Siberian Culver's root

Siberian Culver's root: how do you recognise it?

Habit

Upright, compact clump about 1.5 m tall and 60 cm wide, with sturdy, unbranched stems.

Leaves

Narrow, lance-shaped and toothed, in whorls of usually 4–7 leaves around the stem; dark green.

Flowers

Long, slim spikes of small lavender-blue flowers with protruding stamens, from July to September.

After flowering

The brown seed spikes remain into winter and stay attractive for a long time.

Roots

A sturdy rootstock: the clump spreads slowly and stays good for years in the same spot.

Flowering: July–September · Plants: March–May and September–October · Pruning: February–March

Why grow it?

• A slim, upright accent 1.5 m tall that takes little space and usually needs no support.
• Flowers from July to September, when many other perennials have finished.
• Bees, bumblebees and butterflies readily visit the flower spikes.
• Fully hardy and long-lived: the clump grows bigger and better every year.
• The seed spikes stand through winter and give structure to the border; it is also good as a cut flower in a bouquet.

Siberian Culver's root: where does it grow best?

• Full sun to light partial shade: it flowers best in sun, but stays fresher in partial shade.
• Humus-rich, moisture-retentive soil: loam, clay or peaty soil, acid to neutral.
• Best evenly moist to wet; in dry soil it stays smaller and flowers less.
• A sheltered spot is ideal, although the sturdy stems do not break easily.
• Allow 50–60 cm between plants.

Light

Sun and partial shade

Soil type

Loam, clay or peat

Acidity

Acid or neutral

Moisture

Normal or wet

Size

1.5 m tall, 0.6 m wide

Hardiness

Hardy (to -35 °C)

Goes well with

• Border phlox: Flowers at the same time and likes the same moist soil.
• Coneflower: Its round pink flowers contrast with the slim, blue spikes.
• Sneezeweed: Warm yellows, oranges and reds next to the cool lavender blue.
• Purple moor grass: A light ornamental grass that softens the stiff, upright spikes.
• Bergamot: Flowers at the same time and also attracts bees and butterflies.

Siberian Culver's root: when and how to plant it?

Plant in March–May and September–October.

1. Plant in March–May or in September–October, when the soil is neither frozen nor waterlogged.
2. Dig a hole twice as wide as the pot and mix in a few spadefuls of compost.
3. Set the plant at the same depth as in its pot, with the shoots just above the soil.
4. Keep 50–60 cm between plants and water in thoroughly straight away.
5. Spread a layer of leaf mould around the base and water in dry spells during the first year.

Care

Water

Keep the soil moist. In dry summers water generously at the base, especially in the first year.

Feeding

In spring, a layer of compost or a little organic fertiliser. On poor soil one extra feed in June is enough.

Mulching

A layer of compost or leaf mould in April keeps the soil cool and moist.

Support

Usually not needed. In partial shade or on very rich soil it can flop: put a support in place in spring.

Spent spikes

Leave them standing: they look good in autumn and winter. For a tidy border, cut them off after flowering.

Dividing

Usually only needed after 8–10 years, when the centre of the clump goes bare.

Tip: Leave the clump undisturbed for years: it grows slowly but improves every year. Mark the spot with a cane, because it only appears late in spring.

Siberian Culver's root: when to prune it?

Pruning months: February–March.

When: In February–March, before the new shoots appear above ground.

How:

• Cut all dry stems from last year down to just above the ground.
• Use sharp secateurs and put the stems on the compost heap.
• When cutting flowers for a bouquet, cut the stem just above a few whorls of leaves.

Caution: Do not leave it too late: young shoots can be damaged among the old stems.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Division

In March–April or in September: cut the clump with a spade into pieces with at least three shoots and roots each. Replant at once and water.

Sowing

The seed needs light to germinate and a cold spell. Sow in autumn on the surface of seed compost, do not cover it, and leave the tray outdoors over winter. Seedlings appear in spring and take a few years to flower.

Cuttings

In May: take young shoots of 8–10 cm with a piece of rootstock and insert them in moist seed compost.

Siberian Culver's root: how does it get through the winter?

Hardy to −35 °C.

• Fully hardy, down to about −35 °C: no protection is needed in Belgium.
• Leave the seed spikes until pruning in February–March; with frost on them they make a lovely winter sight.
• The shoots appear late in spring. Mark the spot with a cane so you do not tread on it or plant something else there.

Diseases and pests

• Slugs: Young shoots are nibbled in spring. Pick them off, put a barrier of coarse material around the clump, and be especially watchful in the first year.
• Powdery mildew: White powder on the leaves in a dry, stuffy summer. Space plants well, water at the base and cut off affected leaves.
• Wilting leaves: Brown leaf edges or limp foliage point to drought. Mulch and water generously.
• Flopping: On soil that is too rich or in too much shade it grows long and floppy. Feed less, give more light or add a support.

Through the year

• February: Cut down old stems (can be done until March).
• March: Cut back to the ground. Apply compost. Planting and dividing are possible from now on.
• April: Plant and mulch. Watch for slugs on the first shoots.
• May: Plant. Add a support if needed. Take cuttings.
• June: Water in dry spells. Feed on poor soil.
• July: Flowering begins. Bees and butterflies visit. Water in dry spells.
• August: Full flower. Cut flowers for a bouquet.
• September: Late flowering. Plant or divide. Let the seed ripen.
• October: Plant. Sow in a tray outdoors. Leave the seed spikes standing.
• November: Resting. The seed spikes decorate the border.
• December: Resting. Mark the position of the clump.

Good for wildlife

Bees

Nectar and pollen for honeybees and wild bees.

Butterflies

Nectar for butterflies.

Did you know?

• The name Veronicastrum means roughly ‘resembling Veronica’: the plant was once classed with the speedwells (Veronica).
• The leaves are arranged in tiers, in whorls around the stem, which gives the plant the look of a candelabra.
• Veronicastrum virginicum from North America is the better-known relative in gardens; the Siberian species is closely related to it.