Hydroton and other light weight expanded clay (LECA) medias are widely used here, in South Florida. In our heat and humidity, standard bark deteriorates rapidly and stays too moist during our rainy summers. I've had very good results with any orchids that like to dry out, especially cattleyas. I've had less luck with phals and paphs so I no longer use it for them although some of my friends do. The advantages are that it doesn't deteriorate, it dries rapidly, the round shape leaves room for air movement, It's heavy enough to make pots stable, it doesn't retain fertilizer salts like some other media. The disadvantages would be that it needs to be watered a little more often and it's important to use a complete fertilizer that includes all the micro-nutrients including calcium and magnesium. Orchids can get some micro nutrients from decaying organic media that they won't get from clay media. It's an excellent media for cattleyas.
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