How to Grow Valerian in Australia

Valerian (Valeriana officinalis) is a hardy perennial grown for its tall heads of scented summer flowers, which draw bees, and for its strong-smelling roots. It belongs to the honeysuckle family, Caprifoliaceae, and its flowers are pale pink to white. It reaches about 1.5 m in cool, moist gardens, dying down each winter and returning in spring. The step that decides success comes first: the seed needs light, so sow it on the surface, uncovered or under a bare dusting of mix.

Three mistakes that matter

1. Burying the seed. Valerian seed needs light to germinate, so seed buried under mix can leave a tray bare. Press it onto the surface and leave it uncovered, or give it at most a dusting of mix, as Germinating the seed describes.
2. Sowing old seed. The seed is short-lived and is usually no longer viable after about two years, whatever treatment it is given. Sow a fresh packet, and keep spare seed cool and dry until the next sowing.
3. Letting the soil dry out. A seedbed that dries even once can lose its seedlings, and established clumps wilt and stall in a dry summer. Keep the soil evenly moist, mulch it, and give afternoon shade where summers run hot.

When to plant

Valerian seed germinates best when the mix sits at 15 to 20°C. Sow from late winter into spring, or in autumn where winters are mild. Plants are frost hardy, so seedlings raised under cover can go out two to four weeks before the last frost. One sowing lasts for years, because each clump can be divided.

Seed sown into summer heat dries out on the surface, so in warm zones wait for the cooler weeks around Anzac Day. In cool districts, sow under cover in late winter and plant out once the soil can be worked.

Site, soil and setup

Wild valerian grows in the moist woodlands of Europe and western Asia. In a garden, copy that with rich soil that stays damp but never sits wet, in a spot the clump can keep for years.

As a perennial, valerian sits outside the yearly vegie rotation. When the roots come out, follow it with peas or beans, as commercial growers do.

Container growing

A pot suits valerian where garden soil dries out fast. Give one plant a pot at least 40 cm wide, about 28 L, because a clump spreads to about 45 cm by its second year. Use a quality potting mix with compost worked through. Pots change the shape of the roots, so move a clump grown for roots into a bed after its first season. The store sells the species as valerian seeds, with no compact varieties.

• Water: whenever the top of the mix feels dry, until water runs from the drainage holes.
• Feed: worm casting liquid diluted to weak tea colour, fortnightly from spring to autumn.
• Position: morning sun and afternoon shade, sheltered from wind, which catches tall stems in a pot.
• Winter: the top dies down; keep the mix just moist until new leaves appear in spring.

Germinating the seed

Valerian seed asks for two things rather than a long treatment. The first is light, because the seed germinates in response to it, so it belongs on the surface of the mix. The second is freshness: the seed is short-lived, and viability falls away within about two years.

This is not a hard seed. In the Seed Information Database, 75 per cent of a sample germinated in light with warm days and cool nights. Manitoba's growers report about 80 per cent from direct sowing, over about five weeks. In a tray, seedlings usually appear in 14 to 28 days. Sow two or three seeds for each plant you want.

The sources disagree about chilling. The store's listing suggests 2 to 4 weeks in the fridge for even germination, but Manitoba found stratification did not improve it. Try a chill only with seed that has been slow before.

When nothing comes up

• Sown too deep. Seed under more than a dusting of mix sits in the dark; sow again on the surface.
• Surface dried out. One dry afternoon can kill germinating seed. Cover the tray with clear plastic or glass and mist it daily, then take the cover off once most seedlings are up.
• Too cold. Below the range When to plant gives, germination slows; move the tray somewhere warmer or onto a seedling heat mat.
• Old seed. Seed more than about two years old, or stored somewhere warm and damp, may not come up at all; start with a fresh packet.
• Mouldy stratification bag. Too much water rots seed in the fridge; use mix that is only just damp and check the bag weekly.
• Given up too soon. Outdoor sowings are slower than trays; wait six weeks before sowing again.

Sowing Seeds

Start valerian in a punnet or tray under cover, or sow it straight into a fine seedbed, from fresh seed pressed onto the surface.

Starting under cover

• Fill punnets with fine seed raising mix, water it, and press two or three seeds onto each cell.
• Leave the seed uncovered, or dust it with no more than 1 to 2 mm of mix.
• Keep the tray in bright light out of harsh midday sun, at the temperature When to plant gives.
• Water from below or with a mister so the seed stays put and the surface stays damp.
• Expect seedlings in 14 to 28 days, and prick them out into their own pots once they are large enough to handle.

Sowing direct

Direct sowing works in a fine, weed-free seedbed that can be watered every day. Scatter the seed thinly and press it in with a flat board. Water with a fine rose until seedlings show, which can take about five weeks outdoors. Thin them to the final spacing once they carry a few true leaves.

Transplanting

• Harden off seedlings first (hardening off: a week or so of longer daily spells outdoors to toughen them).
• Plant them 30 to 45 cm apart, with the crown level with the soil surface.
• In frosty districts, plant out at the time When to plant gives.
• Water in well, then mulch around the plants without piling mulch against the crowns.

Care by growth stage

Steady moisture decides valerian far more than feeding. Compost in the bed and a light spring side-dressing carry it, because valerian needs little fertiliser.

