Hop trefoil

How to recognise it

Habit

Sprawling to ascending, branched annual, 10–30 cm, slightly hairy.

Leaf

Trifoliate; the leaflets are obovate, 5–10 mm, finely toothed at the tip. The middle leaflet sits on a clearly longer stalk. Oval stipules.

Flower

Rounded heads of 1–1.5 cm with 20–40 pale yellow to golden-yellow flowers; the standard petal is broad and furrowed lengthwise. Flowers from May to September.

Fruit/Seed

After flowering the flowers turn pale brown and fold over the small one-seeded pod: the head then looks like a miniature hop cone.

Roots

A thin taproot with nitrogen-fixing nodules.

Confusion with

Lesser trefoil has smaller heads with 3–15 flowers and a standard without furrows. Black medick has a tiny point at the tip of the leaflets and black, kidney-shaped pods. Large trefoil is bigger and has all its leaflets stalkless.

Flowering: May–September · Pruning: July and September

Why grow it?

• Flowers from May to September: small bees, bumblebees and hoverflies collect nectar and pollen from it.
• A neat little plant for a poor, flowery lawn or a dry verge, where it grows no taller than 10–30 cm.
• As a member of the pea family it fixes nitrogen through nodules on its roots.
• The pale brown, hop-like heads after flowering make it a fascinating little plant to get to know.
• Part of the characteristic flora of dry, unfertilised grassland and dykes.

Hop trefoil: where does it grow best?

• In the wild in dry grassland, poor verges, dunes, on dykes, railway banks, sandy field edges and in poor lawns.
• Full sun.
• Dry to fairly dry, poor soil: sand, gravel or limy soil; no heavy, wet clay.
• In the garden: in a poor flowering lawn, a sand or gravel garden or a sunny bank that you rarely mow.

Goes well with

• Lesser trefoil: Another small yellow clover in the same poor lawn.
• Common bird’s-foot trefoil: Larger yellow flowers and food plant of the common blue.
• Oxeye daisy: White flowers in a dry wildflower meadow.
• Salad burnet: Fine leaves and red pompons on limy soil.
• Mouse-ear hawkweed: Low, pale yellow flower heads in a poor lawn.

Hop trefoil: when and how to plant it?

1. Buy seed of native origin from a supplier of native plants, on its own or in a mix for poor wildflower meadows.
2. Sow in September–October or March–April where it is to grow, on open, poor soil.
3. Sow thinly, press the seed in and barely cover it.
4. Keep the soil moist until germination.
5. In an existing lawn: rake open a few bare patches and sow there.
6. Never dig up plants in the wild.

Care

Water

Not needed.

Feeding

Do not: with fertiliser the grass wins and the clover disappears.

Mowing

Do not mow a poor lawn or verge too short, at 6–8 cm, and in summer let it flower and set seed for a few weeks before mowing again.

Letting it seed

As an annual it must set seed every year. Mow only once the brown heads are dry.

Open patches

A few bare patches in the turf help the seed germinate.

Tip: If you want hop trefoil in your lawn, stop mowing for a few weeks in June and July: that way it can flower and set seed, and it will come back the next year.

Pruning and mowing

Pruning months: July and September.

When: No real pruning. Mow a dry verge or wildflower meadow in July, after the first seed set, and again in September.

How:

• Mow only when most of the heads are brown and dry, so the seed can fall.
• Leave the cuttings for a few days so the last seeds drop out, then remove them.
• In a lawn: set the mower high and skip a few cuts in summer.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Seed

Ripens from June to September. Pick dry, brown heads, rub them out and sow straight away or in spring.

Hop trefoil: how does it get through the winter?

Hardy to −20 °C.

• It dies after setting seed; autumn seedlings overwinter as small rosettes.
• The seed overwinters in the soil.
• The small rosettes stand up well to frost, but not to soil that stays wet for long.

Diseases and pests

• Competition: It disappears in rich, dense grass. Mow, remove the cuttings and do not fertilise.
• Mowing too short: If a lawn is cut short every week, it hardly sets seed. Mow higher or less often.
• Drought at germination: It germinates poorly in a dry spring. Preferably sow in autumn.
• Slugs: In a wet spring slugs sometimes eat the seedlings. Sow a little more thickly.

Through the year

• March: Sow on bare patches; autumn seedlings grow.
• May: First yellow heads.
• June: Full flower; bees and bumblebees on the lawn.
• July: The first heads turn brown like little hop cones. Mow after seed set.
• August: Flowers on the regrowth; seed ripens.
• September: Second cut; sowing possible.
• October: Autumn seedlings appear.

Did you know?

• The name hop trefoil refers to the faded heads, which look like small hop cones.
• Campestre means ‘of the fields’.
• It is one of three common small yellow clovers, together with lesser trefoil and black medick; black medick is not a true clover at all, but a medick, like lucerne.