect fauna. To get that value, though, you have to let it flower: the usual harvest just before flowering removes precisely that supply. Leaving part of the stand standing resolves the conflict.

Special features: aroma only when fresh, drying drives off the citral; most aromatic before flowering, can be cut 3-4 times a year; creeping rhizome plus strong self-seeding -> it travels, use a root barrier or a container; needs light and warmth to germinate (around 20°C), do not cover the seed; clumps go bare in the middle after 3-4 years -> divide; slugs leave it alone; conflict between harvest and bee forage -> let part of the stand flower; archaeophyte, present in Central Europe before the 15th century

Eastern Mediterranean and Western Asia: from Anatolia across the Caucasus, Iraq and Iran to Pakistan, Turkmenistan, Uzbekistan and Kyrgyzstan. Lemon balm reached Central Europe early as a medicinal and culinary plant — it counts here as an archaeophyte, present before the 15th century — and spread onward through monastery and cottage gardens. Today it is cultivated worldwide in temperate and warm regions and escapes regularly in the process; in Central Europe such populations are found above all on forest clearings and along forest roads. In the Swiss canton of Valais it reaches 990 m above sea level.

In its native range lemon balm grows in the open understorey of deciduous woodland, above all in hop-hornbeam forests of the submediterranean mountain belt. There it occupies warm, nutrient-rich and rather dry sites on humus-rich sandy loam or loamy sand of neutral to basic reaction. It does not need full sun — by Landolt's indicator values it is a plant of partial shade in warm positions. In Central Europe escaped plants hold on in comparable places: woodland margins, clearing vegetation and banks along forest tracks, where warmth and open ground come together. Its creeping rhizome carries it through the winter underground, and it shoots again in spring.