Radishes are the fastest vegetable in the garden; the spring types are ready in 20 to 30 days. Radiant is a mix of round and oblong roots in red, pink, purple and white, so a single row gives a varied bunch. Sow it every week or two from the time the soil can be worked, about six weeks before last frost, through late spring, then again in late summer for a fall crop.
Never transplant. Direct sow a half inch deep in loose, fine soil with the stones raked out, and thin to 2 to 3 inches as soon as the seedlings are up; crowded radishes make leaves, not roots. Keep the soil evenly moist, since dry spells followed by water split the roots, and pull them as soon as they size up. A radish left in the ground a week too long turns woody and hot.
Spring radishes bolt in summer heat, so stop sowing when days pass 80°F and resume when they cool. Flea beetles pit the leaves but rarely matter to the root; a row cover at sowing keeps them off. The pods of a plant allowed to flower are edible and crunchy, and the flowers feed small bees.
Clubroot
Swollen, distorted roots; wilting in midday heat; stunted growth and yellowing foliage. Plants recover poorly even with watering.
Remove and destroy infected plants with roots. Raise soil pH toward 7.2 with lime. Improve drainage and rotate out of brassicas for several years.
White Rust
Raised white to cream-colored pustules on leaf undersides, with yellow blotches on upper surfaces. Infected tissue may swell or distort.
Remove and destroy infected leaves. Improve air circulation and avoid overhead watering. Rotate brassicas and avoid planting in previously infected soil.
Damping Off
Seedlings collapse at the soil line with thin, water-soaked stems; seeds may fail to emerge or rot before sprouting.
Sow in well-draining mix, avoid overwatering, and ensure good airflow. Remove affected seedlings and let the surface dry between waterings.
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.
Alternaria blight
Brown circular spots with yellow halos on leaves; spreads rapidly in wet weather.
Remove affected leaves immediately. Water at the base only. A copper-based fungicide can help if caught early.
Flea Beetle
Alticini →Small round shot-holes scattered across leaves; tiny dark beetles that jump when disturbed. Heavy feeding stunts young plants.
Use floating row covers on seedlings. Remove crop debris and weeds that harbor beetles. Apply kaolin clay or spinosad if damage is severe.
Aphids
Aphididae →Clusters of small soft insects on new growth and flower buds.
Knock off with a strong jet of water. Ladybirds and lacewings are natural predators. Insecticidal soap as last resort.