Where seasons are distinct, gardeners traditionally grow warm season vegetables during the summer months while cool season vegetables are more commonly grown in the cooler part of the year. The root systems of cool season vegetables are commonly shallow; their seeds germinate at cooler temperatures and in general, are more adapted to grow in cooler weather. In addition, the harvested crop is more tolerant to chilling injury.
In Hawai’i there is the opportunity to plant and harvest many different kinds of vegetables all year long. However, some vegetable plants will definitely do better when planted within a given time frame. Late summer, early fall is a good time to begin planting cool season vegetables: beets, broccoli, cabbage, carrots, celery, chard, kale, leaf lettuce, onions, peas, potatoes and turnips.
Some vegetable crops run into trouble when planted out of season. Lettuce is a good example. It is a cool season vegetable and as long as the temperatures remain cool, the lettuce plants will continue to produce tender leaves. Generally lettuce is planted from September through March. During the hot summer months the plant bolts, that is, begins to flower and seed. This principal is also true for other vegetables like broccoli and head cabbage. Gardeners living at higher elevations may be successful planting some of the cool season vegetables such as cauliflower, chard and mustard in late spring and summer.
Experiment with a wide variety of vegetable plants, even warm season vegetables in the winter and cool season ones in the summer. You will soon learn what works best for your climate zone.