The trials were carried out in 2012 and 2013 at the Estonian University of Life Sciences. Total yield, marketable yield, number of tubers per plant, average weight of tubers, tuber starch content was studied in cultivar 'Ants' (medium late) and 'Laura' (medium early). Following treatments were used: untreated control (T0) Seed tubers were planted directly from storage house (storage temperature 4°C); Thermal shock (TS). Seed tubers were kept before planting 5 days in a room with a temperature of 30°C and 2 days in a room with a temperature of 12°C; Pre-sprouting (PS). Seed tubers were kept before planting 26 days in a room with a temperature of 15°C and 10 days in a room with a temperature of 12°C. From the results in 2012 it was observed that pre-planting thermal treatments increased the number of tubers per plant compared to pre-sprouting. Pre-sprouted tubers gave higher average weight of tubers than in thermal shock variants. Hence, there were lower number tubers with higher weight of tubers in pre-sprouted variants in 2012. The results of experiments (2012–2013) indicated that pre-planting treatments did not have any significant effect on the yield of cultivar 'Ants'. In 2013 the yield of cultivar 'Laura' was significantly increased by pre-sprouting, showing higher number of tubers and higher weight of tubers. Therefore also the share of marketable tubers in the yield of both varieties was higher in pre-sprouted variants in 2012. Therefore, in case of cultivar 'Ants' it could be concluded that the thermal shock increases the number of tubers and decreases the weight of the tubers. The starch yield of cultivar 'Laura' was significantly higher in pre-sprouted variant in 2012. That was due to the significantly higher tuber yield in the same variant
