When speaking of vegetables most people picture the annual plants grown for their fruit, tubers, leaves and stems. Annual plants die after flowering and producing fruit or seeds. Perennial plants do not die after flowering or producing seeds, nor do they die with the onset of cold weather (the above ground leaves and stems may die back, but the roots and crown survive). There are hundreds of perennial vegetables, several more well-known than the rest.
Well-maintained, established asparagus beds can produce for 50 years or more. Asparagus is an early spring/summer crop. The spears or newly emerging stalks are harvested when they are about 8 inches tall with the diameter of a No. 2 pencil. It takes three to four years for a newly planted asparagus bed to become established and produce spears.
Artichokes are tricky plants: they may be either annuals, biennials (producing fruit the second year) or perennials. Perennial artichokes only grow in USDA hardiness zones 7 and above. Perennial artichokes will produce fruit for four to six years (usually from offshoots of the parent plant). Replace these short-lived perennials with new plants when harvest levels drop or when the plant no longer produces artichokes.
Rhubarb forms a mound of stalks and leaves 3 feet in diameter and 3 to 4 feet high. Only the stalks or stems (usually red but sometimes green or purple) are eaten; rhubarb leaves are poisonous. Rhubarb prefers zones 7, and below although there are now varieties available that tolerate warmer zones. Harvest rhubarb stalks from mid to late spring through mid-summer.
Horseradish produces a pungent tuber used to flavor condiments, meats and fish. Horseradish thrives in zones 3 through 7 or 8. Harvest the tubers in late fall through early spring after the foliage has died back to the ground.
Sorrel is a tasty spring green that grows well in zones 1 through 10. Harvest tender young leaves first for use in salads. Larger leaves must be cooked before eating as they may become bitter. Use the larger sorrel leaves in soups and stews or saute lightly in butter or oil until they wilt. Sorrel is another spring vegetable. Harvest the leaves from early to mid spring.