Itinerário técnico
Um guia de cultivo passo a passo, da sementeira à colheita.
Sow direct five or six centimetres deep in rows. Germination takes ten to fifteen days. In southern Europe it is sown in autumn to crop in late winter and spring; in the north, in late winter or in February and March. Autumn sowing gives sturdier plants and dodges the peak of the aphid season.
It adapts to almost any soil, heavy ground included, as long as it does not waterlog, at a pH between 6.5 and 7.5. No nitrogen fertiliser. It leaves the soil structured and enriched, making it one of the best crops to open a rotation.
It is cold hardy and takes several degrees of frost, above all when autumn sown and well rooted. It grows between 10 °C and 20 °C. Heat above 25 °C stops flowering and brings aphids and rust on in force. It takes cold well and a light frost even improves the flavour, which makes it an autumn and winter crop in southern Europe. On the Portuguese coast it grows through the whole winter without trouble. Inland in Portugal and Spain night frosts do it no harm, but the summer there is too hot and dry for it. In France and Germany it is a summer and autumn crop, and in a cold winter a fleece or a low tunnel keeps the leaves in good condition well into the cold season. In Italy it is an autumn and winter crop in the centre and south, as in Portugal, and a spring and autumn crop in the north, where the Po valley winter is too hard to leave it outside unprotected.
It fixes its own nitrogen through root nodule bacteria, so it should not be given nitrogen fertiliser. Add mature compost only if the soil is poor and, if needed, a little wood ash for potassium. Feeding nitrogen is the classic mistake with this crop: it produces huge plants with few pods.
It needs little water in winter, and in the south rainfall usually suffices. Step watering up at flowering and pod fill, when a shortage cuts the crop most.
Hoe often and always shallowly, because the roots are short, near the surface and break easily. The best method is to prepare the bed two or three weeks in advance, let the first flush of weeds germinate, remove it and only then sow: that gives you a decisive head start. A thin layer of sieved compost between the rows greatly reduces later work.
Black bean aphid swarms the tips in spring and is the decisive pest. The traditional and effective answer is to pinch out the plant, cutting the top fifteen centimetres as soon as the first pods set: this removes the tender tissue where the aphid gathers and sends the energy into the pods. Follow up with potassium soap. Bean weevils drill round holes in the dry seed: freeze saved seed for forty eight hours.
Chocolate spot covers the leaves with rounded brown blotches in wet winters and is the commonest disease: space well, avoid excess nitrogen and do not sow too densely. Rust appears late in the cycle as orange pustules. Use a four year rotation away from other legumes.
For fresh use, pick when the beans are formed but the pod is still green and the scar on the bean is white rather than black: after that the bean goes mealy and the skin tough. Very young pods can be eaten whole. For dry beans, let them dry fully on the plant and thresh in dry weather. Cut the plant off and leave the roots in the soil, for the nitrogen. The reference colour is light green, and that is what tells you it is ready.
