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1 October 2020

How to grow runner beans

Find out how to grow delicious-tasting beans, including how to avoid summer gluts
Runner beans

Avoiding gluts of beans

Beans produce plentiful crops so to avoid being overwhelmed, the trick is to grow just the right amount of plants for your needs. In the Which? Gardening trial, most varieties produced at least 0.5kg per plant, and our Best Buy runner-bean varieties produced up to 1kg per plant in a season. So a single wigwam of a dozen plants would be plenty for a small household.

No need for a bean trench

Runner beans produce better crops in a moisture-retentive soil. However there's no need to dig an old-fashioned bean trench as just digging in or mulching with organic matter, such as garden compost or soil improver, will help.

Create a support

Use bamboo canes, at least 2.4m tall, pushed well into the ground. You'll see all kinds of imaginative structures on allotments, but when Which? Gardening trialled bean supports, we found that the best three methods were: wigwam, X-frame, and A-frame. 

A wigwam is quick and easy to put up. It also has a neat, compact shape that takes up little space. 

An X-frame is created with pairs of bamboo canes inserted at 45 degrees to the ground, crossing halfway up and tied in the middle. These are strengthened by a horizontal pole tied where the canes cross. The beans are easy to pick as they hang on the outer edge of the support. 

An A-frame is very robust, easy to erect and dismantle, and good at suppressing weeds.

Getting the earliest runner beans

In the Which? Gardening trial, we shaved around a month off our time for the first harvest, starting picking in the first week of July. To do this, in late March we pre-germinated seeds by putting them on damp kitchen paper until they grow a root around 2-3mm long. We then sowed them in pots and kept them in a coldframe before planting outside in early May when they were only about 15cm tall as we found that smaller plants are less prone to cold damage, and so the plants can establish and grow on more rapidly. We covered the plants with fleece if frost threatened.

Getting the highest yield of runner beans

In the Which? Gardening trial, we got the highest yield from plants sown in the last week of May, both indoors and out. These grew vigorously and cropped from the second to the third week of August until the first frosts.

How to plant runner beans

Space plants at least 15cm apart, in single rows, double rows that are 60cm apart, or around wigwams. Runner beans are damaged by frost so be sure to harden them off before planting to prepare them for colder temperatures outdoors. To harden off plants grown in the coldframe, keep the lid half-open during the day when sunny for the first six days, fully open during the day when sunny for the next six days, and left open day and night for the last six days. Doing it like this will result in tougher plants.

Watering your plants

Once they get going, runner beans need little attention, apart from regular watering in dry summers. Give a good soaking weekly, rather than a light sprinkle every day. 

Picking your beans

The main job is keeping up with picking beans. Do this at least twice weekly. If threatened with a glut, put the bigger ones on the compost heap and pick the pods that are smaller as they'll be more tender for eating.

Runner-bean troubleshooter

  • Blackfly is the most common pest. Either squash these insects or spray them with an organic insecticide.
  • Halo blight is a seed-borne disease that produces circular lesions and can cause the leaves to drop. There's no destroy so destroy any affected plants.
  • Sometimes plants flower but don't produce beans. There are several possible causes, including dry roots and cold nights. Usually cropping picks up as conditions improve. Runner-bean varieties that have been crossed with French beans are less prone to this problem, such as 'Moonlight'.

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