Large bitter-cress

How to recognise it

Habit

Perennial of 20–60 cm with creeping, rooting runners and ascending stems that are hairless to slightly hairy.

Leaf

Pinnate, with 2–5 pairs of oval to angular, slightly toothed leaflets and a slightly larger end leaflet; also up the stem. No basal rosette at flowering time.

Flower

White flowers of 1–1.5 cm in a loose cluster, with four petals and strikingly violet anthers, from April to June.

Fruit/Seed

Narrow, upright pods of 2–4 cm that burst open when ripe and fling out the seeds.

Roots

A creeping rhizome and runners that root at the nodes.

Look-alikes

Cuckooflower has lilac to white flowers with yellow anthers and a rosette of leaves at the base; it grows more often in open grassland. Watercress has smaller white flowers with yellow anthers, a hollow stem, and flowers later, from May to September.

Flowering: April–June · Pruning: July

Why grow it?

• Food plant for the caterpillars of the orange-tip and the green-veined white, which lay their eggs on the flower stalks and leaves.
• Early nectar and pollen in April–May for bees, hoverflies and butterflies.
• One of the few flowering plants for wet shade: beside a stream, spring or pond under trees.
• A typical plant of springs and seepage: where it grows, clean groundwater often comes to the surface.
• With its creeping stems it forms a loose green mat that covers a wet bank.
• It flowers after marsh-marigold and before the tall summer plants: a sea of white flowers in the wet spring woodland.

Large bitter-cress: where does it grow best?

• In the wild beside springs, streams and ditches, in seepage zones and alder carr, often in trickling water.
• Also in wet, shady hay meadows and tall-herb vegetation in stream valleys.
• In the garden: partial to full shade; in sun only if the soil stays wet all the time.
• Wet to boggy, humus-rich soil: sand, loam or clay, moderately acid to chalky.
• Ideal at a pond edge, in a marsh zone or along a ditch, down to a few centimetres under water.

Goes well with

• Marsh-marigold: Yellow flowers in March–April on the same wet bank, just before the bitter-cress.
• Opposite-leaved golden-saxifrage: A low, golden-green mat for the wettest shady spots near a spring.
• Water forget-me-not: Sky-blue little flowers at the water’s edge, from May into autumn.
• Cuckooflower: Another orange-tip food plant, for the sunnier wet grassland next to it.
• Meadowsweet: Tall, fragrant summer flowers that fill the spot once the bitter-cress has finished.

Large bitter-cress: when and how to plant it?

1. Never dig up plants in the wild: buy them from a nursery for native plants or pond plants.
2. Plant in March–April or in September–October in wet soil at the edge of a pond, stream or ditch.
3. Space the plants 25–30 cm apart; with their runners they fill the gaps by themselves.
4. You can also sow: sow fresh seed in summer or autumn on wet, open ground, or in a tray standing in a dish of water.
5. After planting, keep the soil wet at all times: drying out is the biggest danger.
6. Leave some tall vegetation around it, so that orange-tip caterpillars can pupate nearby.

Care

Water

Never let it dry out. By a pond or stream nature takes care of this; in a boggy spot in the border, water in dry summers.

Feeding

Not needed. Fallen leaves and leaf mould are enough.

Spreading

It spreads with creeping runners but stays manageable: pull or dig out pieces that have spread too far in spring.

Mowing

Mow a wet hay meadow only after the seed has set, from July onwards, and remove the cuttings.

Spare the caterpillars

Leave the stems and tall vegetation standing in summer: orange-tips often pupate on nearby stems and overwinter as a chrysalis.

Tip: Plant large bitter-cress in the shade and cuckooflower in the sunny wet grass beside it: that way the orange-tip finds food plants all over your garden.

Pruning and mowing

Pruning months: July.

When: Little needed. In July, cut off the withered flower stems if you like, once the seed has dropped.

How:

• Cut the old flower stems just above the leaves.
• Leave some of the stems and the vegetation around the plant for overwintering orange-tip chrysalises.
• Remove runners that have spread too far in spring or autumn.

Caution: Do not mow or cut in April–June: the flower stems then carry orange-tip eggs and caterpillars.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Division

In March–April or September: dig out a piece of the mat with roots and runners and replant it straight away in a wet spot.

Runners

Creeping stems root at the nodes. Cut off a rooted piece and replant it.

Seed

Sow fresh seed in summer or autumn on wet ground and keep it moist at all times.

Large bitter-cress: how does it get through the winter?

Hardy to −25 °C.

• The flower stems die back; the plant overwinters with its creeping rhizomes, and in mild winters a few green leaves often remain.
• Fully hardy, to about −25 °C; wet ground near a spring rarely freezes deeply.
• Leave the tall vegetation around it: orange-tip chrysalises overwinter on nearby stems.

Diseases and pests

• Drying out: Limp or yellow leaves in summer. Choose a spot that is always wet, or water.
• Slugs and snails: They nibble young leaves in spring. Usually not a problem; toads, thrushes and hedgehogs help.
• Caterpillars: Orange-tip or green-veined white caterpillars eat the pods and leaves. Leave them: that is why you grow it.
• Being crowded out: In tall vegetation that is too dry or sunny it disappears under nettles and grasses. Keep the spot wet and mow around it.

Through the year

• March: Plant or divide. New leaves appear.
• April: Flowering begins. Orange-tips are on the wing and lay their eggs.
• May: Full flower. Look for the orange eggs and green caterpillars on the flower stalks.
• June: Last flowers; the pods ripen.
• July: The seed is flung from the pods. Cut off withered flower stems if you wish.
• August: Water if the spot dries out.
• September: Plant or divide. Remove runners that have spread too far.
• November: Rest. Leave tall vegetation for overwintering chrysalises.

Did you know?

• The species name amara means bitter in Latin: the leaves taste more bitter and sharper than watercress.
• The scientific name of the orange-tip, Anthocharis cardamines, refers to the bitter-cresses, its main food plants.
• The violet anthers are the quickest clue: they let you tell it at a glance from white cuckooflowers and watercress.