How to Grow Skullcap in Australia

Skullcap is the shared name of two mint-family perennials (Lamiaceae), grown for their hooded blue to purple flowers and their place in herb gardens. They are Baikal skullcap (Scutellaria baicalensis) and American or blue skullcap (Scutellaria lateriflora). Baikal skullcap comes from sunny, dry grassland in Siberia, Mongolia and northern China. American skullcap grows wild in wet meadows and on stream banks across North America. Most failures start at sowing: American skullcap seed usually wants a cold, moist spell and light, and Baikal seed sprouts best chilled and covered.

Three mistakes that matter

1. Skipping the cold spell and burying the seed. American skullcap seed usually needs weeks of cold, moist conditions before it wakes, and tiny seed sown deep stays in the dark. Chill it as Germinating the seed describes and barely cover it.
2. Planting both in the same bed. Baikal skullcap rots in soil that stays wet, and American skullcap wilts and browns in dry, sunny ground. Give each its own spot, as the table in Site, soil and setup sets out.
3. Digging Baikal roots too early. A first-year root is thin and small. Leave the plant in the ground for at least two years, and up to four, before lifting it, as Harvesting Stems and Roots explains.

When to plant

Skullcap seed germinates in warmth, about 18 to 25°C, once any cold spell it needs is over. Sow outdoors in autumn and let winter do the chilling, or chill seed in the fridge and sow it in spring. Both are perennials, so one sowing lasts for years.

In frosty districts, keep spring trays under cover and plant out after the last frost. Coastal winters, from Perth to Sydney, are often too mild to chill seed outdoors, so use the fridge there.

Site, soil and setup

Two other names, mad dog skullcap and Virginia skullcap, belong to American skullcap, though they sometimes appear against Baikal seed.

For Baikal skullcap, dig in a 5 cm layer of compost and build a mound or raised bed if the ground stays wet after rain. For American skullcap, dig in a 5 cm layer of compost or well-rotted manure 4 to 6 weeks ahead, then mulch to hold moisture. Where a pH test reads below the range, dig in garden lime at 100 to 200 g per square metre 4 weeks before planting. Give both a permanent bed outside the vegetable rotation.

Container growing

Pots suit both plants: they keep American skullcap from creeping through a bed and let Baikal skullcap stay dry through wet spells. Give one plant a pot at least 30 cm wide, which holds about 13.5 L, and use a quality potting mix. For Baikal skullcap, mix in one part coarse sand to four parts potting mix for drainage.

• Water: Baikal skullcap when the top 2 cm of mix is dry; American skullcap daily in warm weather, so the mix never dries out.
• Feed: worm casting liquid diluted to weak tea colour, fortnightly from spring to late summer.
• Position: full sun for Baikal skullcap; morning sun and afternoon shade for American skullcap.
• Saucers: leave one under American skullcap in summer, but never under Baikal skullcap.

Germinating the seed

American skullcap seed carries a dormancy that a spell of cold and moisture breaks, as a winter outdoors would. The seed is tiny, around 2,500 to the gram, and most sources sow it in light at the surface. Baikal seed is larger, around 560 to the gram, and two trials found it sprouts best in the dark. Fresh Baikal seed can germinate warm without a chill. Stored seed does far better after one, so chill any seed whose age you do not know.

Rates vary widely between seed lots. In one university trial, American skullcap seed chilled for one or two months gave only 1 to 2 per cent over 30 days. A Tasmanian trial's seed tested above 70 per cent, and some came up within four days, untreated. Growers who chill their seed report seedlings in about two to four weeks. Sow a whole 10-seed packet of American skullcap for even a few plants, and three Baikal seeds per plant wanted.

More on these methods is in Soaking, Scarification and Cold Stratification.

