Lesser trefoil

How to recognise it

Habit

Slender, branched annual, 5–30 cm, sprawling or ascending, hairless or slightly hairy.

Leaf

Trifoliate; the leaflets are obovate, 5–10 mm, slightly toothed or notched at the tip. The middle leaflet sits on a short stalk, the side leaflets are stalkless.

Flower

Small yellow heads of 5–9 mm with 3–15 flowers, on a thin stalk from the leaf axil. Flowers from May to September.

Fruit/Seed

After flowering the flowers turn brown and stay wrapped around the small one-seeded pod.

Roots

A thin taproot with nitrogen-fixing nodules.

Confusion with

Hop trefoil has larger heads with 20–40 flowers and a furrowed standard. Black medick has a tiny point at the tip of the leaflets and black, kidney-shaped pods. Slender trefoil is even finer, with 2–6 flowers per head on hair-thin stalks.

Flowering: May–September · Pruning: July and September

Why grow it?

• Flowers for months, from May to September, even in a lawn you do not cut too short: small bees and bumblebees collect nectar from it.
• One of the small clovers that turn an ordinary lawn into a flowery bee lawn.
• As a member of the pea family it fixes nitrogen through nodules on its roots.
• Seedlings quickly fill bare patches in lawns and verges.
• A plant with a story: in Ireland it is often named as the shamrock of Saint Patrick.

Lesser trefoil: where does it grow best?

• In the wild in grassland, lawns, verges, on dykes, field edges, railway land, in dunes and between paving stones.
• Sun; it tolerates light shade.
• Dry to moist, moderately rich soil: sand, loam or light clay.
• In the garden: in a flowery lawn, a dry wildflower meadow, between paving or in a gravel garden.

Goes well with

• White clover: White pompons and creeping stems in the same bee lawn.
• Daisy: Flowers almost all year round in the same lawn.
• Common bird’s-foot trefoil: Larger yellow flowers for bumblebees.
• Selfheal: Purple spikes in a lawn you do not cut too short.
• Mouse-ear hawkweed: Pale yellow flower heads on the driest spots of the lawn.

Lesser trefoil: when and how to plant it?

1. Lesser trefoil usually turns up by itself in a lawn that you do not feed and do not cut too short.
2. If you want to sow it, buy seed of native origin and sow in September–October or March–April.
3. Rake open bare patches in the lawn, scatter the seed thinly and firm it with your foot or a board.
4. Keep the soil moist until germination.
5. Do not mow over the seedlings for the first few weeks.
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 cut too short, at 5–8 cm, and skip a cut now and then while it flowers, so it can set seed.

Letting it seed

As an annual it needs to set seed every year. Leave a strip unmown in summer.

Bare patches

A lawn with a little open soil here and there gives more clover.

Tip: Leave a strip of your lawn unmown for a few weeks in June: lesser trefoil then sets seed and you will have more small yellow flowers for the bees every year.

Pruning and mowing

Pruning months: July and September.

When: No real pruning. Mow a wildflower meadow in July and September; mow a lawn as usual, but not too short.

How:

• Mow a flowery lawn every two to three weeks at 5–8 cm.
• In June, leave a strip uncut for a few weeks so the heads can ripen.
• Mow a wildflower meadow in July and in September and remove the cuttings.

Pruning: when and how · Pruning calendar and basic rules

Propagation

Seed

Ripens from June. It self-sows; if you want to collect seed, pick dry, brown heads and rub them out.

Lesser trefoil: how does it get through the winter?

Hardy to −20 °C.

• It dies after setting seed; autumn seedlings overwinter as small plants among the grass.
• The seed overwinters in the soil.
• The young plants stand up well to frost.

Diseases and pests

• Disappearing: It disappears in a fed, dense lawn. Stop feeding and remove the clippings.
• Mowing too short: With a short cut every week it hardly sets seed. Mow higher or less often.
• Drought: In a dry summer the plants wither early; the seed in the soil produces a new generation.
• Confusion: The small yellow clovers look alike. Count the flowers per head and look at the stalk of the middle leaflet.

Through the year

• March: Rake open bare patches in the lawn and sow.
• April: Seedlings and overwintered plants grow among the grass.
• May: First yellow heads.
• June: Full flower; leave a strip of lawn unmown.
• July: Heads turn brown; mow the wildflower meadow after seed set.
• August: Still flowering; do not mow too short.
• September: Second cut of the wildflower meadow. Sowing possible.
• October: Autumn seedlings appear among the grass.

Did you know?

• Dubium means ‘doubtful’: the species is hard to tell apart from other small yellow clovers.
• When people in Ireland were asked, in the late 19th century and again in the 1980s, to send in a true shamrock, lesser trefoil was the species sent most often.
• Unlike white clover, which persists with creeping stems, lesser trefoil is an annual and has to come up from seed again every year.