One more way, add organic matter to the soil, which, however, is rarely used in allotment gardens, is the green manure.
It can be integrated very well into the crop rotation as a second or catch crop and helps, especially when there is a shortage of manure, compensate for the humus deficit. Phacelia is the most suitable green manure plant, which is also an excellent bee pasture. But also mustard, Lupine or Vetch rye can be used. Sowing usually takes place between the end of July and the beginning of August, digging in late autumn, Vetch rye only in the following spring. Where it can be set up, you should definitely order one or the other area with green manure plants.