How to Grow Lemon Balm in Australia

Lemon balm (Melissa officinalis) is a hardy, clump-forming perennial of the mint family, Lamiaceae, grown for its lemon-scented leaves, used fresh in the kitchen. It grows happily in part shade, so it suits the shady side fence of a Melbourne yard or a Brisbane courtyard. The usual mistake is letting it flower and drop seed, which has let it escape into creek banks and drains in parts of south-eastern Australia.

Three mistakes that matter

1. Burying the seed. The seed is small and some light helps it germinate, so a normal covering of mix leaves a bare punnet. Press it onto the surface, or cover it with no more than 2 to 3 mm of fine mix.
2. Letting it set seed. A clump left to flower drops seed everywhere, then turns straggly with tatty leaves. Cut the flowering stems as the flowers fade and before seed forms, as Cutting Back describes.
3. Leaving the shallow roots to bake. In hot, dry weather the roots dry out fast and the plant wilts and stops growing, yet cold, soggy soil rots them in winter. Give afternoon shade in hot zones, mulch well and keep the soil moist, never wet.

When to plant

Seed germinates with the soil or mix at about 10 to 25°C, and comes up in 7 to 14 days at 19 to 22°C. Most zones sow from late winter into spring, while the tropics and the inland sow as the weather cools. One or two plants supply most kitchens and return each year, so one sowing is enough.

At the cold edge of a window, raise punnets indoors or on a seedling heat mat. At the hot edge, keep trays in bright shade and never let the mix dry.

Site, soil and setup

Lemon balm grows in most soils, provided water drains away and the shallow roots never dry out completely.

A clump stays put for years; when one is replaced, plant the new pieces in fresh soil where no roots have rotted.

Container growing

A pot is the surest way to stop the clump spreading. Give one plant a pot at least 25 cm wide and deep, filled with premium potting mix. A standard 30 cm pot holds about 13.5 L and gives more room. Both packets, lemon balm seeds and organic lemon balm seeds, grow the standard form, 30 to 90 cm tall.

• Water: keep the mix evenly moist, and never leave the pot standing in water.
• Feed: fish and seaweed blend at half strength, about 12.5 mL per 9 L, fortnightly from spring to early autumn.
• Position: morning sun and afternoon shade, moved to a sheltered spot out of heavy winter rain.

Sowing Seeds

Start lemon balm in a punnet of seed-raising mix, then plant it out once it is big enough to handle.

Starting under cover

• Scatter the seed thinly over moist seed-raising mix and press it in, or barely cover it with fine mix.
• Keep the mix warm (see When to plant), under a clear cover in a bright spot, and mist it so it never dries.
• Seedlings can take up to three weeks; lift the cover once they appear.
• At four true leaves, move each seedling into its own small pot, holding it by a leaf, never the stem.
• Seed-raising mix can carry Legionella bacteria, so dampen it first, wear gloves and a P2 mask, and wash your hands afterwards.

Seed can also go straight into a fine, weed-free bed during your zone's sowing months, sown thinly and barely covered. Keep it damp until seedlings show, then thin them to the spacing below.

Planting out

• Harden off the young plants (move them outdoors a little longer each day so they adjust to sun and wind) over about a week.
• Plant out at 5 to 10 cm tall, at the depth they grew in the pot.
• Space plants 40 to 50 cm apart, because clumps widen quickly.
• Water in with seaweed solution at half strength, 15 mL per 9 L, then mulch with straw.

Care by growth stage

Steady moisture and restraint with feeding decide how well it grows. Over-feeding reduces the essential oils that give lemon balm its flavour and aroma, so feed at half strength at most.

If growth stalls in very poor, sandy soil, a light scatter of all-purpose controlled release granular (NPK around 14-5-10) in spring can help.

Cutting Back

Hard cutting keeps lemon balm leafy, stops it seeding through the garden and fixes the straggly look it takes on after flowering.

