Commercial potting mixtures are ideal for container plants. These are referred to as “soilless mixtures” because they do not contain soil but rather various combinations of vermiculite and peat moss as well as either perlite or ground pine bark. The latter two components are used to improve drainage and aeration. The better commercial mixes are also fortified with fertilizer and lime as well as a wetting agent. Commercial mixtures are recommended for gardeners who require only a few cubic feet for container plant needs.
Those who plan to grow a considerable number of container plants may prefer to prepare their own potting mixture. Good field soils can be used for this purpose. Blend sandy or clay loams with organic matter to improve the necessary drainage characteristics.
Numerous formulas are effective, but a mixture of 50 per cent soil and 50 per cent organic matter works well. One of the best organic matter amendments to use is ground pine bark having a finer particle size. Nurseries usually have this size bark on hand for their potting needs. Either fresh or composted pine bark is acceptable. Compost hardwood barks before use.
Peat moss also can be used as the organic matter amendment. The coarser type peat moss is recommended. Avoid fine, muck type peat mosses. They decrease aeration and drainage rather than improve it
Because of its characteristics, peat moss absorbs and holds a considerable amount of moisture. This could be detrimental when it is mixed with soil and used in containers exposed to extended rainy weather because the potting mixture could hold excessive moisture. Consequently, it is advisable to add perlite to a soil/peat mixture.
Perlite, a white, heat treated expanded mineral, improves the drainage properties of the mixture. A ratio of two parts soil, two parts peat moss and one part perlite should be satisfactory.
