Why vegetables bolt and go to seed

First check: identify the crop and distinguish normal flowering from flowering before the part you want to harvest has developed. Bolting is premature movement into flowering and seed production, often reducing the useful harvest.

It is not always caused by heat

Different crops respond to different signals. Increasing day length encourages flowering in some annual vegetables, including spinach and some lettuces. Stress can bring forward the loss of harvest quality.

Some biennials, such as onions, carrots and beetroot, can be prompted towards flowering after cold exposure. The trigger may happen well before a flower stalk becomes visible. Moving a bolting plant somewhere cooler therefore does not necessarily reverse the process.

Heat and dry conditions also matter for many leafy crops. With kohlrabi, both early cold and hot, dry growth can cause difficulties. Check that crop's requirements rather than applying one rule to every vegetable.

What to do with an affected crop

Harvest usable produce promptly if quality is still acceptable. Once flowering is established, cutting off the stalk will not reliably restore the intended leafy, root or bulb crop. Avoid repeatedly feeding a plant in an attempt to turn it back into a younger one.

If space allows, a few healthy flowering plants can be left for insects or seed, where appropriate. Keep them separate from the harvest plan and remember that saved seed may cross with related plants or fail to reproduce an F1 variety faithfully.

Reduce losses in the next sowing

Choose a variety suited to the season, including bolt-resistant types where available. Resistance lowers risk; it is not a guarantee in unsuitable conditions. For onions prone to bolting, heat-treated sets can be worth considering.

Use the crop's recommended local sowing window. Do not copy calendar dates from a different climate without checking them. Protect susceptible young plants from inappropriate cold exposure, harden off transplants and avoid leaving them cramped or repeatedly wilted in small modules.

Maintain suitable moisture and sow small successive batches instead of relying on one large planting. If midsummer repeatedly defeats a cool-season crop, a spring or late-summer sowing may fit your conditions better.

Make timing easier to review

Record varieties and sowing dates in Your Growing Companion. Its sowing calendar and cold alerts can support planning; they do not measure day length responses or guarantee that a crop will avoid bolting.

Back to Solve a Growing Problem · Find your crop guide

Further reading: RHS guidance on bolting, successional sowing, transplanting and kohlrabi problems.

By Simon Adams · Published 27 October 2026. Adapt advice to your crop and conditions.