To guarantee a long-lasting and steady delivery to the market, a sufficient part of the crop should be put in the storehouse. Pre-condition for successful storage is, first of all, the use of suitable varieties (s. list), especially, since in Germany the treatment with MH 30 for the prevention of sprouting has been forbidden.
Exact trials to determine optimum storehouse conditions are not available. According to experience in Austria, the Netherlands and Denmark, the optimum temperature oscillates around +/- 0° C. As the onions emit water and produce heat when they are stored, they should be ventilated with cooling air (relative humidity 65% – 70%) from time to time. The cooling temperature mustn´t be below -1° C, since the freezing point of the onions is at -1,5 °C.
To avoid the production of condensation moisture, it is of vital importance that the temperature of the ventilation air is not higher than that of the onions. A steady supervision of the storehouse by means of temperature sensors is recommendable. Storehouse rot and the inclination to sprout mean increased biological activitiy, which results in temperature rises.
The onions are stored in large boxes or loosely. The best method is determined by the farm and the marketing structure. Generally, loosely storaged onions (2 -3 m max) can be ventilated more easily and exactly. Large boxes, on the other hand, prevent that infections are spread. Besides, smaller quantities can be taken from the storehouse without disturbing other parties. Without cooling measures, the storage life generally ends in February. With sufficient cooling the onions may be stored until April/ May.