Home > Semi-Hydroponic Culture > Inert Media Comparison
During the development of my Semi-HydroponicTM orchid culture technique, it became apparent that the successful use of inert media was directly connected to three factors: 1) free air flow to the root zone, 2) maintenance of a constant supply of moisture and nutrients, and 3) stability of the medium in the pot. Free air flow to the roots is, of course, and important consideration in all orchid culture, but the other two criteria require additional thought as these media do not absorb as much moisture as organic media, on a weight-for-weight basis, and cannot be compressed in the pot to anchor the plant.
My original experiments utilized #1 "horticultural grade" perlite that had been rinsed and then screened to provide essentially 100% of the particles around 1/4" in
diameter. That medium proved to be acceptable only with pleurothallids and other fine-rooted plants, as well as cymbidiums that are known for their tolerance of more "terrestrial" type media. Later, a combination of #4 sponge rock (perlite) and medium grade charcoal in a 50/50 mixture by volume proved better. With particle sizes for both materials in the 1/2" to 3/4" range coupled with their irregular shapes, my success criteria appeared to be well met, and indeed, many more types of plants thrived.
Unfortunately, the sponge rock was light and quite buoyant, resulting in the medium floating whenever it was watered, and plants tended to get "unseated" unless they were well established in the pot. The addition of a gravel top layer reduced the tendency, but the gravel tended to mix into the medium, defeating its purpose. Over time, I also noticed two negatives with that medium: the growth of roots and handling of the potted plants led to disintegration of the sponge rock, which restricted air flow to the root zone, and the medium tended to accumulate salts.
Then I discovered Lightweight Expanded Clay Aggregate (LECA) ceramic media, and my overall success rate began to be acceptable.
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