January 2013 - Potting Media

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Given the popularity of orchids, it is hard to believe that one of the biggest issues for orchid hobbyists today is obtaining media. Most of the difficulties I have had the past few years relate to poor quality media or to the unavailability of some previously popular media. Florida’s warm temperatures pose problems for organic media and Aliflor and lava rock have proven to be ideal both for the climate and for my lack of interest in repotting. Aliflor is no longer available and I haven’t found a substitute with the same qualities. Several friends have suggested various plastic products that shed water. Stalite is another product that has been suggested, but it does not come in a large size as its intended purpose is as a light rock to mix with cement. If nothing new is found before repotting begins in April, one of these products may be the solution.

One would expect that the use of sphagnum by the pot plant trade would mean that there would be a good supply of that medium. However, the quality has become so poor that finding good sphagnum has become difficult. The last bale of Chilean sphagnum looked fine, but disintegrated within six months while the previous year’s sphagnum remained relatively intact on the same bench. Finally, I found a supplier for New Zealand sphagnum. It was three times the cost, but is clearly much higher quality. There is even better New Zealand sphagnum available if you are looking for the longest, freshest strands. If you are uncertain how to tell quality of sphagnum there are several things to look for. It should consist of strands of moss that are at least 6” long. If there are lots of tips or broken pieces you likely have poor quality material best used for garden plants. Another technique is to just soak it for 24 hrs and then pull strands from both ends. Leave the material moist and test it each week the same way. The poor material I used offered no resistance after a month, however, New Zealand sphagnum remained strong.

Several commercial growers told me that they could not afford the high quality sphagnum and had switched to a mixture of charcoal and large sponge rock, which is a soil aerator. Plants I have had in this mixture are doing well after a year, but I have some issues with using charcoal derived from cutting and burning rain forest trees.
What is the ideal medium? A product that was inexpensive, decomposed slowly, if at all, and did not leach salts or produce extreme acidity or alkalinity in the pot would be nice.
Ideally, it would be light, so that shipping would be less expensive and be useful in the garden when discarded. Where are the entrepreneurs when you really need them?

The first incident of rot showed up last month on phal leaves. This is a common occurrence each year on new phals and even some newly purchased cattleya seedlings. Orchids grown under high nutrient conditions are prone to this soft rot, easily identified because affected tissues look watery. Such rots spread quickly and must be treated before reaching the meristem in the crown, which can kill the whole plant. Remove the infected area and be sure to cut well inside the healthy living tissue, to be sure the rot is removed. Put some cinnamon powder on the cut. After such an infection, I also spray the orchid and surrounding plants with hydrogen peroxide each time after I water to be sure there are no spores germinating. I do this for a couple of weeks after treating an active rot infection.