Plants that are confined in containers do require soil or some other substance wherein they could anchor their roots.
More often than not, it is from this material that the plant will get most of its food. Good garden loam comprises roughly of about 25 per cent clay, 35 per cent sand, 10 per cent organic material, plus the balance in moisture and air. A soil like this having a mixture of both fine and large pores provides free drainage, yet has a good water-holding capacity. Soil with too heavy clay content will produce puddle and drain poorly; too dry soildrains freely and dries out quickly. Organic material mixes the two into a fertile, permeable soil. Compost, leaf mold, and peat moss are among the organic or humus-making materials. Peat moss, which can be easily obtained from plant counters, is the one most of us depend on to make an acceptable potting soil.
Fir bark that is ground in 1/4 to 1-inch particles are usually used for potting orchids and bromeliads, other epiphytic plants, and some gesneriads like columneas.
Other materials frequently added to potting mixtures are horticultural grade expanded mica (one trade name is Vermiculite, so widespread that it is used as a common noun), sphagnum moss, and pebble-size horticultural-grade perlite, which most plant hobbyistspertain to it as sponge rock, though there is a trademarked product made out of perlite which is called Sponge Rock.
Vermiculite, sphagnum moss, and perlite really make good additions to potting soil or they can be used alone or in mixtures to propagate plants. By adding nutrients, they can be used for growing plants too. Generally when mixing potting soils, feel free to substitute vermiculite for leaf mold (both allows the soil to become spongy and help keep it well aerated), and perlite for sand (perlite is feather-light, and are easy to carry around the home and garden as compared to sand). Adding up some ground charcoal to your potting soil makes it more porous and keeps it fresh, or "sweet" as our grandmothers might have said.
© 2012 Athena Goodlight