Leafy vegetables that are generally eaten uncooked in salads include lettuce, celery, endive, dandelion greens and parsley. Lettuce and endive are planted in April and again in late July. Few people actually plant dandelion for greens, but some who do not use chemicals on their lawns harvest the young leaves of the weed in the spring and fall. Parsley is a cool-season crop and grows best in the spring and fall. Cooked greens include spinach, which is planted as a spring crop in April and a fall crop in August.
True spinach begins to flower in warm weather, although some varieties are slower than others.
New Zealand spinach is not a true spinach, but it tolerates hot weather better than spinach. Chard, also known as Swiss chard, is heat-tolerant and produces greens from July to October. Leafy vegetables, like root Crops, can be harvested whenever there's enough of the vegetable to make it worthwhile. However, there is a generally accepted ideal size and form for each vegetable. Pick leaf lettuce when the leaf is large enough to cover a salad plate and cabbage when the head is firm.