Orchid Culture - Questions & Answers from This Month

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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!
 
Spots on Vanda Flower

Spots on Vanda Flower

Q. I recently purchased some more orchids (a recurrent problem) and one was a blooming vanda that had questionable spots on the flowers. I wasn’t going to buy it as I was worried about Botrytis but I broke down and bought it anyway.
A. I think what you are seeing is edema on the flowers, in which the spots are raised and look a little corky. Edema is like a blister when the plant absorbs more water than can be shed through transpiration, so it blisters. It happens more on leaves than flowers. It happens when you water late in the day and the nights turn cool or when you water on a gray rainy day. It doesn't really harm the plant.   (Jul-20)
 
 
Snow Mold in Bark Mix
Snow Mold in Bark Mix

Snow Mold

Q. This explains my dead Cattleya! And we aren’t even in the rainy season! Lesson learned…just because the water is running out of the clay orchid pot, it doesn’t mean that it’s draining. I suppose the remedy is to use clay pellets or sponge rock in combo with the power plus?
A. Looks like a nasty case of snow mold. The SAOS cattleya mix is something like 30% clay pellets, 30% coarse Orchiata bark, 30% sponge rock and 10% charcoal. Even so, occasionally you'll get snow mold after several years in the pot and it will smother the roots. Good that you found it, you can just remove all the bark from around the roots and repot.   (Jul-20)
 
 
Repotting Phalaenopsis
Repotting Phalaenopsis

Repotted Phalaenopsis

Q. Is the stem of this orchid rotting? If not, should I put it into the medium? A couple of spikes are growing, but she dropped two leaves last few days. I repotted her about 2 to 3 weeks ago after I noticed that one of the leaves was turning yellow and the sphagnum moss was turning black. If the stem is rotting, I wonder if I should cut portion of the stem and/or spikes to save this orchid. Please advise.
A. Phalaenopsis are monopodial, which means that they grow up on a vertical stem, getting new leaves at the top and losing leaves at the bottom. With the new leaves and stem, come new roots growing from the new stem. With the losing leaves at the bottom, the stem becomes woody and the bottom stem and roots ultimately die. Some repot phals every year, some every 2nd or 3rd year, depending on the condition of the potting mix and how far out of the pot the plant has grown.
  If it were my plant, I would get some root stimulator, some long fibered New Zealand sphagnum moss and an empty pot. Cut the stem below the last aerial root and also cut the two flower spikes off. Spray the stem and the roots with the root stimulator. Then, wrap the stem with some good sphagnum moss, and drop the plant into the pot, placing an inch or two of styrofoam peanuts at the bottom and leave the rest of the aerial roots open to the air in the pot. You can mist, water the plant every other day or so while you are waiting for new roots to branch from the aerial roots and new roots to form from the upper part of the stem. You can then start backfilling the pot, a handful at a time, with your phal mix of choice.   (Jul-20)