Why are my runner beans flowering but not setting pods?

Runner beans are the crop most likely to produce a magnificent wall of flowers and no beans at all. Unlike French beans, which are largely self-fertile, runners depend on insects to move pollen between flowers, and they abort flowers readily when the soil dries. In a hot dry British summer both conditions can fail at once.

Step by step

1. Water the roots hard and often once flowering starts.This is the fix that works most often. Runner beans are thirsty and shallow-rooted, and dry soil at flowering aborts flowers within days. A thorough soak twice a week in dry weather beats a daily sprinkle.
2. Mulch the base of the row generously.Compost, grass clippings or straw over damp soil keeps the root zone even. A row that swings between wet and dry sets badly however much you water in total.
3. Check whether insects are actually visiting.Stand by the row for two minutes on a warm morning. If nothing is working the flowers, the problem is pollination — and that is usually a site with no other flowers near it, or a run of cold wet weather grounding the bees.
4. Plant something for pollinators alongside.A short row of annuals near the beans — poached egg plant, borage, marigolds, sweet peas up the same canes — reliably brings insects into the area. It is the single cheapest fix for a bee-poor garden.
5. Consider night temperature.Runner beans set poorly when nights stay above roughly 16°C, which is why a heatwave produces flower after flower and no pods. Nothing fixes it but cooler weather; the plants usually set heavily as soon as it breaks.
6. Rule out a nitrogen-rich site.Beans fix their own nitrogen. Planted into ground heavily fed with a general fertiliser they make enormous foliage and few pods. Feed the ground with organic matter and potash rather than nitrogen.
7. Look for damage at the base of the flowers.Small holes bitten in the back of the flower are bumblebees robbing nectar without pollinating. It is common and there is nothing to be done, but it explains flowers that are visited and still fail.
8. Keep picking whatever does set.One mature pod left on the plant signals that the job is done and slows flowering. Picking every two or three days keeps the plant producing right through to the frosts.

Tips

• Spraying the flowers with water is a very old piece of advice and does very little. Water the roots instead — that is where the effect is.
• If you get poor set every year, grow climbing French beans alongside. They are self-fertile, set without insects and crop reliably in a hot summer when runners will not.
• Some varieties are bred specifically for reliable setting in poor conditions, including self-fertile runner types — worth seeking out on a difficult site.
• A row that gets shade in the hottest part of the afternoon often sets better in a heatwave than one in full sun all day.

Common mistakes

• Feeding with a nitrogen-rich fertiliser to encourage the plant — Beans already fix nitrogen. Adding more produces lush growth and delays or reduces pod set.
• Letting the row dry out because the plants look healthy — The foliage stays green long after the flowers have started aborting. By the time the plant looks stressed you have lost weeks of setting.
• Planting a single short row in an isolated corner — Fewer flowers in one place attracts fewer pollinators. Beans set better near other flowering plants.

If it doesn't work

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