When nothing comes up

• Sown too deep. Tiny American skullcap seed under more than a dusting of mix stays in the dark; sow it again on the surface and press it in.
• No chill, or too short a chill. Unchilled American skullcap seed may sit dormant; give it 30 to 60 days in the fridge and sow again.
• Stratification bag dried out or went mouldy. Start again with mix that holds together when squeezed but drips no water.
• Too cold after the chill. Chilled seed needs warmth to sprout; move the tray indoors or onto a seedling heat mat.
• Old or warm-stored seed. Seed kept warm loses vigour; store packets in a sealed jar in the fridge.
• Given up too soon. Wait eight weeks before resowing, and leave an outdoor tray through a second winter, because some seed may still come up.

Sowing Seeds

Start skullcap in trays from treated seed, because the seedlings are small and easily lost in open ground.

Starting under cover

• Fill a tray with fine seed raising mix and water it before sowing.
• Scatter seed thinly and press it in; leave American skullcap bare or barely dusted, and cover Baikal seed with about 2 mm of mix.
• Keep the mix at the warmth When to plant gives, moist but not wet, under a clear lid.
• Lift the lid as soon as seedlings show, and thin crowded patches so air moves between them.
• Prick out (lift each seedling by a leaf into its own small pot) once seedlings can be handled.

Mixing the seed with a little dry sand makes it easier to spread (see How to Sow Tiny Seeds).

Sowing direct

Sow direct into a fine, weed-free bed in early spring with chilled seed, or in autumn where winter is cold enough to chill it. Scatter it shallowly, mark the row, and keep the surface damp until seedlings show. Thin the seedlings to 30 cm apart once they have several pairs of true leaves.

Transplanting

Seedlings reach planting size about six to eight weeks after sowing. Harden them off first (get them used to outdoor sun and wind over about a week), as hardening off seedlings describes. Plant them 30 cm apart, set American skullcap slightly deeper than it sat in the pot, and firm the soil around each one.

Care by growth stage

Water decides the crop far more than feeding: steady moisture for American skullcap, and restraint for Baikal skullcap. Neither needs rich feeding, and American skullcap is reported to be shorter lived in very rich soil.

If growth stalls in poor soil, a light application of all-purpose controlled release granular (NPK around 14-5-10) scratched in around American skullcap can help. Baikal skullcap needs nothing beyond compost at planting.

Cutting Back

Both skullcaps die back to the ground in cold winters and regrow from the roots in spring. Cutting back keeps them tidy and gives American skullcap fresh, leafy stems.

• Cut spent American skullcap stems to about 8 cm after flowering or harvest.
• Clear dead stems of both species to ground level in late winter, before new shoots appear.
• Deadhead Baikal skullcap flowers if self-sown seedlings are not wanted.
• Slice away American skullcap runners that stray beyond their bed with a spade.
• Divide crowded clumps of either species in spring, just before new growth begins; see Dividing Perennials.

Companion planting

Match each skullcap with plants that share its water needs, and keep spreading neighbours at a distance.

Grows well with

• Baikal skullcap with thyme, lavender and oregano, which want the same sunny, free-draining ground and little water.
• American skullcap with sorrel, which suits the same moist soil and part shade.
• American skullcap near wasabi in a damp, shaded corner, where both get the constant moisture they need.

Keep apart

• Mint, whose runners compete with American skullcap for the same damp ground.
• Comfrey, whose large leaves shade out and crowd both skullcaps.

Harvesting Stems and Roots

Cut American skullcap stems when the plant is in flower, in your calendar's first harvest window. Lift Baikal roots from plants two to four years old, in the second window once the tops die back, or in early spring.

• Pick American skullcap stems in the afternoon, once dew has dried, cutting about 8 cm above the ground.
• Take only a light cut in the first year; established plants give two cuts a season.
• Keep cut stems in the shade until you finish picking, so they do not heat up.
• Lift Baikal skullcap with a garden fork, working wide of the taproot to keep it whole.
• Wash the soil from the root, trim off the fine side roots, and dry it in an airy, shaded spot.
• Replant any Baikal crown pieces that carry buds.

Dry stems on a screen or rack in a well-ventilated, shaded place, covered at night so dew does not settle on them. Store the dried stems and roots in airtight, labelled jars in a cool, dark cupboard.

