Red clover is a short-lived perennial legume grown as a cover crop and forage. Its deep taproot opens heavy soil and its root nodules fix nitrogen, so a bed sown with it and turned under before flowering goes into the next crop richer than it was. The pink-purple flower heads stand 1 to 2 feet and are worked hard by bumblebees, whose long tongues reach the nectar that honeybees cannot.
Sow it in early spring or late summer, a quarter inch deep at about a quarter pound per 1,000 square feet, and keep it moist until it is up. It tolerates poor soil and part shade and needs no feeding. As green manure, mow or turn it in when the first flowers show, six to eight weeks before the bed is needed, so it has time to break down. Left to grow, it flowers from late spring into fall and seeds itself.
It is native to Europe and naturalised across North America, where it is common in meadows and lawns. Native clovers are the better choice for a wildflower planting; red clover's place is the vegetable garden, where its roots and flowers do real work between crops.
Powdery mildew
White or grey powdery coating on leaves - usually starting on older growth in humid conditions or when nights cool.
Improve air circulation by thinning plants. Apply neem oil or potassium bicarbonate spray at first sign. Avoid overhead watering.
Downy mildew
Yellowing on top of leaves with grey-purple fuzz underneath. Spreads rapidly in humid conditions.
Remove affected leaves. Improve air circulation. Avoid overhead watering. Copper spray as preventive.
Crown Rot
Lower leaves yellow and wilt; the base of the rosette turns brown and soft, sometimes with white fungal threads at the soil line. Plants collapse in wet conditions.
Remove and destroy affected plants. Improve drainage and avoid overhead watering. Do not mulch directly against the crown. Space plants for airflow and avoid replanting in the same wet spot.
Rust
Orange to brown raised pustules on the undersides of leaves, with yellow spotting on the upper surface. Heavy infections cause leaves to yellow and drop.
Remove and destroy infected leaves. Avoid overhead watering and improve air circulation. Apply a sulfur or copper-based fungicide if it spreads. Clear plant debris in fall.
Southern Anthracnose
Dark sunken lesions on stems and petioles, often girdling and blackening the crown; plants wilt and collapse in patches during warm, wet weather.
Plant resistant varieties, ensure good drainage, and avoid dense overcrowded stands. Remove infected plants and rotate to non-legume cover for a season.