Seeds and transplants are not the only methods to raise new plants. Some vegetables are started from other plant parts: suckers, tubers, slips, crowns, sets, cloves, divisions, or cuttings. In some cases plants can be grown either by seed or from plant parts. Onions, for instance, take a very long time to germinate from seed, so it usually makes more sense to grow them from sets. Other plants grow best from plant parts.
Suckers, or offshoots, are plants that grow or shoot up from the root system of a mature plant. These suckers can be dug up and divided from the mother plant, and then transplanted to mature into new plants. Globe artichoke is usually the only vegetable grown from suckers.
Tubers are specialized swollen underground stems capable of producing roots, stems, and leaves. Irish potatoes and Jerusalem artichokes are usually grown from tubers. When the plants are cut up for planting, as in the case of Irish potatoes, they are called seed pieces.
Slips are young, tender, rooted cuttings or sprouts grown from vegetable roots. Sweet potatoes are the only vegetable commonly grown from slips.
Crowns are compressed stems near the soil surface that are capable of producing leaves and roots. Crowns that are planted with the roots attached are referred to as "roots." Crowns are divided from the mother plant when the plant is dormant. Asparagus is grown from crowns.
Sets are one-year-old onion seedlings that were pulled when the bulbs were young. The bulbs are air-dried, stored for the winter, and planted next spring.
Cloves are the segmented parts of bulbs. Garlic is the only vegetable commonly grown from cloves. Each garlic bulb is made up of a dozen or more cloves, and each clove is planted separately. For the highest yield, separate the cloves as you plant.
Divisions occur naturally in the form of small, rooted plants or bulbs that grow from the mother plant. You separate or divide them off to grow as individual plants. Dig up the mother plant, separate the small new shoots, and replant each new unit. Horseradish and rhubarb are grown from divisions. You can divide plants in the spring or the fall. Fall is preferable because the cool, moist weather helps the plants become well-established.
Cuttings are started by cutting a piece of stem from the plant at the node -- the lumpy place on the stem where leaves are attached -- and forcing it to develop new roots. This is best done in early summer, when the stems are actively growing. Treat the cut end of the stem with a commercially prepared rooting hormone and stick the cutting in moist soil away from direct sunlight. New roots will form in a few weeks, and the new plant can be placed in the garden. Tomato shoots are often rooted for a late crop.