A charming lupin that combines ornamental beauty with agronomic benefit: its blue and/or white flowers attract pollinators while the roots enrich the soil with nitrogen.
About the variety. This annual variety, with spikes of lipped flowers in deep blue and/or white, is an excellent nitrogen fixer, recommended as an intercrop green manure.
Itinerário técnico
Como cultivar narrow-leaf lupin?
Um guia de cultivo passo a passo, da sementeira à colheita.
pH ideal 5.0 to 6.8Temperatura ideal 10 to 25 °CCompasso Broadcast, not in rows. About 15 to 20 g per square metre
Sementeira
Broadcast over worked soil and cover the seed with three to five centimetres of earth, or sow in rows at that depth: the seed is large and on the surface it dries out or gets eaten. Sow generously, because the aim is to cover the ground completely and leave no room for weeds. Sow in late summer or autumn to cover the winter, or in spring for a short cover between crops. Water after sowing if the soil is dry. If the ground has never grown lupin, mix the seed with soil from a field where it has grown, or with the proper inoculant: without the right bacteria it fixes no nitrogen.
Solo
It wants acid to neutral soil, sandy or loose, at a pH between 5.0 and 6.8, and fails on limy ground: there the leaves yellow and the plant stays stunted. It needs no feeding: its whole role is to improve the soil, fixing nitrogen, structuring the ground with its roots and shielding the surface from rain and sun.
Clima
Very tough and adaptable, between 10 °C and 25 °C. In southern Europe the useful window is autumn and winter, when there is rain and the soil would otherwise lie bare. In France and Germany sow in spring, from March to April, because winter is too cold for the plant to stand outdoors. Sow while the soil is still warm, so the crop covers the ground within three or four weeks: a late sowing, with the cold already in, comes up thin and does not do its job. The same calendar applies in Italy: conditions in the centre and south are close to those of southern Portugal and Spain, and those of the north to central France. In spring, sow as soon as the ground can be worked and cut before the June heat, because after that the material turns woody and the plant runs to seed.
Fertilização
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.
Rega
Water only to secure germination. Once established it needs no irrigation in almost any situation and lives on rainfall. A green manure that is watered heavily loses much of its point.
Controlo de Infestantes
Sown densely, the crop covers the soil itself and keeps weeds well in check. The work is concentrated in the first two or three weeks: hand weed or run a hoe very shallowly between the plants. Avoid disturbing the soil once the canopy closes, so you do not damage roots or bring fresh weed seed to the surface.
Controlo de Pragas
It has practically no relevant pests and instead shelters beneficial insects and pollinators through the off season. Watch only for slugs at the seedling stage and for birds, which eat seed left on the surface: cover the seed properly when sowing. Rabbits and pigeons like the tender seedlings: in a small garden, light netting for the first three weeks stops you losing the sowing. Aphids can appear at flowering in dry years, but rarely justify treatment: the ladybirds deal with them.
Doenças
Anthracnose, carried on the seed, is the serious disease of lupin: it causes sunken stem lesions and twisted pods; use healthy seed and do not repeat lupin on the same ground within four years. The important precaution is rotational: choose a species outside the family of the crop that follows and of the one that has just left, so you do not multiply soil borne disease. After brassicas, for example, avoid mustard and fodder turnip. In very dense sowings and wet winters collar rot can appear: do not water and do not sow thicker than recommended.
Colheita
Let it flower: the spikes draw bees and bumblebees for four to six weeks in spring, and can be cut for the vase when the lower third of the spike opens. For seed, wait until the pods turn brown and dry, in early summer, and pick them before they burst, because they open on their own and throw the seed far. Store the seed in a dry jar; this variety is grown for its flowers and for the soil, not for the table. If you want it as a green manure, cut and incorporate at the start of flowering. The reference colour is blue and/or white, and that is what tells you it is ready.
