Lotus corniculatus, common bird's-foot trefoil, is one of the most ecologically significant wildflowers in the British Isles: compact, sprawling, brilliantly coloured, and absolutely central to the life cycles of some of the UK's best-loved insects. The plant belongs to the legume family (Fabaceae) and grows as a low-spreading perennial with trifoliate leaves on wiry stems rarely more than 20 to 40 centimetres tall. From May through to September it produces clusters of pea flowers that are genuinely beautiful up close: the standard and wings are bright yellow and the keel is flushed with vivid orange-red, the bicolour combination that gives it the folk name "eggs and bacon." The seed pods that follow ripen into cylindrical brown pods radiating from a central point in exactly the manner of a bird's three front toes and the hind claw, giving the plant its more formal common name.
Bird's-foot trefoil is one of the most widespread grassland wildflowers in the UK, found on chalk downs, limestone grassland, unimproved meadows, road verges, coastal clifftops, and any short, open, nutrient-poor turf in a sunny position. It tolerates exceptionally poor, dry, chalky soil and actually performs better in infertile conditions than in rich garden borders, where vigorous grasses and competitive herbaceous plants crowd it out. It fixes atmospheric nitrogen through symbiotic root nodules, contributing to the soil in the same way as other legumes. The closely related Lotus pedunculatus, greater bird's-foot trefoil, is a taller species with larger flower heads suited to wet grassland and the margins of ponds and ditches. Lotus corniculatus 'Plenus' is a double-flowered ornamental cultivar with fully developed petals that is sometimes offered in nurseries, though it produces no usable pollen or nectar and has no wildlife value.
The ecological importance of Lotus corniculatus is difficult to overstate. It is the primary larval food plant of the common blue butterfly (Polyommatus icarus), one of the most familiar and best-loved British butterflies, and the principal food plant of the six-spot burnet moth (Zygaena filipendulae), the striking red-spotted day-flying moth of chalk grassland and clifftops. A significant number of other moth species also use it as a larval food plant, among them the grass eggar, the narrow-bordered five-spot burnet, and the brown-tail. Understanding this food plant status shapes how you should respond to any problem that affects the plant, including leaf curl.
Aphids
Aphids are the most common cause of leaf curling on Lotus corniculatus and the first thing to check when the small trifoliate leaves at the shoot tips begin curling downward in spring and early summer. Two species in particular are strongly associated with the plant: the clover aphid (Nearctaphis bakeri) and the pea aphid (Acyrthosiphon pisum), a larger, pale green species that is one of the most widespread legume pests in the UK. Both establish colonies on the undersides of the youngest leaflets and on the tender growing tips of the sprawling stems, and both cause the characteristic downward curl of the leaf as they feed on the plant sap.
On a low-growing plant like bird's-foot trefoil, aphid colonies are relatively easy to spot once you are looking for them. Part the foliage at the growing tips of the stems and look at the undersides of the youngest leaves: a colony will appear as a cluster of soft-bodied, green or whitish insects, sometimes with a few winged individuals among them. Sticky honeydew deposits on the leaf surfaces below the feeding sites, which may develop a black coating of sooty mould in warm weather, are another indicator that aphids are active. On young transplants with few stems, a heavy early-season colony can distort the growing tips significantly and slow establishment.
The most important consideration when treating aphids on Lotus corniculatus is the food plant relationship with butterflies and moths. The common blue butterfly and the six-spot burnet moth lay their eggs on the plant, and the caterpillars feed on the leaves. Any insecticide applied to the foliage will kill or harm caterpillars as readily as aphids. Contact insecticides, systemic products, and even "organic" formulations including pyrethrin-based sprays should not be used on or near bird's-foot trefoil at any point during the growing season. The only targeted intervention that does not risk harming the caterpillars or adult insects visiting the plant is a strong jet of water directed at the affected shoot tips, which dislodges the aphids physically. Use this on young transplants where the colony is heavy and the plant small enough to be genuinely damaged. On established plants in a wildflower lawn or meadow, aphid colonies on bird's-foot trefoil are effectively self-limiting: parasitic wasps, ladybird larvae, hoverfly larvae, and lacewing larvae find the colonies and reduce them without any intervention needed. The natural predator community in a garden that avoids insecticides is, in most seasons, fully adequate to prevent lasting damage.
Waterlogging
Waterlogging is the most serious environmental cause of leaf curl and plant decline in Lotus corniculatus, and it is fundamentally a question of placing the right plant in the right site. Bird's-foot trefoil is a dry grassland plant. Its natural habitats are chalk downs, limestone grassland, sandy clifftops, and short, freely-draining turf where winter waterlogging never occurs. In garden soil that remains saturated for extended periods, particularly in the heavy clay soils common across much of lowland England, the root system deteriorates through root rot, and the plant responds with a sequence of symptoms: the trifoliate leaves lose their colour, turning yellowed or pale; the stems begin to wilt even when the soil is wet; and the leaves curl as water uptake from the rotting root system becomes inadequate to maintain turgidity. The decline can set in suddenly after a wet winter and the plant may appear dead before the spring growth would normally resume.
