My son did his science fair project last year using catt and phal seedlings that had come out of cell trays. He compared straight small Rexius brand fir bark, the same with 3/4" sphagnum on top, coco fine chunks (a mixture of fibre in 1" lengths and 1/8" chunks), and straight Chilean sphagnum. He weighed the plants before and after bareroot and photographed them before and after. We live in Canada so the greenhouse does get cool in the winter at night: lows of 56 to 60 F. The study went on from late may until the following January. Rain water and Greencare RO/rain water formula fertilizer was used. The results are surprising. Sphagnum was the worst for the phals with the coco clearly the best followed by sphagnum over bark followed by bark. I think the sphagnum kept the roots cooler in the winter and those plants had a reddish caste to them. But the roots in the coco treatment were far superior to any other. For the catts, straight fir bark was the worst. Sphagnum over bark was slightly better than coco followed by sphagnum down the the line. The straight bark produce less than a 1/3 increase in weight while the coco and sphagnum/coco were 90-95% heavier. The interesting thing that showed up on the pictures was that the bark treatment lost nearly all their roots and then had to regrow new ones. It is something that I had noticed previously as I am a commercial grower. If you look at the literature, this is common. Sheenen reported the same thing comparing bark to tree fern and you see people complaining about root loss after repotting catts. I was surprised that the coco turned out so well. I have since switched ny mix to coco, about 1/2 the same amount of bark (the mix blends better that way), a little sponge rock (coarse perlite) and a little charcoal. Since doing this, my plants establish very rapidly running roots to the bottom of the pot, whereas before, they would hit the sphagnum and then often stop before penetrating a year or more later (all the smaller stuff had a layer of sphagnum on the top.) I am also using coarse coco on the bottom of the pots for drainage. Coco holds a lot of water yet does not mush up like bark and stays open. The stuff we get here is supposedly washed and has a low ppm of salts supposedly. It is used by a lot of hydroponic non orchid nurseries. The Rexius bark that we get here is from Oregon and has been steam sterilized and dried. It does not break down very rapidly and dries out fairly quickly. But fresh bark always sucks the nitrogen out. To see what it does to the mix, trying taking each ingrediant and blending it generously into your garden soil in a small patch, then grow some annuals in it. You will find that the ones with fresh bark are sickly and yellow looking unless you pump them with a lot of nitrogen. It may also lower the pH too much. One fix for phals in a cool climate is to use under the bench (actually sitting on the bench) heating to keep the pots (and roots) warmer. You can run a fairly good sized system off of a hot water heater and do not need a boiler unless you have a very large greenhouse. It uses sphagetti tubing recirculating at about 135 F max. and a thermostat. You can put large pots on it without it collapsing and the systems can be bought as a do-it-yourself deal. Jean Allen-Ikeson Windsor Greenhouse Falmouth, NS, Canada
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