November 15, 2011

"Soilless" soil ?

a near-perfect soilless mix:
equal parts of peat moss, perlite, vermiculite
Many gardeners have worked with artificial soil mixes, sometimes called "soil-less" soils, which is sort of a misnomer. This implies that "real" soil is organic, of the Earth, and only occurs naturally. For most of us, if it's outside in the yard, it's soil. If, according to my Mother, it's on my shoes when I walk in the house, it's DIRT. Perhaps I can shed some light to the idea of artificial soils, and the topic is no small affair to clarify, since there are so many components and mixtures to choose from. Let's look at the most common components.  

One of the most important things to remember is that artificial soils are usually made to grow plants in pots in greenhouses, where plants need a very stable supply of water, and where the plants are produced in a few months to a year at most. These mixes are not very suitable outdoors in the wettest parts of the year. They are often used in propagation beds and with high-demand plants like annuals, Poinsettias, Chrysanthemums, and many perennial plants in small pots.  

The standard of many Begonia and fern growers

Most of these soilless mixes have a finite life in the pot, since the organic components break down, compact, and rob the root system of air. There are other aspects to using soilless mixes for fast-growing, moisture-loving plants, too. In the time that the mix is functional, the plants can grow well, but the grower must realize that as the plants root into the mix, the pots become full of roots, the mix becomes dense with roots, and the plants can choke themselves to death rather fast. One way to increase the life of a solless mix, and thereby increase the longevity of the plant in the pot, is to remove the organic aspect of a mix, leaving just inorganic materials such as calcined clay, perlite, or pumice in the mix. This has become a trend in many propagation bed procedures, where the mix remains intact, and cuttings are rooted in it after the medium has been sterilized between batches of cuttings.     

Calcined Clay
aka Turface, Profile, Quick Dry

Many Bonsai, Cycad, and aquatic plant growers are using calcined clay as part of their potting mixes, and in some cases, using 100% calcined clay  as the sole medium. The water percolation and subsequent air drainage is excellent. This ingredient also hold fertilizer well. many soilless mixtures hold fertilizer very well, a boon to the grower, but a possible hazard to the plant if the mix dries out, leaving high concentrations of fertilizer left in the mix. It is important in any containerized potting mix to occasionally flush the fertilizer residues out of the pot by repeated heavy waterings. Rainwater or distilled water can be excellent for this purpose. 

Soilless mixes, also called "artificial soil" can be a huge benefit to growers of high-demand plants, but growers and hobbyists need to understand the short-comings of the mixes. Inorganic soils can be used effectively, but as with all soil components, each has its quirks. Caveat emptor.

Craig Morell
Pinecrest Gardens


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