In agriculture and gardening, transplanting or replanting is the technique of moving a plant from one location to another. Most often this takes the form of starting a plant from seed in optimal conditions, such as in a greenhouse or protected nursery bed, then replanting it in another, usually outdoor, growing location. The agricultural machine that does this is called a transplanter. This is common in market gardening and truck farming, where setting out or planting out are synonymous with transplanting. In the horticulture of some ornamental plants, transplants are used infrequently and carefully because they carry with them a significant risk of killing the plant. Transplanting has a variety of applications, including: Extending the growing season by starting plants indoors, before outdoor conditions are favorable; Protecting young plants from diseases and pests until they are sufficiently established; Avoiding germination problems by setting out seedlings instead of direct seeding. Different species and varieties react differently to transplanting; for some, it is not recommended. In all cases, avoiding transplant shock—the stress or damage received in the process—is the principal concern. Plants raised in protected conditions usually need a period of acclimatization, known as hardening off (see also frost hardiness). Also, root disturbance should be minimized. The stage of growth at which transplanting takes place, the weather conditions during transplanting, and treatment immediately after transplanting are other important factors. Transplant production systems Commercial growers employ what are called containerized and non-containerized transplant production. Containerized transplants or plugs allow separately grown plants to be transplanted with the roots and soil intact. Typically grown in peat pots (a pot made of compressed peat), soil blocks (compressed blocks of soil), paper pots or multiple-cell containers such as plastic packs (four to twelve cells) or larger plug trays made of plastic or styrofoam. Non-containerized transplants are typically grown in greenhouse ground beds or benches, outdoors in-ground with row covers and hotbeds, and in-ground in the open field. The plants are pulled with bare roots for transplanting, which are less-expensive than containerized transplants, but with lower yields due to poorer plant reestablishment. Containerized stock Containerized planting stock is classified by the type and size of container used. A great variety of containers has been used, with various degrees of success. Some containers are designed to be planted with the tree e.g., the tar paper pot, the Alberta peat sausage, the Walters square bullet, and paper pot systems,