How to Grow Selfheal in Australia

Selfheal (Prunella vulgaris, family Lamiaceae) is a low, creeping perennial of the mint family, grown for its dense spikes of violet, two-lipped flowers. It makes a soft ground cover, a flowering lawn plant and a steady source of nectar for bees, 10 to 30 cm tall in flower. The store sells selfheal seeds of the common species. The seed is among the easiest of the traditional herbs to raise. Where gardeners go wrong is afterwards: a patch left to seed spreads well beyond its bed.

Three mistakes that matter

1. Burying the seed. The seed is tiny, about a thousand to the gram, so it belongs within a few millimetres of the surface. Sow it on the surface, barely covered, as Germinating the seed describes.
2. Letting it seed into lawns and bushland. Selfheal has escaped gardens into stream banks, pastures and roadsides, and its seed can lie in the soil for at least five years. Cut off the flower spikes as they fade; Safety gives its status by state.
3. Treating it as a dry-garden plant. In a long dry spell it drops its lower leaves and turns yellow-green. Give it moist soil and, in hot districts, afternoon shade, and water new plants through their first year.

When to plant

The seed germinates freely anywhere from 15 to 25°C, so sow while the soil or trays sit in that range. That puts the main windows in spring and autumn in the south, and in the cooler, drier months in the north. One sowing is usually enough, because an established patch keeps itself going by creeping stems and self-sown seedlings.

In fields grown for seed, few plants flower in year one, more from autumn sowings, so a patch usually flowers best in its second summer. At the hot edge of a window, sow in a shaded tray and keep it evenly moist.

Site, soil and setup

In the wild it follows damp ground: stream banks, moist meadows, woodland edges and roadside drains. Match that in the garden with steady moisture and some shade from the hottest sun. Keep it well back from creeks and bushland.

Container growing

A pot holds its creeping stems in check, which suits a small garden. Seed still travels on water, birds and animals, so deadhead potted plants too. Choose a wide, shallow pot at least 25 cm across and about 8 L, filled with a premium potting mix.

• Watering: water when the top 2 cm of mix feels dry; pots dry faster than beds, so check daily in hot weather.
• Feeding: fish and seaweed blend at half strength, about 12 mL per 9 L, fortnightly in spring and summer, only if leaves look pale.
• Position: morning sun and afternoon shade, or bright dappled light under a tree.

Germinating the seed

Selfheal seed has little or no dormancy. A United States Department of Agriculture fact sheet describes high germination at most temperatures with no pretreatment. The Millennium Seed Bank at the Royal Botanic Gardens, Kew, recorded 94 to 100 per cent in most of its tests across that range.

Those tests ran on a moist gel surface in daily light, and counted seedlings over two to eight weeks. Garden guides give 10 to 21 days for most seed, with stragglers for up to eight weeks. Sow two or three seeds for each plant you want, then thin.

Seed banks have also tested gibberellic acid, but untreated seed at steady warmth reached the same high rates, so no chemical is needed. For seed treatments in general, see soaking, scarification and cold stratification.

When nothing comes up

• Buried too deep. Seed under more than a few millimetres of mix may never show. Sow again on the surface, barely covered.
• Dried out. Tiny surface seed dries in an afternoon. Cover the tray with clear plastic or glass, lift the cover once seedlings show, and water from below.
• Too hot. Trays in full summer sun can climb well above 25°C. Move them into bright shade, or wait for autumn.
• Old or warm-stored seed. The seed stores well cool and dry; stored seed still gave 85 per cent after a year at 5°C. Keep packets sealed in the fridge.
• Given up too soon. Keep the tray moist and in the light for eight weeks before resowing. Outdoor autumn sowings may wait for spring.

Sowing Seeds

Start selfheal in trays for plants that fill a pot or bed quickly, or scatter it where it is to grow. Both begin with seed sown on 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.
• Sow each cell at the rate and depth given in Germinating the seed.
• Keep the tray at the warmth given in When to plant, in bright, indirect light, and never let it dry.
• Thin to the strongest seedling per cell once the first true leaves open.
• Move seedlings into 9 cm pots once they are large enough to handle.

Mixing the seed with dry sand makes it far easier to spread evenly. See how to sow tiny seeds for the sand method.

Sowing direct

Rake the soil fine and level, water it, then scatter the seed thinly and press it in with the back of a rake. Keep the surface damp until seedlings show, then thin them in stages to the spacing in Site, soil and setup.

Planting out

• Plant out in spring or autumn, once seedlings have several pairs of leaves.
• Harden them off first (stand the pots outdoors a little longer each day for about a week, so they adjust to sun and wind).
• Set each plant at the depth it grew in the pot, at the spacing in Site, soil and setup.
• Water in with seaweed solution at half strength, 15 mL per 9 L.
• Keep the soil moist until new growth shows, and water through the first dry season.

