Delicious and nutritious runner beans also add goodness to the soil and look stunning. In his ‘Herbal’ the botanist Gerard wrote four centuries ago that the flowers of the runner beans, Phaseolus coccineus, “are large and have an elegant scarlet color, which is why it is vulgarly referred to by our florists as the scarlet bean”. These runner beans are now available in single or two-tone shades of white, red and pink.
When it was first introduced to Europe from Central America in the 16th century, those “scarlet” flowers, not the beans, were what runners were about. Our early plants were tiny compared to their Central American relatives, which could nimbly climb 6 meters.
Without killing winter frosts, perennial Central American runners grow much more strongly than originally European introductions, as they already had a close symbiotic partnership with special rhizobial bacteria that were not present in European soils. Rhizobia form partnerships with specific families and species, such as peas or broad beans, so that each has a limited range of partner rhizobia.
It is not known how runner bean rhizobia got to Europe, but interestingly, they were first identified in Spain and Austria, the area ruled by the Habsburgs, the royal dynasty that first claimed much of the New World.
Legumes use tiny hairs on their roots to develop nodules in which the rhizobia live. They fix nitrogen gas from air pockets in the soil and make it available to the plant in a form that can be used for its growth.
Even when a plant dies, the tubers retain this nitrogen, which is gradually released into the surrounding soil. So when clearing a bed, cut the stem near the ground and leave the roots in the ground.
Do the same with broad beans, which form a symbiosis with various bacteria. If you decide to dig up or pull out the whole plant, the nitrogen will be released into the compost bin rather than a single bed. Under no circumstances should you dispose of or throw away these valuable plant vines!
As we all know, pole beans will grow vigorously and flourish abundantly provided they survive the initial onslaught of snails and will overcome any pole rams [anti-clockwise]. Although they don’t reach 6m, they always manage to grow out of my bean frame and throw a dense cluster of side shoots in the center of the frame. And pinching out growth points only stimulates a larger forest of lower shoots.
The gardener’s challenge is keeping up with the harvest. Of course, small pods are the most delicious, but you always come across large ones lurking in the middle. It seems insane to guiltily eat the big, wiry guys and leave sweet, tender ones a chance to become inedible.
This hair shirt approach is completely pointless. Why not choose selected ones and let the rest grow? It is true that a plant that develops its own seed will stop producing pods, or at least slow down the process. To prevent this from happening, just pick and compost the oversized pods or give them to the poultry if you, like me, have some.
But I am not sure how long you would like to extend the harvest. From the end of September, as the sun fades, the beans start to get pretty tasteless, so is it really worth picking?
Alternatively, leave the beans that escaped to form seeds, and then harvest them like you would with broad beans. They freeze well and can be added to stews over the winter.
Granted, they are fiddier, but I think it’s a job well worth it.
You can also let the beans ripen and keep them as seeds for the next year, provided you’ve grown an openly pollinated variety, not an F1 variety. Or grow fewer plants next year.
Plant of the week
Foxglove, Digitalis purpurea f. Albiflora, white-flowered, is a naturally occurring form of the more common purple foxglove. The white one is equally attractive to bumblebees and looks stunning when grown in number thanks to a partially shaded border.
