Effect of Temperature on the Yield and Quality of Broccoli Heads

The effect of temperature on the yield and quality of broccoli heads was determined. The study involved three cultivars: Cruiser, Skiff and Fiesta. The seedlings were planted on five different dates in 1995 and 1996, nine in 1997 and eight in 1998. The length of time from planting to the first harvest for all the 27 cultivation periods was divided into three equal parts determining in this way three phases of growth. The time of harvest was defined as the fourth phase. Temperatures on a scale from 0°C to 40°C were divided into five-degree ranges. Then, for the four growth phases, correlations were determined between the number of hours at a temperature in the five-degree ranges and the total yield, the percentage of loose heads and the percentages of heads with uneven surface or non-uniform buds.

The length of time at a temperature in the range of 15-25°C during the first growth phase after planting and the phase preceding harvest had the greatest influence on total yield. Longer times at temperatures above 20°C contributed to smaller yields. The longer was the length of time at a temperature ranging from 20 to 25°C during the phase preceding harvest and at a temperature ranging from 5 to 15°C during harvest, the lower the percentage of heads with uneven surface was observed. Longer periods with temperatures above 20°C at harvest time contributed to the loosening of heads.