The practical response is straightforward: plant Lotus corniculatus only in freely-draining soil. In a wildflower meadow or lawn on chalk, limestone, or sandy soil, drainage is usually adequate without any modification. On clay or in low-lying areas where water sits after rain, the plant is not suitable and will not thrive regardless of other care. In those conditions, Lotus pedunculatus, the greater bird's-foot trefoil, is the correct species: it is naturally adapted to wet grassland and the edges of ditches, and it provides similar wildlife value in those habitats. Attempting to amend heavy clay with grit to grow Lotus corniculatus is possible in a raised bed or a well-prepared border, but in a large area of lawn or meadow, choosing the right species for the conditions is more practical and more reliable.
Other causes of curling leaves
Powdery mildew (Erysiphe trifolii) affects bird's-foot trefoil, as it does most members of the Fabaceae, producing a white floury coating on the surfaces of the leaflets and causing the leaf margins to curl upward. On Lotus corniculatus, powdery mildew tends to appear in warm, dry conditions from midsummer onwards and is more common on older plants in crowded positions than on young plants or on those growing in open, well-ventilated turf. In a wildflower lawn or meadow where the plant is spreading through short open grass, mildew is rarely a significant problem because the open growing conditions provide natural airflow around the foliage. On plants in a denser border position, improve air circulation by thinning neighbouring vegetation and water during prolonged dry spells to reduce the drought stress that makes the disease worse. On established plants in a good open position, late-season powdery mildew is primarily cosmetic and does not prevent the plant from flowering and seeding successfully.
Drought stress is uncommon on established bird's-foot trefoil, which is genuinely one of the most drought-tolerant wildflowers available for UK planting. Once established in freely-draining soil in an open, sunny position, the plant manages extended dry spells without visible distress, and in its natural chalk grassland habitats it grows on soils with almost no water-retaining capacity. New transplants are more vulnerable: in their first season before the root system has spread, they may wilt and curl the leaflets during prolonged hot, dry weather. Water new transplants through their first summer during dry spells, and they will rapidly become self-sufficient. After the first season, supplementary watering is not necessary and is not beneficial.
Slug and snail damage is worth considering on newly planted specimens or on seedlings. The low-growing habit of Lotus corniculatus places the foliage within easy reach of slugs, and in a typical UK garden, slug populations are high enough to consume young plants at the seedling stage before they become established. Curling and ragged damage on young growth that has no aphids or mildew visible is often slug or snail feeding. Apply a ring of horticultural grit around newly transplanted plugs to deter slugs physically. Once plants have been established for one full season and have developed spreading stems and a more extensive root system, they become substantially less attractive to slugs and the risk diminishes considerably.
Rabbit grazing is relevant in rural gardens and any site adjacent to grassland or hedgerows. Rabbits graze bird's-foot trefoil readily and their feeding, which removes growing tips and young leaves close to the ground, causes irregular curling and distortion of the regrowth as new shoots emerge from the damaged stem ends. Where rabbits are the cause, the feeding is typically on multiple stems simultaneously, often to a uniform height, and may remove all growth above ground level. Protect newly established plants with a low wire guard until the root system is large enough to regenerate after grazing; once well-established, bird's-foot trefoil regrows vigorously from the crown after grazing and is sufficiently persistent to survive in rabbit-grazed areas.
Spider mites can colonise Lotus corniculatus in hot, dry conditions, particularly in enclosed border positions with limited airflow. The characteristic bronzed, stippled appearance on the upper leaf surfaces and fine webbing on the undersides distinguishes mite feeding from other causes. On bird's-foot trefoil growing in an open wildflower lawn or meadow, spider mites are rarely significant because the open conditions and the natural predator community that thrives in unsprayed wildflower planting keeps populations low. In a dry, sheltered border position in a hot summer, check the undersides of affected leaves for mites. A jet of water to the leaf undersides is the safest treatment on a plant with caterpillar food plant value.
Prevention and long-term care
The most effective approach to preventing problems on Lotus corniculatus is to match the plant to the conditions it is naturally suited to. Grow it in full sun in freely-draining, nutrient-poor soil: a chalk or limestone lawn, a sandy wildflower meadow, a dry sunny bank, or a well-drained border where it will not be outcompeted by vigorous neighbours. In these conditions the plant is long-lived, spreading steadily by seed and by the rooting of the spreading stems, and largely free of the problems that affect plants in unsuitable positions.
