Question
I've been growing orchids as a hobby for over 20 years and have seen most of the standard problems, but this one has me stumped.  I have a small greenhouse (12'x12') in the San Fernando Valley in California.  Temperatures in the greenhouse range from 60 - 110 in the summer and 60 - 80 in the winter.  Light ranges from 100- 2000 foot candles.  Because it can get so hot and dry in my area, I keep the phalenopsis orchids in spaghnum moss to retain some moisture and help with humidity.  I fertilize lightly every other week with a commercial fertilizer (no urea).  I also use this "super food" as a supplement to give B vitamins and some other trace nutrients. I've been using both of these fertilizers for many years with good results.

OK, the problem is this.  All my phalenopsis orchids are growing very small, thick, stumpy leaves.  Plants that used to grow 15" leaves are now growing 2" - 3" leaves.  These new weird leaves grow pretty fast and are almost round in shape rather than elongated ovals.  I'm seeing this phenomenon in all the phals but not the dendrobiums or cattleyas or other types of plants.  I have no idea what could be making the phals do this.  They flowered as usual this Spring, but are still growing these weird leaves.  Something is very wrong, but I don't know what.

I repotted a couple of them today to see if there were any root problems.  No root problems.  The roots are gorgeous!

Any ideas?  I'm out of ideas and I think my phals are running out of time.  Any ideas would be welcome.

Thanks!
---Karen

Answer
Karen, you have me stumped also as I have not heard of this condition.  However, you have the perfect situation to try some experimentation.  First, I would take half a dozen or so of your plants and pot them into a standard fir-bark based potting mix.  Grow them in that mix along side of those being grown in sphagnum.  Feed and water them the same as those in sphagnum. That could test the hypothesis that the sphagnum is at the root of the problem.  Secondly, Set up two more test groups: one group in sphagnum and one in a fir bark-based mix, but instead of using just the one plant food, alternate feedings with 3 different plant foods.  A commercial grower in the Chicago area tells me that he uses several different plant foods in this way to avoid the concentration of micronutrients that are present in a single plant food.  I trust his 6 decades of orchid growing experience to offer this as a possible explanation-- anyway it is worth a test in your greenhouse.  Finally since temperatures can vary so much from year to year, we can't rule out heat stress.  Here again, move several plants into a growing area where the temperature does not get above 85 degrees and see if this yields any improved results.

If you decide to undertake this test, let me know your findings.