Temperature is a factor which strongly affects the yield and broccoli head quality. Temperature determines the date of head initiation and thus affect the length of vegetation period. An experiment the aim of which was to assess the impact of temperature on the yield and the length of the period from the broccoli head initiation until the beginning and end of harvest as well as the length of the harvest period was carried out in years 1997–1999. The seedlings of cv. Fiesta were planted in April, May, June and July. The phase of head initiation was determined on the basis of analyses of microscopic preparations. The highest total yield was obtained from May and June planting dates, the highest marketable yield was recorded in the case of the May date planting. A higher correlation was found between the sum of temperature and mean daily air temperature in the period from the initiation to the beginning and end of harvest and mean weight of marketable heads than between temperature and the total yield. The highest correlation was determined between the mean air temperature and the number of days from the head initiation to the last harvest.

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