Why Are My Radish Roots Swollen and Deformed?

Radish roots that pull up as irregular club-shaped swellings, distorted lumpy masses, or a fused tangle rather than a clean round or elongated root may be infected with clubroot — a serious soil-borne disease. Clubroot (Plasmodiophora brassicae) affects the entire brassica family including radish, turnip, broccoli and cabbage. It is one of the most persistent and difficult-to-eliminate soil diseases a vegetable gardener encounters.

How to identify clubroot

Above ground, affected plants wilt in dry weather even when soil moisture appears adequate, and may show yellowing and stunting. Below ground, the taproot and lateral roots are replaced by irregular, swollen, club-shaped galls — often covered with secondary rots that make them smell unpleasant. Young infections may produce small, round galls on lateral roots while the main root looks almost normal. Advanced cases leave virtually no usable root tissue. The disease is confirmed by the characteristic root galls; no other common radish problem produces this symptom.

How clubroot spreads and persists

Clubroot produces resting spores that survive in the soil for fifteen to twenty years. The spores are spread via infected soil on tools, boots, transplants and drainage water. Even a small amount of infested soil moved to a new bed can establish the disease there. Destruction of infected plant material is critical — do not compost clubroot-infected roots; bag and dispose of them in household waste.

Lime to raise pH

Clubroot thrives in acidic soils (pH below 7). Liming to raise the soil pH to 7.0–7.5 significantly reduces the severity of clubroot symptoms — not because it kills the spores but because the organism is less active at higher pH. Apply garden lime (calcium carbonate) or calcium hydroxide to raise the pH before planting. This does not eliminate clubroot but can allow acceptable crops in mildly infected soils.

Resistant varieties and long rotation

A growing number of brassica varieties carry clubroot resistance. For radish, choice is more limited than for broccoli or cabbage, but some suppliers list clubroot-tolerant types. Avoid growing any brassica crop in an affected bed for at least five to seven years; ideally, rotate to non-brassica crops indefinitely in seriously affected beds.