Lupins belong to the so-called green manure varieties. However, this applies less to the perennial plant kept in the garden as an ornamental plant. Special lupine varieties are sown for green manure, which is later simply cut and dug under.-
Lupins are relatives of peas and beans
The relationship between peas and beans can be seen from the shape of the pods that the plants form after flowering. Like all legumes, lupins not only develop very long roots.
They also live in symbiosis with certain bacteria found in nodules on the roots. These bacteria produce nitrogen, which they give to the plant.
As a result, lupins also grow well on very sandy and poor soils. They improve the soil sustainably because they in turn release the nitrogen and thus provide new nutrients.
The effect of lupins as green manure
- Soil loosening by roots
- nitrogen enrichment of the soil
- Soil fertilization by undermining foliage
The roots that the lupins develop as green manure can grow up to two meters long. They dig into the ground and loosen it up deeply.
The bacteria in the nodules ensure a good supply of nitrogen, first to the plant and later to the entire soil.
The green manure lupins are cut off after a while and buried in the ground. Both the leaf material and the roots remain in the soil and decompose there. As a result, they release nutrients that improve the soil significantly. At the same time, they loosen it up well.
Green manure late in the year
The big advantage of growing lupins as green manure is that the plant is hardy and can be sown late in the year.
Unlike other green manure plants such as phacelia (bee pasture), the plants do not freeze immediately but continue to grow at relatively low temperatures.
Lupins are therefore often sown as green manure in the vegetable garden after the vegetable beds have been harvested.
Lupins are playing an increasingly important role in supplying protein through food. They are therefore often grown as a substitute for soya. However, only sweet lupins are suitable for consumption, because the popular ornamental lupine is one of the poisonous plants.