Kidney vetch

How to recognise it

Growth habit

Short-lived, often biennial to perennial plant with sprawling to ascending stems of 10–40 cm.

Leaf

Pinnate, with a few pairs of narrow leaflets and a larger end leaflet; the lowest leaves sometimes have only one large end leaflet. Silvery-hairy, especially beneath.

Flower

Yellow, sometimes orange or reddish pea flowers in dense, round heads of 2–4 cm, often in pairs; beneath each head a deeply cut, hand-shaped bract. From May to August.

Fruit/seed

A small one-seeded pod, hidden in the persistent, inflated calyx.

Roots

A taproot with nodules in which bacteria fix nitrogen.

Confusion with

Bird’s-foot trefoil also has yellow pea flowers, but in loose rings without woolly calyces. Black medick has small yellow balls and leaves with three leaflets.

Flowering: May–August · Pruning: September

Why grow it?

• In our region practically the only food plant of the small blue, which lays its eggs in the flower heads.
• Bumblebees and other long-tongued bees draw nectar from the deep flowers.
• Root nodules fix nitrogen from the air, so it grows on poor soil where few other plants thrive.
• A lovely low flower for a dry rock garden, a gravel garden, a green roof or a poor verge.
• The woolly calyces give the flower heads a soft, silvery look, even after flowering.

Kidney vetch: where does it grow best?

• In the wild: chalk grassland, coastal dunes, dry verges, railway embankments, quarries and rocky slopes.
• Full sun: in shade it soon disappears.
• Dry, poor, well-drained soil; chalky sand, marl or gravel is ideal.
• It cannot stand competition from tall grasses: choose an open, poor spot, such as a gravel garden, a rock garden or a green roof.

Goes well with

• Wild marjoram: Purplish-pink flowers on the same dry, chalky soil.
• Salad burnet: Fine leaves and reddish flower balls, also at home in poor chalk grassland.
• Harebell: Blue bells among the yellow heads, on poor soil.
• Large thyme: A fragrant, low carpet for a gravel garden or a green roof.

Kidney vetch: when and how to plant it?

1. Buy seed of wild, ideally regional, origin or plants from a native plant nursery.
2. Sow in September–October or March–April, thinly and shallowly on bare ground, and press the seed in well.
3. Hard seed germinates better if you rub it lightly between sandpaper or soak it overnight in lukewarm water.
4. Plant pot-grown plants in spring, 20–30 cm apart; do not move them later, as they have a taproot.
5. Water only until the plants are established, and never feed.
6. Never dig up plants from the wild: kidney vetch has become rare in many places.

Care

Water

Only while establishing; never after that, as it loves drought.

Feeding

Never: in rich soil grasses overgrow it.

Mowing

Mow a poor meadow once a year, in September, after the seed has ripened, and remove the cuttings.

Letting it seed

Kidney vetch often lives only a few years. Let the seed ripen and keep small patches of bare soil where seedlings can come up.

Weeding

In spring, pull out pushy grasses around the plants.

Tip: Sow kidney vetch on a base of poor sand or crushed stone rather than garden soil: the poorer the soil, the longer it holds its own among the grasses.

Pruning and mowing

Pruning months: September.

When: Not needed; in a poor meadow, one cut in September.

How:

• Leave the faded heads until the seed is ripe.
• Then mow short and remove the cuttings, so the soil stays poor.
• In a rock garden you can cut off the faded stems in September; the leaf rosette remains.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Seed

Pick ripe heads in August–September, let them dry and sow in autumn or spring.

Self-seeding

On open, poor soil it self-seeds. Keep patches of bare soil free for seedlings.

Kidney vetch: how does it get through the winter?

Hardy to −25 °C.

• Overwinters as a small, green leaf rosette.
• Hardy to about −25 °C, but it rots on soil that stays wet in winter.
• Fully grown small blue caterpillars overwinter in the leaf litter beneath the plant.

Diseases and pests

• Disappearing: Short-lived and sensitive to competition. Keep the soil poor and open, and let seed fall.
• Rot: On wet, heavy soil the crown rots. Plant in gravel or sand.
• Slugs: They eat seedlings. Sow generously or protect the young plants.
• Rabbits: Rabbits like to graze it; in a garden with rabbits, put mesh over the young plants.

Through the year

• March: Sow on an open, poor spot. Pull grass away from the plants.
• April: Plant. Seedlings appear.
• May: Flowering begins.
• June: Full flower: bumblebees on the flowers. Small blues lay eggs in the flower heads.
• July: In flower. Do not water.
• August: Last flowers; the seed ripens.
• September: Collect seed. Mow and remove the cuttings. Autumn sowing.
• November: Green rosette; make sure no wet leaves stay lying on it.

Did you know?

• Vulneraria means wound-healing: the plant was once laid on wounds, which also explains its Dutch name wondklaver, wound clover.
• Small blue caterpillars live in the flower heads and feed on the developing seeds.
• There are forms with orange or red flowers; the colour can even vary within a single population.