Knotted cranesbill

Knotted cranesbill: how do you recognise it?

Habit

A loose, slightly spreading clump 30–40 cm tall and up to 50 cm wide, which slowly widens.

Stems

Thin, with distinctly swollen nodes where the leaves are attached.

Leaves

Glossy mid-green, three- to five-lobed and toothed.

Flowers

Funnel-shaped, 2–3 cm across, lilac to pink with dark veins and notched petals, from May to September.

Roots

Creeping rhizomes that spread gently.

Flowering: May–September · Plants: March–April and September–October · Pruning: March

Why grow it?

• One of the few plants that flower for months in dry shade.
• A long flowering season from May to September, long after most shade plants have finished.
• Glossy, fresh leaves that brighten dark corners.
• It forms a loose ground cover under trees and shrubs without becoming invasive.
• Bees and hoverflies visit the flowers all summer.

Knotted cranesbill: where does it grow best?

• Partial or full shade: under trees, next to shrubs or on the north side of a wall.
• Sand, loam or clay, acid, neutral or chalky; preferably with some leaf mould.
• Dry to normal soil; once established it copes well with drought under trees.
• Plant 35–40 cm apart, in groups, for a loose ground cover.

Light

Partial shade and shade

Soil type

Sand, loam or clay

Acidity

Not fussy

Moisture

Dry or normal

Size

0.4 m tall, 0.5 m wide

Hardiness

Hardy (to -30 °C)

Goes well with

• Ferns: Fine fronds beside the glossy cranesbill leaves, in the same shade.
• Barrenwort: A tough, low ground cover that flowers in April, before the cranesbill starts.
• White wood aster: Takes over the flowering in August, in the same dry shade.
• Wood spurge: Lime-green spring flowers and evergreen leaves beside the lilac blooms.

Knotted cranesbill: when and how to plant it?

Plant in March–April and September–October.

1. Plant in March–April or September–October; in autumn the soil under trees is moister and it establishes more easily.
2. Make a planting hole between the tree roots and mix in some leaf mould or compost.
3. Set the plant at the same depth as it was in its pot and firm the soil.
4. Space plants 35–40 cm apart.
5. Water in well straight away and keep the soil moist in dry spells during the first year.
6. Mulch with leaf mould.

Care

Watering

In dry weather during the first year; after that it manages, even in dry shade.

Feeding

A layer of leaf mould in March is enough.

Mulching

Leave fallen leaves in place: they turn into leaf mould by themselves.

Spent flowers

Cut off the spent stems if you want fewer seedlings.

Seedlings

It self-seeds gently. Leave seedlings where they fit or move them in spring.

Tip: Plant it in a group under trees and let the seedlings be: after a few years you will have a loose, flowering ground cover where there used to be bare soil.

Knotted cranesbill: when to prune it?

Pruning months: March.

When: Pruning is hardly needed. In March, cut away the old, withered foliage before the new shoots appear.

How:

• In March, cut all old leaves and stems down to just above the ground.
• In summer, cut off spent flower stems if you want fewer seedlings.
• Leave the foliage in autumn: it protects the roots.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Division

In March–April or September: cut off a piece with rhizome and shoots and replant it elsewhere.

Seedlings

In spring, lift seedlings around the plant with a little soil and replant them. White cultivars do not always come true.

Seed

Sow ripe seed in summer or autumn in a pot outdoors.

Knotted cranesbill: how does it get through the winter?

Hardy to −30 °C.

• Hardy to about −30 °C: in Belgium it needs no protection.
• Most of the foliage dies back in winter; it reshoots in March.
• In a pot it overwinters outdoors, as long as water can drain away.

Diseases and pests

• Slugs: They eat young leaves in spring. Pick them off in the evening.
• Powdery mildew: White powder on the leaves in severe drought. Water and cut off affected leaves.
• Too many seedlings: In a small border they can become too numerous. Cut off spent stems and weed out surplus seedlings while young.
• Rust: Brown or orange spots under the leaves. Cut off affected leaves and give the plant a little more space.

Through the year

• March: Cut away old foliage. Plant or divide. Add leaf mould.
• April: Plant. Move seedlings. Watch for slugs.
• May: Flowering begins.
• June: Full flower. Bees on the flowers.
• July: Flowering. Water in long dry spells.
• August: Flowering. Cut off spent stems if you want fewer seedlings.
• September: Last flowers. Plant or divide.
• October: Plant. Leave fallen leaves in place.

Good for wildlife

Bees

Nectar and pollen for honeybees and wild bees.

Did you know?

• Nodosum means ‘knotted’: the stems have swollen nodes where the leaves are attached.
• The dark veins on the petals act as guides that lead insects to the nectar.
• In Britain it has become naturalised in woodland in a few places.