Vegetables can be categorized into warm-season and cool-season vegetables based on the range of temperatures that they will grow in.
For gardeners in temperate areas, warm-season vegetables can be grown in spring and summer, while cool-season vegetables will grow best during fall and winter.
Gardeners in low-elevation tropical or sub-tropical areas may be able to grow only warm-season vegetables. On the other hand, gardeners in tropical or sub-tropical regions at higher elevations will be able to grow cool-season vegetables, sometimes almost all year long as the temperature is constantly on the lower side.
Warm-season vegetables are those that prefer to grow within a temperature range of about 18-30°C (64-86°F) and mainly include fruiting vegetables.
Some warm-season vegetables, such as tomato, pepper, eggplant, corn, legumes, and most gourd vegetables can tolerate temperatures across the full range from 18-30°C (64-86°F).
However, certain other tropical warm-season vegetables, including sweet potato, okra, yams, and cassava, are only able to tolerate temperatures within a higher but narrow range of 21-30°C (70-86°F) and won’t grow as well when temperatures are below this range.
All warm-season vegetables are affected by chilling damage if exposed to temperatures below 10°C (50°F) for an extended period of time and are not cold-hardy.
Cool-season vegetables grow within a temperature range of about 10-18°C (50-64°F) and mostly include leafy vegetables, root vegetables, and stem vegetables. Cool-season vegetables can also be divided into two distinct groups based on the temperature range that they can tolerate.
One group of cool-season vegetables has an optimum temperature range of 16-18°C (61-64°F). This group can be further divided into vegetables that can tolerate some freezing and those that are damaged by freezing. Spinach, beetroot, cabbage, broccoli, kale, Brussels sprouts, and collard greens are freeze-tolerant vegetables. Conversely, although potato, celery, lettuce, and cauliflower have the same temperate range, they can be damaged by freezing temperatures.
The other group of cool-season vegetables, which includes onion and asparagus, tolerate a larger range of temperatures from 18-30°C (64-86°F) and have some freeze tolerance, making this group of vegetables overlap with warm-season vegetables and enabling them to be grown in warmer areas as long as night time temperatures are low enough.
Furthermore, the actual temperature range that’s best for a vegetable plant may vary slightly based on the variety as well. This categorization can be used to decide which vegetables you could grow in your vegetable garden this season.