Since the summer of 2013 and earlier, the use of “Lava Rock” as an orchid medium has been actively discussed in the orchid community in general, and among members of both the Jacksonville Orchid Society (JOS) and Saint Augustine Orchid Society (SAOS).
My interest is a result of searching for a Hydrotron replacement after closure of the company that made the product for 27 years. In doing so, I’ve found two easily available replacements, Lava Rock and PlantiT, both of which I’m evaluating. There are other replacements available as well, but these can be found in the local area with Lava Rock being clearly the cheapest.
At this time, I’ve only heard of one person using PlantiT, which is available in Jacksonville at Grower’s Choice (http://www.hydroponicsgc.com). While I don’t yet have enough data, my initial assessment is that PlantiT, although smooth in configuration like Hydrotron, is far more water retentive than Hydrotron or Aliflor. In my own adhoc testing (decidely non-scientific) PlantiT appears to remain wet 2-3 times longer than a comparable quantity of Hydrotron. PlantiT is also far more dusty than Hydrotron out of the bag and should probably be washed before use. Unfortunately, while using PlantIt, I’ve already lost one orchid (a Cattelaya type) to rotted roots. Moreover, when examining the media I noted it was exceedingly wet, although the plant had been watered two days previously.
Regarding Lava Rock, Cortney Hackney and others report good results and I can make the same report as well. In my case, both Dendrobia and Cattleya appear to do well with robust root growth under my growing conditions. Successful use of Lava Rock with orchids is reported elsewhere on the Internet as well. Tom of the Angraecums website (http://www.angraecums.blogspot.com/2013/08/lava-rock-as-potting-medium-pros-cons.html and on Facebook at https://www.facebook.com/tkangraecums) reports generally good results with Lava Rock, but also notes that in larger pots (8 inches and larger) the center may be too water retentive.
At the moment, it appears Lava Rock has the nod as a replacement for Hydrotron in many of my applications. How about yours?