Why Is My Radish Bolting and Going to Flower?

Radish that produces a tall flower stalk before forming a proper root, or sends up a flower stalk from a barely-formed root, has bolted. Bolting means the plant has transitioned from its vegetative (root-forming) phase directly to its reproductive (flowering and seeding) phase, bypassing the edible harvest stage. The root becomes woody, hot and inedible as the plant diverts energy into the flower stalk and seed production.

Day length is the main trigger

Most radish varieties are long-day sensitive — they begin flowering when day length exceeds a certain threshold. In the UK and northern Europe, this is typically around late spring and early summer when days lengthen beyond fourteen to sixteen hours. Radish sown in March germinates and begins root development while days are still short, and can be harvested before the long-day trigger kicks in. Radish sown in late May or June often starts bolting before the root has developed because the long days trigger flowering almost immediately. Sow early in spring (March–April) and again in late summer (August–September) to avoid the long-day window.

Heat accelerates bolting

High temperatures work with long days to accelerate bolting. A heat wave in June can cause even a recently sown radish to bolt within days. Summer sowings of standard round radish types rarely produce usable roots in hot climates. Use daikon or mooli varieties for summer growing — they are specifically bred to tolerate long days and high temperatures without bolting immediately.

What to do with bolted plants

A radish that has bolted and sent up a flower stalk will not produce a usable root — remove the plant. However, the young seed pods that form after the flowers are edible and have a pleasant peppery flavour — a bonus crop from a plant you would otherwise have discarded. Allow the pods to reach full size but harvest before they dry and split.

Variety choice for bolt resistance

Some varieties have been specifically bred for slow bolting. Check seed catalogue descriptions for "slow to bolt," "summer radish" or "bolt-resistant" and select appropriate varieties for each season's sowing.