During the 2-5 years of cultivation of hyacinth bulbs there are many occasions for an infection by Aspergillus niger. The most important factors are cultivar, bulbsize, damage, temperature, relative humidity, multiplication method and disinfection. The time of grading (= damaging) has a big influence on the number and the type of infections. The temperature before and after the grading affects the number of infections. Disinfection of planting stock and of bulbs used for multiplication can prevent many infections.