Vegetable crops

a) Cabbage and cauliflower: Cabbage is grown to some extent in every country in the subtropical and temperate areas of the world. Cabbage grows best when monthly mean temperatures are between 25.5 and 21oC. It approaches the head stage slowly at a mean temperature of 13 to 15.50C, and can stand market supply for many days at a mean temperature of about 10oC. This permits the long harvest period of good quality cabbage. It withstands frost in the fall or winter in the head stage, but freezing is generally destructive. When the mean monthly temperature exceeds 21oC, growth becomes slow and abnormal and the quality is usually poor.

b) Tomato: The temperature requirement of tomatoes differs at different stages of its growth. Germination of tomato seeds commences when the soil temperature is 14-160C. Research shows that day/night temperature of 26.5/20oC is optimum for vegetative growth. Reduced growth rate of plants is observed at soil temperature below 17oC and air temperature below 20oC. The growth stops when the air temperature drops to about 8oC. High temperature of 30 to 35oC especially when accompanied by low relative humidity cause large scale flower dropping. Fruit setting is higher and fruit size larger at a temperature approximately 18oC. Below 10oC, no fruit setting takes place. The optimum temperature for ripening of tomatoes is 20-25oC. Tomato plants require large amounts of light; shading produce low yields.

c) Cucumber: The cucumber is a heat loving plant. Below 12oC cucumber seeds do not sprout; at 18oC sprouts appear slowly (within 8 to 10 days) and at 25 to 30oC they appear within three to five days. Seed sown very early in the cold and humid soil will not germinate. The optimum temperature for its growth is around 25oC. Cucumbers also require a high atmospheric humidity and a fairly humid soil. When an air temperature falls below 14oC, the plants turn yellow and growth stops.