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The recent, rare discussion of orchid culture concerning repotting of Cattleyas has been welcome and useful. It has also stimulated me to bring up a culture issue that has been driving me nuts for years. Stated briefly, when I repot
Cattleyas or Dendrobiums that have
been in the pot for 2-5 years, most of the roots in the pots (ceramic slit pots)
appear to be dead. Top growth on
the plants usually appears healthy, and new, white roots with little green tips
are growing at the base of new, vegetative growth. Most of the new roots are external to
the potting medium Most of the
roots in the potting medium are brown and flat. If the potting medium is dry, the
roots are still soggy and wet. Some
can be detached from the plant with a gentle tug. The sheath can be stripped from other
roots with a gentle tug leaving a hair-like central core which I presume is
xylem and perhaps cambium and some phloem.
None of these roots appears functional, although I could be
wrong. The problem is that the
�dead� roots become substrates for bacteria and fungi which can eventually kill
the entire plant. At one time I attributed the
dead-root-syndrome to roots that had been exposed to bark mixes too long. Then I changed to pure red lava rock
which does not break down. Results
have been similar; good top growth
but dead roots in pot after several years. About one year ago I began to use a mix
recommended by someone on this digest.
It is 2 parts lava rock, 1 part fine charcoal, and 1 part washed coco
chips. Plants seem to be doing
better in this mix but the experiment must run for several more years. I have been using another version of
this mix (1 part lava rock, 1 part charcoal, 2 parts coco chips) with some
success for Oncidiums and Phalenopsis in plastic pots. However, these also appear to require
repotting after two years in the pot. I have concluded that under my conditions, it is not possible to keep
Cattleya-alliance and Dendrobiums orchids in pots more than 2 years without
removing all dead roots and starting over.
Same holds true for the Oncidiums and the Phalenopsis that I grow in
plastic pots. I have no problem
doing this since my collection is small (less than 200 plants in various categories), but I�d like to know how
some growers are able to keep specimen plants in the same pot for many
years. My location is: Evans, Georgia, USA, about 33 .5 deg
North, 82 deg West.
My Conditions are: 14ft x 30 ft Turner greenhouse with 63% shade cloth oriented North/South). Yearly temperature range in greenhouse: 58 deg F to 95 deg F. Relative humidity range 34% (brief) to 95% (overnight). Water with tepid ground water that has about 50 ppm dissolved solids. Water frequency depends on conditions; once every 10 days to two weeks in winter; every 5 days in summer. Fertilize with liquid, balanced fertilizers (20-20-20, 100 ppm nitrogen)) every sixth watering in winter, every third watering in spring, summer, fall. Occasional use of Cal-Mag fertilizer at 100 ppm nitrogen. Also apply osmocote (14-14-14) to pots for summer fertilizing in addition to the liquid fertilizer.
In the event that this sounds like too much
fertilizer, I have also had root problems using the weekly-weakly
approach. All suggestions, comments,
etc. will be welcome. Gene
Howard Evans, Georgia
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