While I whole-heartedly agree with the first four paragraphs of Oliver Sparrow's discussion, I believe he has overly-narrowed his resolution suggestion:
"To prevent this, grow dry. No plant should be permanently wet unless it is specialised in such environments." I grow much of my collection in semi-hydroponics, which - needless to say - means that they are constantly wet, and I have not experienced any issues with root rot or any tissue attack by microorganisms. I have a quite varied collection under s/h culture, including (but not limited to) paphs, phrags, catts, oncids, cymbids, zygos, phals, and "botanicals" of all sorts, and I would speculate that only the phrags might be considered to fall in the "specialized-to-wet" category. Similarly, I feed constantly, and while I agree that fertilizing does lead to a bloom in microorganism populations, again, I do not see any issues. Some of that may be attributable to my use of inorganic potting media (LECA), but I believe there is another scenario to consider, independent of that: I agree that a plant is not automatically attacked when exposed to microorganisms in its environment. Like most (all?) living creatures, plants develop a "resistance to-" or "balance with" such critters, and unless placed under some stress, the plant and the microorganism population exist in a more-or-less stable "stand-off". Constant moisture does not automatically throw off that balance. The true issue is that of suffocation. When one waters a plant, some of the water is absorbed by the particles of the medium, and some of it - the "bridging" water - is held in between the particles by surface tension. If the medium is made up of particles of varying sizes, whether by design or by decomposition over time, the spaces between the particles are small enough that the bridging water droplets can completely block them, cutting off the pathways for the significant gas exchange that occurs via the root system. (That can also happen with old sphagnum that has become too compressed.) Suffocation, I think we can all agree, is a stress on the plant, and while I don't know if it's enough to throw off the balance with media-borne microorganisms, it will lead to root death (making them fair game for the "bugs"), and further stresses the plant, leaving it very susceptible to all kinds of problems. Grow in a medium in which the inter-particle spaces are sufficiently large, and the water surface tension is insufficient to completely bridge them, eliminating the problem. If that is an inorganic medium as well, it will not decompose and slowly increase its density and reduce the average pore size over time. If you think about it, it seems plausible that the "wisdom" we received as beginners, and some of our various watering schemes are really just strategies we employ to manage the effects of the bridging water. "Let[ting] the medium dry between waterings" allows the bridging water to evaporate or get absorbed by the media particles, relieving the suffocating effect. "Barely moistening the medium" aims at only providing a volume that can be fully absorbed by the particles, leaving none to bridge those spaces. Ray Barkalow - First Rays Orchids - www.firstrays.com Plants, Supplies. Books, Artwork, and lots of Free Info! _______________________________________________ the OrchidGuide Digest (OGD) [email protected] http://orchidguide.com/mailman/listinfo/orchids_orchidguide.com
