This term is sometimes applied to the practice of growing plants in soil-filled barrels with holes made in their sides. In the holes, and in the exposed soil at the top of the barrel, too, suitable plants are set. All, or some of the ones used, are trailers, which ensure that the sides of the barrel will be well clothed with foliage.
The holes are usually 2-4 in. in diameter, are spaced 12 in. or so apart, and are located regularly or irregularly along the sides of the barrel. After the holes have been drilled, the barrel is set on end; 6 in. of broken brick or other drainage material is placed in its bottom and is covered with straw or grass sods turned upside down. The barrel is then filled with a rich, porous soil mixture. A satisfactory one consists of equal parts rich loam, coarse sand, and leaf mold, peat moss or humus with coarse bone meal added at the rate of a pint to each bushel. The plants are set in place as the filling of the barrel with soil proceeds. To provide a means for watering, and added assurance of drainage, a 6-in. perforated pipe is inserted through the center and is filled with sand.
Strawberries are a favorite crop for growing in barrels; but many rock garden plants and plants of a succulent nature offer other possibilities for growing in this way. Among the succulents are Sedums, Echeverias, Sempervivums and others; among the rock garden plants, Thymes, Arabis, Potentillas, Helianthemums, and Veronicas.
Especially made earthenware pots or barrels, with openings (pockets) in their sides for planting, are sold and are highly decorative when appropriately planted. They represent a variation of the wooden barrel with holes drilled in its side that is described above; they may be planted in the same manner.