For the silage of alfalfa to run properly, it is necessary to set it up quickly and sufficiently. Problems occur when it is raining. The aim of the research was to find out whether the result of fermentation and aerobic stability of the silage could be affected by the addition of a microbial silage preparation in bad weather. Rainfall was simulated by sprinkling the cut with water at a rate of 2 liters per 10 kg. 4 bacterial preparations were applied to the control and experimental cuttings. The silage with higher dry matter (27.3%) had a significantly lower content of proteins and ashes. Silages with lower dry matter (25.4%) had a higher pH and a lower content of lactic acid and acetic acid, which corresponds to a worse evaluation of the fermentation result. The application of bacterial additives did not improve the quality of fermentation. The temperature during the fermentation peaked at 41 °C in all variants, which already represents a great risk of the Maillard reaction. Ensiling with such a low dry matter content is therefore not recommended even if bacterial additives are applied to the silage.