Tasty and nutritious runner beans also add goodness to the soil and look stunning. Writing in his ‘Herbal’ four centuries ago, the botanist Gerard says the flowers of runner beans, Phaseolus coccineus, “are large, and of an elegant scarlet colour, whence it is vulgarly termed by our florists, the Scarlet Bean.” These runner beans are now available in individual or bi-coloured whites, red and pinks.

When first introduced to Europe from Central America in the 16th Century, these ‘scarlet’ flowers, not the beans, were what the runners were all about. Our early plants were tiny compared to their Central American relatives, which could nimbly climb to 6 metres.

Without killing winter frosts, perennial Central American runners do grow much more strongly than European introductions initially did because they already had a close symbiotic partnership with specialist rhizobial bacteria that weren’t present in European soils. Rhizobia form partnerships with particular families and species, such as peas or broad beans, so each has a limited choice of partner rhizobia.

It’s not known how runner bean rhizobia reached Europe, but interestingly, they were first identified in Spain and Austria, the territory ruled by the Hapsburgs, the royal dynasty that first laid claim to 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 making it available to the plant in a form that can be used for its growth.

Even when a plant dies, the nodules retain this nitrogen which is gradually released into surrounding soil. So, when clearing a patch, cut the stem at ground level and leave the roots in the soil.

Do this too with broad beans, which form a symbiotic relationship with different bacteria. If you decide to dig or pull the whole plant up, the nitrogen will be released into the compost bin rather than an individual bed. Under no circumstances should you bin or discard these valuable plant vines!

As we all know, runner beans grow vigorously and crop profusely provided they survive the initial onslaught of slugs and will scale any pole widdershins [anti-clockwise]. Though not reaching 6m, they always manage to outgrow my bean frame and throw out a dense cluster of sideshoots in the middle of the frame. And nipping out growing points merely stimulates a bigger forest of lower shoots.

The gardener’s challenge is keeping pace with the crop. Obviously small pods are tastiest but you keep coming across large ones lurking in the middle. It seems crazy to guiltily eat the big stringy fellas and leave sweet, tender ones the chance to become unpalatable.

This hair shirt approach is utterly pointless. Why not select choice ones and leave the rest to grow on? It’s true that a plant developing its own seed will stop producing pods, or at least slow down the process. To prevent this, simply pick and compost the overly large pods or give them to the poultry if, like me, you have any.

But I’m not sure how long you’d want to prolong the harvest. After late September beans gradually become pretty tasteless as the sun weakens, so are they really worth picking?

Alternatively, leave the beans that got away to form seed and then harvest them, as you would broad beans. They freeze well and can be added to stews over the winter.

Admittedly they’re more fiddly to pod, but I reckon it’s a job worth doing.

You could also let beans ripen and save as seed for next year, provided you’ve been growing an open-pollinated, not F1 variety. Or grow fewer plants next year.

Plant of the week

Foxglove, Digitalis purpurea f. albiflora, white flowered, it is a naturally occurring form of the more common purple foxglove. The white one is equally attractive to bumblebees and looks stunning grown in numbers through a semi shaded border.