Field penny-cress

How to recognise it

Habit

Hairless, pale green annual, 10–60 cm, with a straight stem branched at the top. Germinates in autumn or spring.

Leaf

Lower leaves short-stalked and soon gone; stem leaves oblong, entire or coarsely toothed, clasping the stem with two arrow-shaped lobes. Smells of garlic when crushed.

Flower

Small, 4–6 mm, white, with four petals, in clusters at the stem tips. Flowers mainly from April to August.

Fruit/Seed

Flat, round pods of 1–1.8 cm with a broad wing and a deep notch at the top; green at first, straw-yellow when ripe. They contain dark brown seeds with fine concentric ridges.

Roots

A thin taproot; the plant is easy to pull up.

Confusion with

Field pepperwort is greyish and hairy, with much smaller fruits. Shepherd’s-purse has triangular, heart-shaped fruits and a rosette of cut leaves. You know field penny-cress at once by the large, round ‘coins’ and the garlic smell.

Flowering: April–August

Why grow it?

• Flowers from April onwards, giving nectar and pollen to hoverflies, flies and small bees.
• Each plant makes plenty of seed: food for seed-eating farmland birds such as finches and sparrows.
• The coin-shaped fruits are decorative, also in a bunch of wild flowers.
• A characteristic plant of the old cornfield flora, showing how richly fields used to flower.
• A weed with a future: researchers are breeding field penny-cress into a new oilseed crop that covers the soil in winter.

Field penny-cress: where does it grow best?

• In the wild in arable fields, vegetable gardens, waste ground, ruderal places, verges and along railways.
• Full sun; open, cultivated soil.
• Rich, moderately moist loam or clay, also limy.
• In the garden: in a cornfield flower border, a vegetable garden or a sunny patch that you lightly cultivate every year.

Goes well with

• Common poppy: Red beside the white, on the same rich arable soil.
• Cornflower: Blue flowers in a cornfield flower border.
• Scented mayweed: Small white daisies with yellow centres, also a cornfield plant.
• Field pansy: Low and pale yellow, on the same open soil.

Field penny-cress: when and how to plant it?

1. Usually field penny-cress appears by itself on cultivated, rich soil; the seed stays viable in the soil for years.
2. If you want to sow it, use seed of native origin and sow in September–October or March–April where it is to grow.
3. Sow thinly on loosened soil, rake in lightly and firm.
4. Thin to 10–20 cm between plants.
5. Keep the soil moist until germination.
6. Never dig up plants in nature reserves or from other people’s fields.

Care

Water

Not needed.

Feeding

Not needed; on rich soil it already grows well.

Weeding

In the vegetable garden or among crops, pull or hoe young plants before they flower; the roots are shallow.

Letting it seed

Let a few plants ripen for the birds and for a new generation; each plant makes plenty of seed.

Cultivating

As a cornfield plant it needs open soil: lightly turn the border every year.

Tip: Pick a few stems with green, round fruits for a bunch of wild flowers: the ‘coins’ stay attractive for a long time. Do not crush the leaves, or your bunch will smell of garlic.

Pruning and mowing

When: Not needed: it is an annual that dies after setting seed.

How:

• Pull plants before the fruits turn straw-yellow if you do not want seedlings.
• Leave a few plants standing until the birds have eaten the seed.
• Dead plants can go on the compost heap, as long as they no longer carry ripe seed.

Pruning calendar and basic rules

Propagation

Seed

The pods ripen from June to September. Pick them when straw-yellow, let them dry further and sow in autumn or spring.

Field penny-cress: how does it get through the winter?

Hardy to −20 °C.

• Plants that germinate in autumn overwinter as a small rosette and flower early in spring.
• The rosettes are fully hardy.
• The seed stays viable in the soil for many years and germinates as soon as you cultivate the ground.

Diseases and pests

• Self-seeding: One plant makes plenty of seed that lasts for years in the soil. Weed before the fruits ripen.
• Flea beetles: Small holes in the leaves caused by flea beetles. Harmless for a wild plant.
• Brassica diseases: As a member of the cabbage family it can help keep diseases of brassicas, such as clubroot, going. Weed it out in a vegetable garden with cabbages.
• Garlic-tasting milk: Cows that eat it give milk that tastes of garlic. Keep it out of grassland and hay for dairy cattle.

Through the year

• March: Overwintered rosettes grow; seedlings appear on cultivated soil. Sowing possible.
• April: First small white flowers.
• May: Flowers and first green ‘coins’.
• June: Fruits turn straw-yellow; in the vegetable garden weed before they ripen.
• July: Seed ripens. Leave a few plants for the birds.
• August: Last flowers; the plants die.
• September: Sow for overwintering plants. Lightly cultivate the soil.
• October: Autumn seedlings form small rosettes.

Did you know?

• The name penny-cress refers to the round fruits, which look like coins.
• In North America, where it was introduced, field penny-cress is being bred into a new oilseed crop that can grow in winter between other crops.
• Thlaspi comes from a Greek word meaning to flatten, after the flat fruits.