Why are my runner beans tough and stringy?

The string in a runner bean is a fibre that develops along the seam as the pod matures towards seed production. It is a function of age, not of watering or feeding, so the answer is almost entirely about how often you go down the row.

Step by step

1. Pick at 15–20cm, flat and pliable.The pod should snap cleanly when bent, with a crisp break and no fibres bridging the gap. If it bends without snapping, it has gone.
2. Look at the pod against the light.If you can see the outline of swelling beans through the wall, the string is already forming. Pick it now and use it, or leave it entirely and let it dry for seed.
3. Go down the row every two or three days in peak season.In warm weather a bean goes from perfect to stringy in about four days. Weekly picking is why most people's beans are tough.
4. Strip every mature pod off, even ones you do not want.A single pod left to mature tells the plant to stop flowering. Clearing the row keeps it cropping for another month or more.
5. Grow a stringless variety if you cannot pick often.Modern stringless runner varieties hold quality noticeably longer, which matters if you are only in the garden at weekends. They are usually described as stringless or smooth-podded on the packet.
6. Keep the row watered.Water stress will not create string on its own, but it makes pods tougher and more fibrous and it slows growth so pods sit at the wrong size longer.
7. Deal with the ones that got away.Slice them very thinly across the pod on a bean slicer or with a knife, which cuts the string into short pieces. Very old pods are better shelled — the beans inside are good eating, fresh or dried.

Tips

• A bean slicer costs very little and turns marginal pods into perfectly good food. It is worth having if you grow a full row.
• Freeze a glut rather than letting pods stand on the plant — blanch briefly, cool and bag. Beans left to hold on the plant stop the crop.
• Old varieties often have the best flavour but the worst string. Growing one row of a traditional variety and one of a stringless one is a good compromise.
• Runner bean seeds from a mature pod are perfectly edible fresh, shelled and boiled like a broad bean, and can be dried for storage.

Common mistakes

• Picking once a week — The window between a tender pod and a stringy one is only a few days in warm weather. Frequency is the whole answer.
• Leaving small pods to 'get bigger' — They get longer and tougher at the same time. Length is not the same as yield — picking small and often gives you more total crop, because the plant keeps flowering.
• Blaming the soil or the feeding — String is developmental. No feed, mulch or watering regime prevents a pod that has been left on the plant too long from being stringy.

Questions people ask