Lemon balm

Identification and origin

Melissa officinalis belongs to the mint family, Lamiaceae, along with thyme and sage. Its native range runs from the Mediterranean to Central Asia: the Iberian Peninsula, southern France, Italy and the large Mediterranean islands, the Balkans, Greece and Crete, North Africa from Morocco to Tunisia, Turkey, Cyprus, the Middle East, Iraq, Iran, the Caucasus and the Central Asian republics. It has naturalized across much of northern Europe, North and South America, New Zealand and Tasmania.

It is a bushy, rhizomatous herbaceous perennial, 18 in – 3 ft tall and about as wide. The stems are square, branched, sometimes finely hairy, and become somewhat woody with age. The opposite leaves, light to medium green, oval or heart-shaped, crinkled, coarse and hairy with scalloped edges, are 2–4 in long. When crushed they smell strongly of lemon.

In summer, tiny two-lipped flowers, creamy white and sometimes tinged yellow or pink, appear in small clusters in the axils of the upper leaves. They are not showy but are rich in nectar and draw bees and butterflies: the name Melissa comes from the Greek word for honeybee. Each flower produces four small nutlets. Don’t confuse it with bee balm (Monarda), to which it is not related.

The young leaves, more flavorful than older ones, season teas, salads, soups, fish, egg dishes, jellies and vinegars.

Common cultivars: ‘All Gold’ (or ‘Gold Leaf’), entirely golden and best in part shade; ‘Aurea’, splashed with yellow; ‘Variegata’, with golden yellow margins that fade in summer; ‘Compacta’, compact and sterile; ‘Lime’, with a lime scent; ‘Mandarina’, with a mandarin orange scent; ‘Lemona’, selected for essential oil.

Light

Lemon balm grows in full sun or part shade. Some shade gives larger, more tender leaves. Golden cultivars hold their color without scorching in part shade.

Watering

It grows best when it never runs short of water, but it hates excess: keep the soil moist, never soggy. Before watering, push a finger into the soil: if it is dry a little way down, water; if it is still damp, wait.

Once well established in the ground, it tolerates drought. An organic mulch (grass clippings, leaves, bark, compost) reduces evaporation and weeds. Water after a hard cutback to help the plant recover. Overwatering encourages powdery mildew and root rot.

Potting mix

Choose fertile, humus-rich, moist, well-drained soil. Once established, lemon balm also copes with poor soil. In a container, use a rich, free-draining potting mix.

Go easy on fertilizer: an all-purpose fertilizer in spring to start growth, then a light feeding after a large harvest. Too much fertilizer produces lots of foliage but poor flavor.

Temperature

Very hardy, lemon balm is grown in USDA zones 3a to 9b. Mulch young plantings heavily as winter approaches to improve their survival. Where winters are too harsh, grow it as an annual.

Repotting

Plant in early spring, spacing plants 18 in – 2 ft apart. It spreads by rhizomes and above all by abundant self-sown seedlings: growing it in a container on a patio or deck is the best way to keep it in check. In the ground, dig around the edge of the clump now and then to limit its spread.

Clumps decline after three or four seasons: divide or replace them at that point.

Pruning

Pruning is part of growing it. Cut flower stalks before they set seed, to prevent invasive seedlings and keep the foliage fresh. After flowering, cut back hard, to about half its height, for a fresh flush of leaves. In midsummer, thin dense clumps by removing some stems to let air through.

Harvests double as pruning. Harvest preferably before flowering, without bruising the leaves. In the first year, cut just the tips of the stems; after that, two or three cuttings a season are possible, taking about a third of the foliage each time. Dry the stems in bundles, hung upside down in a dark, airy place, then store the leaves in a closed container. They can also be frozen; drying costs them much of their scent.

Propagation

Division is the easiest method: in spring, or between late summer and early fall, dig up a piece of crown with three or four buds and replant it. A division made at that time has time to root before frost.

Layering is very reliable: choose a flexible, low stem 6–12 in long, make a small cut on its underside, pin it to the ground and cover it with 2–3 in of soil. Roots form near the cut in one to two months; then sever the young plant.

Sow seed indoors four to six weeks before the last frost. The seeds are very fine: cover them with a thin layer of soil kept moist; germination is slow. Transplant when seedlings are 2–3 in tall. You can also sow outdoors in late spring or in fall. Stem cuttings also work.

Common problems

• White powdery coating on leaves: powdery mildew, encouraged by overwatering and a clump that is too dense.
• Spots and blight on the foliage, gray mold: leaf spot, leaf blight or gray mold.
• Plant wilting in moist soil: root rot from overwatering.
• Pests: aphids and mites can slow growth.
• Seedlings all over the garden: flowers left to set seed.
• Sparse, weak clump: a plant more than three or four years old, or a lack of pruning.

The same symptom can have several causes: look at watering, clump density, exposure and plant age together. Deer and rabbits rarely eat it.

Toxicity

No toxicity is reported: lemon balm is listed as nontoxic to dogs, cats and horses, and its leaves are commonly eaten in cooking and teas.