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

Care by growth stage

Steady moisture decides how well selfheal grows; feeding matters little. Like most herbs it needs restraint, so feed at half strength at most.

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

Trimming and Deadheading

Trimming keeps selfheal dense and, more importantly, keeps its seed at home. The flowers open in tiers up the spike, so a spike can look ragged while still flowering.

• Cut spent flower spikes off as the last flowers fade, before the brown seed heads ripen.
• Shear the whole patch back after the main flowering to renew the foliage.
• Mow a lawn planting as you would the grass; it keeps flowering even when mown fairly short.
• Cut back taller plants around it at the end of the season, so they do not smother it.
• Lift runners that root into paths or beds, and pot them up or discard them.
• Divide crowded clumps in spring or autumn to renew a tired patch.

Division is the quickest way to more plants: see dividing perennials for the method.

Companion planting

Choose low neighbours that like the same moist soil, because taller, vigorous plants shade selfheal out.

Grows well with

• Violas, low and happy in the same moist, part-shaded ground.
• Forget me nots, which share the damp, dappled edges of a garden.
• Alyssum, a low edging that flowers alongside it and leaves it the light.

Keep apart

• Tall, dense perennials, which shade it out within a season.
• Vegetable beds and fine lawns, where its runners and seedlings become a weeding job.

Harvesting Leaves and Flowers

Cut flowering stems on a dry morning when most spikes are in full flower; in New South Wales it flowers from November to April. Leafy shoots can be picked at any time once a plant has spread well.

• Pick only from unsprayed plants in clean garden soil, as Safety explains.
• Cut stems about 5 cm above the ground with clean scissors or secateurs.
• Take no more than a third of a patch at one picking.
• Shake off insects and discard yellowed or damaged leaves.
• Tie small, loose bunches and hang them in an airy, shaded place indoors.
• Dry until the leaves crumble and the stems snap cleanly.

Store the dried stems in a closed, labelled jar in a cool, dry, dark place.

Traditional use and history

Selfheal grows wild across Europe, much of Asia, north-west Africa and North America. It has been recorded in herbals for close to two thousand years. Its many English names include prunella, sicklewort, carpenters weed, blue curls, heart of the earth and thimble-flower.

Grieve's A Modern Herbal notes that it found its way from Europe to North America, where it tended to crowd out native flowers. The same has happened here: selfheal is now naturalised in every Australian state and the ACT.

The Chinese name means summer-withering herb. It was given, a review of the old texts explains, because the plant flowers in spring and dies back after summer. The spikes were gathered in summer, once they had turned brownish red.

In the seventeenth century, William Cole traced Brunella to a German name for a mouth and throat inflammation among soldiers in camp. He took the throat-like shape of the flowers as a sign, a belief known as the doctrine of signatures. In the eighteenth century, Linnaeus used the spelling Prunella.

Safety

Happy Valley Seeds sells selfheal as seed for growing, as an ornamental and bee plant. 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.

The sources name no toxic look-alike, but bugle (Ajuga species) has similar blue flower spikes, and sanicle, an unrelated plant, shares an old common name. Check the botanical name on seed and plants.

Common problems

No seedlings. Usually seed sown too deep, allowed to dry, or held in a hot tray; see Germinating the seed and its list, When nothing comes up.

Tall, pale, floppy seedlings. Too little light on a windowsill stretches them, so move trays to brighter light and turn them daily. Read more

Yellow-green plants losing their lower leaves. Drought stress in a long dry spell; see Three mistakes that matter.

Tiny leaves and short spikes. Frequent mowing or grazing keeps it as a dense mat with small leaves, which is normal in a lawn.

Plants dying out after a few years. Individual plants are often short-lived, so let a few spikes seed, or divide young runners to keep the patch going.

Seedlings everywhere. Pull strays while small, and deadhead as Trimming and Deadheading describes. Read more

Pests and diseases

Selfheal has no serious pest or disease recorded, so trouble is most likely at the seedling stage.

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

Common garden snail (Cornu aspersum). This snail, introduced from Europe, damages seedlings and is most active at night and after rain. Hand-pick it by torchlight on damp evenings. Read more

Grey field slug (Deroceras reticulatum). It feeds on the surface at night and becomes active after the autumn break, leaving shredded leaf edges. Hand-pick it as for snails. Read more

Prevention first

• Keep seed trays clear of rain and hose splash, which spread damping off.
• Water trays from below, and let the surface breathe between waterings.
• Plant out sturdy seedlings rather than tiny ones where slugs are common.
• Clear rocks, boards and dead plant material from around young plants, where slugs and snails shelter by day.

Tips

1. Plant a patch where a garden tap drips or a downpipe drains: selfheal thrives on the extra moisture.
2. Save seed by shaking spikes that have just turned brown over a paper bag: raindrops striking the ripe heads flick the seed out.
3. Edge the patch with a mowing strip or a sunken garden edge, so creeping stems stay where you want them.