How to Grow Nettles in Australia

Nettle (Urtica dioica, family Urticaceae), the stinging or common nettle, is a fast-growing perennial grown for its young leafy tops. It also feeds butterfly caterpillars and gives rich material for compost and liquid feed. The store sells nettle seeds of this European and Asian species, which grows 60 to 150 cm and spreads into clumps by creeping roots. The step to get right is leaving the seed uncovered, because darkness stops it germinating.

Three mistakes that matter

1. Burying the seed. Nettle seed will not germinate in darkness, so a layer of mix on top can leave a tray bare. Press it onto the surface, or give it a dusting of 2 mm at most, as Germinating the seed describes.
2. Planting it loose in a bed. Creeping underground stems carry one plant well beyond where it was sown, and a patch soon crowds out its neighbours. Grow it in a large pot or behind a buried barrier, as Container growing explains.
3. Hot, dry, hungry soil. Nettle is not drought tolerant: it goes limp as the soil dries and stays stunted in poor ground. Give it rich, moist soil, a mulch, and afternoon shade in hot districts.

When to plant

Seed germinates well at about 18 to 22°C in light, and a cooler night than day helps it along. Below about 15°C it still comes up, but over weeks rather than days. Sow from spring to early summer, and again in early autumn where winters are mild. One sowing is usually enough, because the plants come back from their roots each year.

At the cold edge of a window, start seed indoors on a bright windowsill or a heat mat. In frosty districts, a pot sown in autumn and left outdoors over winter often comes up by itself in spring.

Site, soil and setup

Nettle follows people and livestock. It springs up among cow pats in paddocks and on the sites of old settlements, where the soil is rich, especially in phosphorus. Copy that in the garden with moist, fertile ground and some shelter from hot afternoon sun.

Container growing

A pot is the simplest way to keep nettle in its place. Give one plant a pot of at least 30 L and 40 cm across, filled with premium potting mix and a few handfuls of compost. Stand it on paving rather than soil, so roots cannot escape through the drainage holes.

• Watering: keep the mix evenly moist, and check pots daily in hot weather, when they dry fast.
• Feeding: fish and seaweed blend at half strength, about 12 mL per 9 L, fortnightly in spring and summer.
• Position: morning sun and afternoon shade, away from paths where people and pets brush past.
• Renewal: lift, divide and repot once roots fill the pot, usually every year or two.

Dividing a crowded clump is covered in dividing perennials.

Germinating the seed

Nettle seed has no deep dormancy; what it needs is light. In British laboratory tests, soaked seed germinated well in light and even in deep shade, but not at all in darkness. Alternating warm days and cooler nights also spur it on, which is why seed on bare, freshly dug soil comes up so readily.

This is not hard seed. Fresh seed gave 60 per cent germination at 20°C in one study, half of it within a week, and months of chilling made little difference. In Kew's seed bank tests at cooler or alternating temperatures, 52 to 86 per cent came up over 7 to 11 weeks. The seed is dust-fine, roughly 5,000 to 10,000 to the gram, so sow a pinch of three or four for each plant you want.

For handling seed this small, see how to sow tiny seeds without losing them.

When nothing comes up

• Buried or kept dark. Seed under a layer of mix, or kept in the dark, stays put. Sow again on the surface, in the light.
• Dried out. Surface seed dries fast. Keep a clear lid on the tray and mist it until the first leaves show.
• Too cold. Cool mix slows it: Kew's tests at 10 and 15°C ran for 7 to 11 weeks. Move the tray somewhere warmer, or onto a heat mat.
• Old or badly stored seed. Seed usually keeps for about 3 years when stored cool and dry in a sealed container.
• Given up too soon. Keep a slow tray moist and in the light for eight weeks before resowing. Seed that sits out a winter can still come up in spring.

Sowing Seeds

Start nettle in cells for the most control, or scatter it where it is to grow, inside its pot or barrier. Both begin with seed pressed onto the surface, as Germinating the seed explains.

Starting in trays

• Fill a punnet or cell tray with fresh seed raising mix, firm it lightly and water it well.
• Press a pinch of three or four seeds onto each cell, and do not cover them.
• Keep the tray under a clear lid in bright, indirect light, at the warmth given in When to plant.
• Lift the lid once seedlings show, and keep the mix moist.
• Thin each cell to the strongest seedling once the first true leaves appear.
• Wear gloves from the start, for sowing and transplanting as well as picking.

Sowing direct

Rake a fine, moist seedbed inside the barrier, mix the seed with a little dry sand and scatter it thinly. Press it in with the back of the rake and mist it daily until seedlings show. Thin them to the spacing in Site, soil and setup.

Planting out

• Plant out when seedlings have two or three pairs of true leaves, usually 4 to 6 weeks after sowing.
• Harden them off first (stand the pots outdoors a little longer each day for a week, so they adjust to sun and wind).
• Plant at the same depth as in the pot and water in with seaweed solution at half strength, 15 mL per 9 L.
• Water deeply after planting, then whenever the top few centimetres of soil are dry.

More on the move from pot to garden is in hardening off seedlings before planting out.

Care by growth stage

Moisture and fertile soil decide how well nettle grows. Plants that never dry out, and are cut back as they start to flower, keep producing soft, leafy shoots.

