Trifolium subterraneum aka Sub Clover

Trifolium subterraneum is also known as subterranean clover. It is an annual in Fabaceae, the pea family. Its life cycle takes no more than one year. Its native range spans Europe to the Caucasus, and Macaronesia to Iran. Britain and Ireland also lie within its native range. This small plant grows about 0.7 feet [0.2 metres] high. It grows in regions with a temperate climate.

Wild plants grow in pastures with sand or gravel. They also grow on cliff tops. These sites have open ground, not deep shade. Each flower has both male and female organs. Insects move pollen between the flowers. Once the flowers fade, the fruiting head pushes into the soil. This puts the seed below ground and gives the plant its common name. The supplied sources give no more facts about this species' leaves or flower colour.

Choose a sunny site where moist soil drains well. This plant will not grow in shade. It grows in sand, loam and clay, even with few nutrients. Soil near neutral suits it best. It also grows in slightly acid or slightly alkaline soil. Yet the habitat account says wild plants avoid acid ground. PFAF lists USDA zones 7–10 but says winter survival is limited. Soak seed in warm water for 12 hours. Then sow it in place in spring.

Subterranean clover serves as green manure and ground cover. Soil bacteria form nodules, or small lumps, on its roots. They fix nitrogen, and the plant uses some for growth. PFAF suggests sowing clover beneath greenhouse tomatoes before planting the crop. It also suggests growing clover beneath soft fruit. There, cut the clover once or twice in summer. PFAF also suggests growing it in an apple orchard. It reports gains in apple flavour and storage. But it gives no trial details to back that claim.

Do not plant it beside gooseberries or camellias. It can shelter a mite that harms both plants. The mite can cause gooseberries to drop their fruit. It can also make camellias form buds too soon. PFAF lists the leaves as edible, raw or cooked. It gives the plant a low food-use rating. PFAF reports no known hazards and no known medicinal uses. That does not mean the plant is safe for pets. PFAF does not flag this species as weedy.