Orchid Culture - Questions & Answers from This Month
by Sue Bottom, from the St. Augustine Orchid Society Newsletter.
Email us with any orchid question. If we can't answer it, we'll find someone who can! Send photographs too!
Black Stains on Cattleya Leaf Undersides
Q. I pride myself in having clean leaves but some Cattleya species like violacea or tigrina (and others) seem to get black stains on the undersides of their leaves.
Am I doing something wrong? If not, can it be prevented or is just Mother Nature?
A. That sure looks like fungal spores on the leaf underside. The upper surface of the leaf has chlorotic blotching matching the location of sporing underneath.
There are several leaf spotting fungi that infect cattleyas. When you repot/remount, you can cut away infected tissue. In the meantime, you can spray fungicides like Pageant, Thiomyl/Banrot or Daconil to help prevent the spores from spreading the disease.
How Do You Pot Up Dendrobium Keiki
Q. Can you tell me how to put this dendrobium keiki in another pot?
A. You can cut the cane an inch away from the keikis on either side, soak the roots to soften them and then situate the keiki roots in the pot. You can backfill with potting mix around the roots immediately, or better yet, just add a handful each week so the aerial roots will branch and become acclimated to the mix. It looks like you might have mites on the upper keiki, and the lower keiki may have succumbed to mites, so you'll have to treat for that. The keikis are probably the future of that plant, the mother plant is probably not going to survive.
Divide or Pot Up Cattleya
Q. This is one of my favorite orchids, Blc. Volcano Spring. I want to divide it when it’s finished blooming. It has about 30 pseudobulbs. How many divisions should I try to realize?
A. You could probably get many divisions if you wanted to, but the cattleya has such a short internode distance that you can have many pseudobulbs close together in the pot. You should think about growing it up to specimen size. Select a pot that is an inch or two bigger all around to drop the plant into, once you remove all the decaying old media. If the older leaves were blighted, I'd say cut away the older growths, but those leaves all look pretty good. Unless you want to separate it, think about putting it into a larger pot with fresh potting mix.