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

Cutting Back

Cutting plants back as they come into flower brings a flush of soft new shoots, richer in water and nitrogen than the old growth. It also stops female plants seeding across the garden. Wear gloves and long sleeves for every cut.

• Cut all stems close to the ground with shears once the green flower tassels appear.
• Slice a spade around the pot or barrier each spring to cut any runners that have crept over.
• In frosty districts, clear the dead stems in winter; shoots return from the roots in spring.
• Put cut stems in the compost before seed forms, or into a bucket for liquid feed, as Tips explains.

Cutting every shoot as it reaches 15 to 30 cm is the recognised way to kill a nettle patch. Let plants regrow well past that between cuts.

Companion planting

Nettle suits a damp, rich, part-shaded corner, and its neighbours there need to hold their own.

Grows well with

• Comfrey, which wants the same rich, moist soil and is also cut for compost and liquid feed.
• Mint, another runner, which suits a sunk pot or barrier in the same damp corner.

Keep apart

• Vegetable beds and low herbs, since its dense canopy and spreading roots crowd them out.
• Paths, play areas and gates, where people and pets brush past the stinging hairs.

Harvesting Leaves and Tops

Pick the soft tops while plants are 15 to 30 cm tall and before they flower, usually from about 11 to 13 weeks after sowing. After that, pick from each flush of regrowth that follows cutting back.

• Wear gloves and long sleeves, and pick on a dry day.
• Take the top two or three pairs of leaves from each stem.
• Take no more than a third of a plant at one picking.
• Skip old and flowering growth: by autumn the leaves turn gritty with mineral crystals.
• Never pick from roadsides, drains or soil that may be contaminated.

Use fresh tops the day they are picked. To dry them, spread the leaves one layer deep on a screen in an airy, shaded place until crisp. Store them in a sealed, labelled jar away from light. Cooking or drying disarms the stinging hairs, and the cooked tops are used like spinach, in soups, or blanched for salads. The stinging hairs on leaves and stems inject histamine and other irritants, so never eat the leaves raw; see Safety.

Traditional use and history

Nettle is native from Europe to Siberia and western China, and to north-western Africa. Its genus name Urtica comes from the Latin uro, to burn. The name dioica means two houses, because each plant usually bears only male or only female flowers. Grieve's A Modern Herbal traces the English name to the Anglo-Saxon netel. It may come from a word for a needle, or from an old verb meaning to spin and sew.

Grieve records the old rhyme "Nettle in, dock out", spoken over a sting. In Hans Christian Andersen's fairy tale of the princess and the eleven swans, she weaves their coats from nettles. In Britain it has become the most abundant broad-leaved plant in the national Countryside Survey, and needs no protection.

Safety

Happy Valley Seeds sells nettle as seed for growing. Nothing here is advice to eat or take any part of the plant. Anyone considering using a plant should first seek advice from a qualified health practitioner.

For a nettle sting, wash the skin with soap and water, do not scratch or rub it, and apply a damp cloth or ice pack. See a doctor if the pain has not eased after 2 hours. For breathing trouble, a swollen tongue or throat, or collapse, call triple zero (000). For poisoning advice, call the Poisons Information Centre on 13 11 26.

Common problems

No seedlings. Usually seed buried, kept dark or allowed to dry out; see Germinating the seed and its list, When nothing comes up.

Limp, scorched plants in summer. Nettle wilts once the soil dries, and hot sun makes it worse. Water deeply, mulch, and give it afternoon shade.

Pale, stunted growth. Poor soil, often short of phosphorus, holds nettle back. Dig in manure or compost and feed as Care by growth stage sets out.

Tough, gritty leaves. Old and flowering growth coarsens; cut plants back, as Cutting Back explains, and pick the regrowth.

Nettles popping up across the garden. Runners and self-sown seed carry it well beyond its bed; see Three mistakes that matter and Cutting Back.

Plants dying in wet ground. Roots cannot survive long spells of waterlogging. Move plants to better-drained soil or a pot.

Pests and diseases

Snails and damping off trouble the seedlings, and older plants feed a native butterfly worth keeping.

Yellow admiral (Vanessa itea). Grey-green to black caterpillars with a yellow side band live inside folded leaves and eat the soft growth. This native butterfly has taken to introduced nettles, so leave them be: the spines are harmless to people.

Common garden snail (Cornu aspersum) and slugs. Snails and slugs find nettle leaves palatable and graze seedlings at night in damp weather. Hand-pick them after dark, or scatter an iron-based snail bait thinly as the label directs. Read more

Damping off (Pythium species and Rhizoctonia solani). Seedlings rot at soil level and collapse, most often in wet mix. Use fresh seed raising mix and clean trays, and avoid overwatering. Read more

Prevention first

• Keep seed trays clear of rain and hose splash, which spread damping off.
• Water the soil, not the tops, and mulch to keep the roots evenly moist.
• Clear boards, loose pots and leaf litter from around seedlings, where snails shelter.
• Check plants weekly, and look inside folded leaves before spraying anything.

Tips

1. Drown cut stems in a bucket of water for a few days to make liquid feed. Dilute it 1 part to 10 parts water before use.
2. Add cut stems to the compost before seed forms, where they help the heap break down faster.
3. Keep one pair of heavy gloves for nettle work only, since the hairs cling to fabric.
4. Leave a small patch uncut in spring for yellow admiral caterpillars, and cut the rest for picking.