The paper presents the results of studies concerning the effect of the period when potato tubers were exposed to microwave irradiation on potato (Solanum tuberosum L.) growth and yields. The studies were conducted over three consecutive years (2007-2009) in southern Poland. The experimental plots were established as randomised blocks in three replications. The reaction of three very early potato varieties (Felka Bona, Rosara and Velox) to microwave radiation was studied. One level of microwave irradiation was applied (it was produced by a generator operating at 100 watts of power, for a period of 10 s). The following variables were considered as independent: the year of research, the potato variety and the period of irradiation of potato tubers (before storage, after storage, and before and after storage). During the vegetation period measurements of plants growth, development and yields were carried out. The following parameters were considered as dependent variables: number of main shoots and their length as well as the weight and number of tubers in the yield. A significant impact of the period of potato tubers exposure to microwave irradiation on the number and length of shoots as well as on the tubers yield per plant was observed.