Traditional use and history

The genus name comes from the Latin scutella, a small dish, after the rim on the flower's calyx. The English name skullcap refers to the flower's likeness to a helmet.

Baikal skullcap in China

In Chinese the plant is huang qin, and in Japanese ogon. Huang means yellow, and qin is read as golden herb, after the colour of the root. The dried root was first recorded in the Shennong Bencaojing, the classic herbal of early China. Sources date that book to between about the first century BC and the third century AD.

Li Shizhen described the root again in the Bencao Gangmu, a work of the late sixteenth century. Traditional Chinese medicine classes it among the heat-clearing herbs, and the Chinese Pharmacopoeia lists it. Wild stands declined sharply over recent decades as demand for the root grew, so China lists it as a class III conserved medicinal plant. Large-scale farming of the root began there in the mid twentieth century.

American skullcap in North America

American skullcap had a place in the women's medicine of Native North American peoples. Late in the eighteenth century it entered American medicine against the hydrophobia of rabies. The name mad dog skullcap recalls that belief, which later proved false. It was listed in the United States Pharmacopeia from the mid nineteenth to the early twentieth century, and later in the National Formulary.

Safety

Both skullcaps are sold as seed for growing, and nothing here is advice to eat or take any part of either plant. Anyone thinking of using a plant should first seek advice from a qualified health practitioner.

Germander (Teucrium species), a plant linked to liver injury, has turned up in products sold as skullcap. Plants sold as American skullcap can also turn out to be a taller relative, Scutellaria altissima. True American skullcap carries its tiny flowers along one side of short sprays from the leaf joints, so check the flowers and the botanical name.

Common problems

Baikal plants yellow and collapse over winter. Cold, wet soil can rot the thick root, so move survivors to a raised, sandy bed or a pot.

American skullcap browns and wilts in summer. Dry soil and hot afternoon sun scorch a plant of stream banks, so mulch, water daily and give it afternoon shade. A wicking bed keeps the soil moist between waterings.

Spindly, pale seedlings. Too little light after germination stretches seedlings, so move the tray to bright light at once. Read more

American skullcap turning up across the bed. The plant spreads by rhizomes and runners, so dig out strays each spring and grow it in a pot where space is tight.

Pests and diseases

Skullcaps have few serious problems, and most trouble comes at the seedling stage or from the wrong soil moisture.

Aphids (Aphididae). Small green or yellow sap-suckers cluster on soft tips and leave distorted new growth and sticky honeydew. Knock them off with a strong jet of water, or spray insecticidal soap at the label rate on the undersides of leaves. Read more

Powdery mildew (Oidium and related fungi). A white powdery coating spreads across leaves in warm, humid weather. Water the soil rather than the leaves, remove the worst leaves, and spray 1 part full-cream milk to 10 parts water. Read more

Garden snail (Cornu aspersum). Snails, and slugs with them, feed at night and in wet weather and chew young transplants to stumps. Hand-pick them after dark, or trap them in shallow dishes of beer. Read more

Damping off (Pythium species and Rhizoctonia solani). Seedlings rot before they emerge or collapse at soil level soon after. Use fresh seed raising mix and clean trays, and water only enough to keep the mix moist. Read more

Grasshoppers (Orthoptera). Summer outbreaks strip leaves; plants kept evenly watered suffer less. Net prized plants in an outbreak and hand-pick in a quiet year. Read more

Prevention first

• Match the site to the species, so Baikal stays dry and American skullcap stays moist.
• Keep grass and weeds down around beds, removing the food and bare ground grasshoppers use.
• Water at the base in the morning, so leaves dry before night.
• Check seedlings and soft tips after dark for snails and aphids.

Tips

1. Label every stratification bag with the species and the date it went into the fridge.
2. Save Baikal seed from older plants, which set more viable seed as they age.
3. Lift only some Baikal plants in any one year, and leave the rest to grow on for a later harvest.