The study aimed to establish the timing of the occurrence of the phenophases, as well as their duration.There were observations on the 30th, 60th, 90th and 120th day after offsetting the seedlings. Three development phases wereestablished – 1) from transplanting of the seedlings to the early formation of the roots; 2) growth of roots and 3) intensive growth of root celery until harvesting. In the warmest (extreme) of the three years (2012 ) the phases 1 and 2 had a significantly longer duration, as the formation of roots was delayed by approximately 60 days, compared with the first two years. After the extreme conditions were over during the same year, a „restart“ of plant growthwas observedand of the celery roots respectively and at the end of the vegetation their dimensions were similar to those achieved in the previous two years. A relationship between the average daily air temperature and the duration of phenophases (R>0.9) was estabblished.