Avoid insecticides entirely on or near bird's-foot trefoil. This is not a precautionary guideline but a firm requirement for anyone who wants the plant to serve its purpose as a food plant for common blue butterflies and six-spot burnet moths. The caterpillars of these insects are present on the foliage through much of the growing season, and they are killed as readily by most garden insecticides as any target pest. A garden that avoids insecticides entirely will develop a natural predator community that manages aphid outbreaks on bird's-foot trefoil without any human intervention.
Protect young transplants from slugs with a ring of horticultural grit, and avoid planting plug plants or pot-grown specimens into freshly disturbed soil in autumn when slug activity is highest and the plants are smallest. Spring planting into an established lawn or border gives transplants the best chance of growing through the most vulnerable stage during the warmer months when growth is fastest. Once established, bird's-foot trefoil needs no routine care: it flowers prolifically from May to September, fixes its own nitrogen, tolerates drought, and spreads to fill available space. Allow it to self-seed freely. It is one of the most generous and ecologically valuable wildflowers available for UK gardens.
Frequently asked questions
Why are my bird's-foot trefoil leaves curling?
Aphids are the most common cause of bird's-foot trefoil leaves curling, particularly the clover aphid (Nearctaphis bakeri) and the pea aphid (Acyrthosiphon pisum), which colonise the soft shoot tips and cause the small trifoliate leaves to curl downward. Waterlogging in poorly-drained soil causes root rot, yellowing, and leaf curl as the plant deteriorates. Powdery mildew produces a white coating on the leaflets with marginal curl in warm, dry conditions. Drought stress in new transplants, slug and snail feeding on the low-growing foliage, and spider mites in hot, dry summers are less common causes.
Is bird's-foot trefoil a food plant for butterflies and moths?
Yes, Lotus corniculatus is one of the most important food plants for UK butterflies and moths. It is the primary larval food plant of the common blue butterfly (Polyommatus icarus), one of the most widespread and well-loved British butterflies. It is also the principal food plant of the six-spot burnet moth (Zygaena filipendulae), a striking day-flying moth with crimson-spotted black wings. Numerous other moth species use it, including the grass eggar, the narrow-bordered five-spot burnet, and the brown-tail. For this reason, insecticides should never be used on or near bird's-foot trefoil: even treatments aimed at aphids will harm or deter the caterpillars and adult insects that depend on the plant.
Can I grow bird's-foot trefoil in a wildflower lawn?
Yes, Lotus corniculatus is excellent in a wildflower lawn and one of the most rewarding plants to establish in an infrequently mown grass area. It thrives in short, open turf on poor, freely-draining soil, including chalky lawns where little else flourishes. The low-growing, spreading habit and tough stems mean it tolerates occasional mowing well, particularly if the lawn is cut no lower than about 7 to 10 centimetres and mowing is avoided when the plant is flowering from May to September. It spreads readily both by seed and by rooting along the sprawling stems, and in a good position it will colonise a significant area over two or three seasons, bringing brilliant colour and outstanding wildlife value. Avoid applying lawn fertilisers or weedkillers to any area where you want it to establish, as it thrives in poor soil and is killed by most broadleaf herbicides.
What is the difference between Lotus corniculatus and Lotus pedunculatus?
Lotus corniculatus (common bird's-foot trefoil) and Lotus pedunculatus (greater bird's-foot trefoil) are both UK native wildflowers in the legume family, but they suit very different growing conditions. Lotus corniculatus is a plant of dry, freely-draining, nutrient-poor grassland, chalk downs, and sunny road verges: it cannot tolerate waterlogged soil and will deteriorate rapidly in wet conditions. Lotus pedunculatus is taller, reaching 60 centimetres or more, and is the species for wet grassland, boggy meadows, and the edges of ponds and ditches where the soil is consistently moist or seasonally waterlogged. If you have a garden with boggy or heavy clay areas and want a native legume for wildlife, Lotus pedunculatus is the right choice. For a dry, sunny border, a chalk lawn, or a well-drained meadow, Lotus corniculatus is the one to grow.
Why is bird's-foot trefoil called 'eggs and bacon'?
Lotus corniculatus has acquired many folk names over the centuries, and 'eggs and bacon' is among the most widely used in the UK. It refers to the bicolour colouring of the pea flowers: the upper petals are bright yellow, while the keel and the backs of the outer petals are flushed with orange-red, particularly in bud and as the flowers age. The combination of yellow and reddish-orange on the same flower head was fancifully compared to fried eggs and bacon. The name 'bird's-foot trefoil' itself comes from the seed pods, which radiate from a central point in a cluster that resembles the toes and claws of a bird's foot. The plant has many other regional names across the UK, including 'Tom Thumb', 'Granny's toenails', and 'Devil's fingers'.