Grower’s Corner – runner beans
Runner beans are incredibly easy to grow, in fact they are the first crop (after radishes and lettuce) that most novice gardeners get involved with. This doesn’t mean there aren’t some tricks to producing the perfect crop though! Originally a perennial plant from South America, they are grown in the UK as a half-hardy annual, being struck down each year by the frost and they are also deep-rooted, requiring a well-drained but moisture-retentive soil to which organic matter has been added the previous autumn. Acid soils may need liming.
You also need to rotate the crop annually to reduce soil pest and disease problems and make sure you don’t sow or plant outside until late May to avoid cold damage (runner beans need a minimum soil temperature of 10ºC/50ºF to germinate). Foliage is dense and so wind damage can occur if the situation is too exposed. A final consideration is that the shade cast by these plants, which can reach six feet tall, will not be a problem to other growing vegetables, or grow the dwarfing varieties which don’t crop so well but won’t interfere with other crops on your site.
When you are planting out your seedlings, you can use cloches or plastic bottles with the bottom cut off placed over the seedlings if an unusually late frost is expected. Runner beans will require support and the traditional form is a wigwam - four or five bamboo canes tied together at the top will be sufficient – smart gardeners will loop some gardening twine round the bamboo canes at about a foot off the ground and again about three feet up, this will give the growing plants more to grab hold of.
The runner bean tends to produce many more flowers than beans for a variety of reasons:
- Watering the soil at the base of the plant has a beneficial effect on flowering and pod setting as does applying a mulch to conserve soil moisture. Syringing flowers with water doesn’t help pod set, but if done in late evening may cool the flowers and too much heat can prevent the flowers setting pods.
- Runner beans need bees to pollinate the flowers. Cold, windy weather deters bees, so position plants in a sheltered site. Runner bean nectar is not very rich in sugars, and bee numbers visiting runner beans often increases after July, when more attractive mid-summer nectar sources, such as brambles, lime trees and clovers, have finished flowering – and consider planting pollinators like sweet peas in with your runner beans for maximum early attractiveness to pollinating insects.
- Short-tongued bumblebees cannot reach nectar from the front of the flower, and so bite a hole in the flower base to gain access. This allows bees to get at the nectar but, because they do not come into contact with the reproductive parts of the flower, does not result in pollination. There is no way to prevent this but sufficient bees usually visit the flowers in the conventional way for a good crop’
- Birds occasionally peck flowers, leaving tattered petals on the plant and surrounding ground. If this is a recurring problem grow dwarf cultivars that can be protected with netting.
Runner bean photographs by Kai Hendry and author’s own, used under a creative commons attribution licence