• Pick often, since regular harvests keep the plant bushy and compact.
• Cut off flowering stems before they set seed.
• In midsummer, thin out stems to let air through, or cut the plant back to half its height.
• After flowering, cut the whole plant down to just above the base for a fresh flush of leaves.
• Where tops die down in winter, cut the dead stems at ground level before spring growth.
• Every few years, lift and divide the clump in spring or autumn, and replant healthy pieces.

Companion planting

Lemon balm flowers are small but rich in nectar, and bees work them hard, which helps any crop that needs pollinating.

Grows well with

• Onions and spring onions, which Australian planting charts list as good neighbours.
• Zucchini and pumpkins, whose flowers need bees to set fruit.

Keep apart

• Mint, which spreads by underground stems, and the two tangle into one clump that is hard to separate.
• Thyme and oregano, low herbs that a leafy clump up to 90 cm tall shades out.

Harvesting Leaves

Start picking about 8 to 10 weeks after sowing, once the plant is growing strongly; the scent is strongest just before it flowers.

• Pick the youngest leaves and shoot tips, which carry the best flavour.
• Take stems from the outside of the clump.
• Take about a third of the foliage at a time, roughly monthly.
• Handle the stems gently, since bruised leaves lose quality.
• Cut whole stalks for drying before the plant starts to flower.

Use the leaves as fresh as possible, since they lose much of their scent when dried. To dry them anyway, hang small bundles in a warm, dark, airy spot, then strip the leaves into a sealed container. Leaves can also be frozen.

Chop the leaves into salads and fruit salads, add them to fish, chicken and desserts, or add them to cold drinks and tea.

Common problems

No seedlings. Seed covered too deeply or left to dry out rarely comes up, so see Three mistakes that matter and sow again. Read more

Tall, pale seedlings. Seedlings kept in too little light stretch towards it, so move the punnet to bright light at once. Read more

Collapse in wet weather. Roots left in cold, soggy soil rot, as Three mistakes that matter warns, so replant a healthy division in freer-draining ground.

Pests and diseases

Lemon balm is generally healthy; most trouble comes from sap-sucking insects in warm weather and snails on young plants.

Aphids, such as green peach aphid (Myzus persicae). Colonies on soft tips stunt young plants, distort leaves and leave sticky honeydew. Squash small colonies by hand, or spray leaf undersides with an insecticidal soap, following its label and withholding period. Read more

Greenhouse whitefly (Trialeurodes vaporariorum) and silverleaf whitefly (Bemisia tabaci). Tiny white-winged insects gather under the leaves, leaving honeydew and sooty mould. Silverleaf whitefly is found mainly in Queensland, the Northern Territory, New South Wales and Western Australia. Hang yellow sticky traps nearby and aim any spray at the undersides of the leaves. Read more

Two-spotted mite (Tetranychus urticae). These mites, under 0.5 mm, suck the leaves from below and leave pale stippling, and they build up fast in hot, dry weather. Hose the undersides of the leaves regularly and avoid sprays that kill predatory mites. Read more

Slugs and snails, mainly the garden snail (Cornu aspersum). They chew newly planted seedlings to the ground and leave silver trails, mostly at night after rain. Hunt with a torch about two hours after sunset, and ring pots with copper tape. Read more

Powdery mildew (Golovinomyces species). A white, powdery coating spreads over the leaves, worst in humid weather with cool nights. Cut back affected stems, pick often to open the clump, and spray 1 part full-cream milk to 10 parts water. Read more

Damping off (Pythium and Rhizoctonia species). Seedlings collapse at soil level, most often in wet mix sown thickly. Sow thinly into fresh mix, avoid overwatering and keep trays well drained. Read more

Prevention first

• Keep the spacing Planting out gives, so air moves through each clump.
• Water the soil rather than the leaves, and early in the day.
• Check the undersides of leaves weekly in warm weather.
• Grow flowering plants nearby, since ladybirds, lacewings and hoverflies eat aphids.

Tips

1. Lift self-sown seedlings in spring while they are small, and pot them up to share.
2. Stand cut stems in a jar of water; they root readily and can then be potted up.
3. Plant a clump beside a path, where brushing past it releases the lemon scent.