Subterranean Clover

Subterranean clover (Trifolium subterraneum) is a low-growing annual legume native to Europe, Southwest Asia, and Northwest Africa, distinguished by its unique geocarpic seed development — after flowering, the plant buries its own seed heads underground for protection and germination. It is widely used as a green manure and cover crop, fixing atmospheric nitrogen and suppressing weeds. Its creeping stems spread across the soil surface, forming a dense, weed-suppressing mat. It performs best in cool, moist conditions and tolerates light frosts.

Growing

Sow seeds directly into prepared soil once the soil temperature reaches at least 5 °C. Broadcast or drill seeds at a depth of 1 cm, raking lightly to cover. Aim for a spacing of approximately 15 cm between plants when drilling in rows, or sow at 2–5 g per square metre when broadcasting as a cover crop. No indoor starting is needed. Firm the seedbed after sowing to ensure good soil contact, which aids the characteristic underground seed burial later in the cycle.

Care

Once established, subterranean clover requires little intervention. Water during prolonged dry spells to maintain even soil moisture, but avoid waterlogging. No supplementary feeding is needed — as a nitrogen-fixing legume, it enriches the soil. If used as green manure, cut or dig the crop into the soil when it reaches full flower but before seeds set; this maximises the nitrogen benefit. Avoid heavy foot traffic, which can disrupt the developing geocarpic seed heads.

Harvest

For green manure use, incorporate the entire plant into the soil when it is in full flower and the biomass is at its peak. For seed saving, allow the plant to complete its natural cycle: it will bury its own seed heads into the soil surface. Collect buried seed clusters once the stems have dried and the seeds feel firm and hard. The harvest window is approximately 30 days from peak flowering to seed maturity.

In the kitchen

Subterranean clover is grown primarily as a green manure and cover crop rather than for culinary use. The young shoots and leaves are edible and can be used raw in salads or lightly cooked, similarly to other clovers, but it is rarely grown for the table. Its primary value in the kitchen garden is indirect — it enriches the soil for subsequent food crops.

Storing

Seeds collected for re-sowing should be dried thoroughly at room temperature, then stored in a paper envelope or sealed container in a cool, dry, dark place. Under these conditions, viability remains good for 2–3 years. Green manure material is incorporated directly into the soil and not stored.