June 2011 - Dry Heat and The Roach Trick

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Once again, summer starts with high temperatures and low humidity. Windowsill growers and those with greenhouses are experiencing the same phenomenon as air conditioners strip moisture from the air to keep us cool inside, while daily heating outside lowers humidity in greenhouses. June is also the month when light intensity peaks.

How well your orchids tolerate this time of the year depends on how well you have prepared them over the previous winter and spring. A good root system allows your orchids to absorb and store water making extremes tolerable now. Pay careful attention to small seedlings or newly repotted orchids, which have the least tolerance for extremes. Placing orchids with potential water stress in lower light can help them tolerate the lack of water as they grow new roots. A little extra water might also be necessary, but high heat can encourage rots of various kinds.

A problem last summer that left some of my favorite cattleyas vulnerable to desiccation this summer was finally solved with a simple trick. The problem was most acute on cattleyas newly repotted or on those that only get new roots once a year, e.g. many bifoliate cattleyas. Large, roaches (Palmetto bugs if you are from Florida) were eating new roots at night as they emerged from new growths, effectively killing the root growth for the year.

Growing in lava rock has been a success except for this issue. Attempts to kill roaches by drenching with a solution of liquid Sevin were only moderately successful, since the large spaces between chunks of rock provided a refuge for at least a few roaches.

The only obvious alternatives were to either switch to a finer medium or use a very strong pesticide that might damage orchid roots too. What worked was to squeeze all of the water out of a handful of damp New Zealand sphagnum and to shove the moss under the newest growth before new roots emerged. Not only did this prevent roach damage to new roots, but roots, once in the sphagnum, branched and quickly grew out of the moss into the rock below. It has the added benefit of providing an easy way to know when to water. When the moss is very dry it is time to water.

The plan will be to remove the moss next year as I curate my collection and decide which orchids to repot, which to keep, and which to discard. Curating one’s orchid collection is one of the most difficult facets of orchid growing. Hobbyists new to growing orchids often do not have to deal with this until they figure out how to grow and multiply their orchids and also run out of space, which happens quickly once the first problem is solved.

Extra divisions and spare orchids are never hard to get rid of, especially if they are in good shape. Even backbulbs are welcomed by new hobbyists, especially if they are something special. I put backbulbs from great cattleyas under benches to see if they will sprout from an old eye. If they do, I check to be sure the front lead is doing well and if it is, find a good home for the backbulbs.
Repotting this time of year is still fine as long as care is taken to be sure that newly repotted orchids are not overly stressed by heat and lack of water.