24-year (1972-1995) data provided by COBORU (Centre for Cultivar Testing) showed the spatial and time distribution of medium-late and late potato cultivars development stages. A greater variation over 1972-1995, even five-fold, was recorded for duration of potato phenophases than for their dates. The period from potato planting to harvest in Poland shows almost a three-week spatial variation and a significant tendency to get longer, mainly due to earlier planting, emergence and flowering. The dates and duration of respective development stages significantly affect the successive phenophases. Earlier dates and phenophases and the time series can help the forecast of respective dates and duration of phases for medium-late and late potato cultivars across Poland.

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