Crisp-head lettuce takes longer to mature and is harvested when the head is full size and moderately firm. Beets and turnips serve a dual purpose. Tops can be used during the thinning process while the remainder of the plants are left to develop into a root crop for later enjoyment. If only the tops are desired, seeds can be scattered in a corner of the flowerbed or garden and used as soon as they are 4 to 6 inches tall. The tops of these vegetables are an excellent source of vitamins A and C, B vitamins, and calcium.
Mustard greens mature quickly and are best planted in early spring or fall.
Warm, long days will cause the plant to go to seed. Harvest before the leaves are fully grown for best flavor. Spinach will also go to seed quickly during long days. Plants are best grown in early spring or late summer for a fall crop. Harvest as soon as leaves are 6 to 8 inches long and allow the center of the plant to continue producing.