This guide is specifically about field beans, but I also have guides to growing legumes and spinach alternatives which provide some extra information and context.
Field beans belong to the same family as broad beans, but the pods and beans are smaller. As a result they've traditionally been used as animal feed or as a soil improving green manure over winter.
I'm going to describe a much better use for them, that's proved incredibly popular with my family and friends. Grow them over winter as an amazing spinach alternative, then leave the roots in the ground in spring and harvest and compost the tops. Harvesting before the plants form flowers, maximises the amount of nitrogen they leave in the soil for a follow on crop.
Grown this way you get a great winter and spring harvest and you improve the soil.
I use a rating system to help me decide what to grow and it considers lots of factors, but the main ones are how tasty it is, how healthy it is to eat, how expensive it is to buy, how big it's harvest is, when it's harvest period is and whether I can buy it organically and if not how much it's sprayed.
Field beans score very highly in this system. They are a firm favourite when it comes to taste, with many of my friends and family raving about them as an ingredient in stir-frys, smoothies and even salads. They are healthy too and lower in oxalic acid than spinach. They are impossible to buy in the shops and always will be because they are tricky to harvest at scale.
The harvest is impressive, I generally assume that 1m2 will allow me to harvest about 1 litre a week, for ten weeks, with a total value of about £10. That's not very impressive for a summer crop, but it's excellent in winter and early spring.
Field beans grow almost anywhere, in sun or partial shade, in any time of soil, without any protection over winter and they also do ok in containers, although the yield will be small.
They do best planted at large scale and harvested lightly every week of two and grown in full sun.
The seeds are normally planted direct in the ground and will germinate in about 4 weeks. Once the first shoot has grown to about 4-6 inches above the soil, you will see a tight cluster of leaves, which I describe as a 'growing tip'. Harvest this tip. If you do this first harvest in late October the plant will respond by sending up multiple shoots. Keep harvesting the shoots before they grow more than about 6" high.
In mid spring the growth of any remaining shoots will accelerate at a rapid rate and flowers will start to form. In late spring large numbers of beans will form.
Beans fix nitrogen in the soil as they grow, this is the result of a symbiotic relationship with certain soil bacteria. These bacteria form nitrogen rich nodules attached to the roots and these nodules are at their most nitrogen rich just before flowering. As flowers and later beans develop the plant uses this stored nitrogen up and by the time the beans are mature, the nitrogen is depleted.
Nitrogen nodules on the roots
When grown as I'm describing in this guide, harvest the leaves until early April. Then chop off the tops of the plants and compost them, they make superb compost. Leave the roots and their nitrogen rich nodules in the soil.
For more details on the model that I use for describing harvest periods (first earlies, second earlies etc) please see the chapter on my growing framework