If growth stalls in poor soil, a light application of all-purpose controlled release granular (NPK around 14-5-10) scratched into the soil can help. In windy spots, push a stake in beside each clump in spring. Tie the flowering stems to it loosely with soft ties as they grow.

Cutting Back

Valerian self-seeds freely, and removing its flowers puts more growth into the roots.

• Deadhead the flower heads as they fade, before the feathery seed forms and blows about the garden.
• On plants grown for roots, cut the flower stems off early, so growth goes into the rhizome (a short underground stem).
• Cut the whole plant back after flowering to tidy it.
• Cut the dead stems to ground level in autumn once they yellow.
• Lift and divide clumps every three years or so, in spring or autumn, because crowded clumps lose vigour.

Pull any self-sown seedlings while they are small, particularly near bushland, because valerian has escaped gardens overseas.

Companion planting

Pair valerian with plants that want the same moist soil, and keep it away from herbs that want dry ground or that run.

Grows well with

• Sorrel, which wants the same evenly moist soil and afternoon shade in hot summers.
• Chives, whose low clumps fill the ground in front of valerian's tall, bare stems.

Keep apart

• Mint, whose runners cross a bed and push into the valerian clump.
• Lavender and thyme, which want lean, sharply drained soil and little water, the opposite of a valerian bed.

Harvesting Roots

Lift the roots in the second year, from autumn into early winter as the tops die down, or after the first frosts in cool districts.

• Choose a cool morning, so the roots do not dry out as they come up.
• Cut the stems away, then loosen the whole clump with a garden fork from well outside the crown.
• Lift the clump and shake off the soil, keeping the fine roots, which are part of the harvest.
• Break off a piece of crown with buds and replant it, so the bed keeps going.
• Wash the roots clean and cut thick pieces smaller, so they dry evenly.

Dry the roots in the shade with a gentle airflow, below about 40°C. They smell far stronger as they dry, so a shed or a veranda suits better than the kitchen. Store dried roots in an airtight container somewhere cool and dry, where they keep for two years or more.

In summer, the flower heads also make scented cut flowers for a vase.

Traditional use and history

The name valerian comes from the Latin valere, to be in good health. Older names recorded for it include setwall, garden heliotrope, St George's herb and phu. The plant grows wild from Europe to north-west Iran and has escaped gardens in North America. The IUCN Red List has not assessed it.

Several related plants are sold under the same English name, among them Indian valerian (Valeriana jatamansi) and Mexican valerian. Folklore has the Pied Piper of Hamelin carrying valerian to lure the rats and the cats. The link with cats, at least, is real: in one study, about half of 100 domestic cats responded to dried valerian root.

Safety

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

Red valerian (Centranthus ruber) shares the name but is a different plant. It has fleshy, blue-green, mostly undivided leaves and spurred red, pink or white flowers, and it thrives on dry, rocky or limey ground. True valerian has leaves divided into many paired, toothed leaflets and wants moist soil. Red valerian has escaped gardens onto granite outcrops, roadsides and coastal dunes in southern Australia, so check the botanical name before planting.

Common problems

Stems flop over. Heavy shade and wind both make tall flowering stems lean. Stake them early, as Care by growth stage describes, or move the clump into more sun.

Seedlings everywhere. Flower heads left to ripen scatter feathery seed through the garden. Deadhead before the seed forms, as Cutting Back describes. Read more

Cats and rats in the bed. Both are drawn to valerian, and cats roll on or dig out young plants. Protect new plantings with a wire cage until they establish. Read more

A tired clump with a bare centre. Crowded clumps lose vigour after a few years. Lift and divide them, replanting the young outer pieces.

Leggy seedlings. Long, pale stems that flop over are stretching for light, and warmth after emergence makes it worse. Move the tray to the brightest spot and keep it cooler. Read more

Pests and diseases

Established valerian is rarely troubled, so most losses happen at the seedling stage or in soil that stays wet.

Common garden snail (Cornu aspersum) and grey field slug (Deroceras reticulatum). Both graze seedlings to stalks overnight in damp weather, leaving a slime trail. Hand-pick them after dark, and plant out sturdy potted seedlings rather than tiny ones. Read more

Aphids (family Aphididae). Small sap-sucking insects cluster on soft new growth in warm spring weather. A firm jet of water or an insecticidal soap spray knocks them back, and ladybirds follow. Read more

Damping off (Pythium and Rhizoctonia). Seedlings collapse at the base while their leaves still look fresh, in wet, crowded, cold trays. Use clean trays and fresh mix, and water from below. Read more

Root rot (Rhizoctonia and Phoma fungi, recorded on valerian overseas). Roots darken and rot and the clump declines, most often in waterlogged soil. Lift and bin affected plants rather than dividing them, and replant with fresh seedlings in better-drained ground.

Prevention first

• Sow in clean trays with fresh seed raising mix.
• Keep the soil moist but never waterlogged, and raise the bed where drainage is poor.
• Check seedlings and new plantings for snails and slugs after rain and at night.
• Clear dead stems and leaves in autumn so pests have less shelter.

Tips

1. Mix the fine seed with a pinch of dry sand before sowing, so it spreads thinly and you can see where it lands.
2. Label the bed clearly, because the clump disappears below ground each winter and is easy to dig into by mistake.
3. Plant a few clumps for flowers and a separate one for roots, then cut the flower stems off the root clump only.