Why Have My Beans Stopped Producing in Hot Weather?

A bean plant that was producing well and then abruptly stops flowering or setting new pods during a summer heatwave is experiencing heat stress. Beans — particularly runner beans — have a narrow temperature window for successful pollen production and pod set, and sustained temperatures above 25°C cause pollen sterility, flower abortion, and a complete temporary halt to pod production. The plant does not die, it does not lose its leaves, and it will resume production when temperatures moderate — but during the heatwave, no amount of watering or feeding will force pod set in the heat-affected window.

What is actually happening at high temperatures

At temperatures above 25°C, particularly when night temperatures stay above 18°C, bean pollen becomes non-viable — the pollen grains either fail to develop properly or lose viability before they can fertilise flowers. Flowers are formed and open but cannot set pods because fertilisation fails. The plant then drops the flowers rather than attempting to develop empty pods. This is a physiological response to heat that is hardwired into the plant's genetics and cannot be overridden by growing conditions.

What to do during a heatwave

Keep watering consistently — even if no new pods are setting, keeping the plant alive and healthy means it will flower again once temperatures moderate. Water deeply at the base in the early morning or evening, never in full midday sun when cold water on hot soil can cause shock. If possible, provide afternoon shade with shade cloth or netting. Misting the foliage in the evening cools the plant slightly and may marginally improve pollen viability. Harvest any existing pods promptly — they continue to develop even in heat.

The second flush

After a heatwave breaks, runner beans typically produce a second wave of flowering and a generous late-season pod set. This second flush, in August or September in a typical UK summer, can be as productive as the first. Plants that survived the heatwave in good condition with healthy foliage and consistent watering produce much better second flushes than those that were allowed to dry out badly or lost significant leaf area to disease.