Orchid Culture - 2022 Questions & Answers
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!
Paph Flower Rotting
Q. I suspect a crown rot and not a bud. What would you advise? They have now been put closer to the fan so the centers dry out quicker. They were on the ground underneath my orchids and I think it stayed too damp.
A. That is the emerging flower bud. If the bud is rotting, I would suspect dew/condensation settled in the fan and rotted the bulb. If that's the case, you can remove it and pour some fresh hydrogen peroxide into the fan, draining away the water after 15 minutes or so. If the bud is not rotting, rejoice, cause that is a beautiful multifloral paph!
Q. Can vase sponges be used as an orchid pot? Do they require desalination prior to use?
A. Did you get those sponges from Tarpon Springs? They are harvested from salt water, and then processed which involves a lot of rinsing. I just tested one of mine by running some water through it and it wasn't particularly salty. I'd soak it good before using it, changing the water a few times. I wonder how long it will last without breaking down, let me know!
Q. I purchased this antelope type dendrobium that was originally mounted upside down on a board. Is this a dendrobium that goes dormant? I can’t seem to make it happy.
A. The spatulata type dendrobiums grow pretty much like cattleyas. If you took it off its mount and put it in a pot, you probably compromised the root system which basically doesn't like to be disturbed. They grow well in pots, usually pots much smaller than you think they need because the canes grow so closely together. A good dendrobium potting mix is one with not too much organic material because organic material breaks down after a couple years, and then it must be replaced with fresh material, so you disturb those roots again. Keep it a little drier during the winter season until new roots are ready to grow in the spring, and then think about putting it into a smaller pot with a coarse potting mix.
Q. I am in a panic mode. I lost my Vanda tessellata 3 weeks ago to what appeared to have been a sudden bacterial infection that spread like fire in a few days. This morning my very healthy Gongora atropurpurea is covered with what appears to be bacterial infection. I discovered the problem on 4 more stanhopeas, all in the immediate vicinity of the Gongora. All 5 plants are very good plants and I am disheartened but hopeful that trimming and spraying will allow them to come back. I also keep them dry for now and isolated.
A. I don't think that is rot from the cold weather per se, I'd guess the damage was caused by cold water dripping onto the leaves and causing the localized cell collapse followed by a bacterial infection. With this cold weather, water can readily condense and drip on the leaves. Wet plus cold is a deadly combination. I think your instincts are correct, trimming away the bacterial infection will help stop it from spreading and copper sprays should be protective of the remaining leaves. I'm guessing your well established plants will throw off a bumper crop of new unblemished leaves soon.
Reddish Leaf Markings on Cattleya
Q. My first concern is the wine colored marks that have appeared on the newest growth of my Cattleya (Laelia) purpurata. Should I be concerned?
A. My first thought when I saw that wine colored discoloration on the new leaf was the possibility that it was a sign of virus, in particular Odontoglossum Ringspot Virus. I asked for a picture of the flower, because ORSV often is reflected in color break in the flower. The flower could just be exhibiting a suffusion of color in the petals, or it could be color break because the markings are more distinct on one petal than the other, and color break is assymetrical. Jan ordered some test strips, and alas, it tested positive for ORSV.
Red Rhizome Ring
Q. On repotting an epidendrum recently, I noticed this half circle of red on the rhizome.
Is this red ring always fusarium fungus, even in an otherwise healthy plant?
If I can’t prune it away and it appears to be through out the whole rhizome, do I need to throw the plant out? Can it be treated?
A. It sure looks like fusarium, but perhaps it hasn't totally invaded the vascular system in that the entire rhizome doesn't look affected. I would sterilize between cuts, and keep cutting until you don't see the red ring. The pseudobulbs don't look compromised/dehydrated like they would from a fusarium wilt. I don't know if you can cure fusarium as opposed to prevent it from spreading/infecting new tissue, but a highly rated chemical would be one containing the active ingredient pyraclostrobin like Pageant or Empress Intrinsic.
Catasetum Growth Beginning
Q. Is it time to start re-watering when I see signs of growth?
A. No, it's time to repot, if it needs repotting. Whether you repot it or not, do not water until the plant is about 5 inches tall and the leaves have unfurled. Otherwise you will likely get crown rot in the tender new growth.
Q. I have 4 small catasetums all of which have basically no leaves but a few spikes. Should I be watering them or leave them dry to be dormant? It’s been so warm, don’t know if they’re confused or this is normal.
A. I'm guessing that catasetinae is really a Mormodia, which is a hybrid between a Mormodes and a Clowesia. The small flowered Clowesia are winter bloomers from leafless bulbs, very floriferous. You don't need to water them unless you feel like the bulbs are shriveling up. If you feel compelled to give it some water, you can place it in a saucer and let it wick up moisture from the bottom.
Yellow Pseudobulb on Nobile Den
Q. I bought some Dendrobium Nobile orchids a few weeks back and one of them now has a yellow and soft pseudobulb. I water them once a week so I'm not sure if I over watered them or not. Should I remove the pseudobulb or let it remain there?
A. I'm sure you have read about the nobile dendrobiums and how they like a coolish, dryish winter rest. The nobile pseudobulbs are much softer than those on other dendrobiums, but they should not be yellow. That means they are beginning to rot. If it starts to blacken or get mushy, cut it off. You probably shouldn't be watering it once a week, particularly with it being in sphagnum moss. You should let the moss dry entirely before watering until after growth begins in the spring.
Oxalis in Orchid Pots
Q. I decided to try the Bonide Chickweed, Clover and Oxalis weed killer. It did a pretty good job. The sprayer it comes with is not that
great and it seems like you need to get good coverage on the leaves for it to
So I tried a fine mist sprayer from RePotMe.com and it worked much better
Thus far, I have not seen any negative effects on the orchids.
A. That's great information. I had to buy from EBay because the local stores didn't carry it and Amazon wouldn't ship to my location. I'll try that on the oxalis growing around my stanhopeas, they have resisted everything I've sprayed on them. April update:
I tried some on some stanhopeas that had a persistent case of oxalis, and ended up losing some leaves so I can't recommend it on the thin leaved orchids. I'll continue using products with the active ingredient Diuron, it just may require more than one application.
Dendrobium Needs Repotting
Q. This dendrobium has really grown. It has been in this pot for the past three years and is growing out of the pot. How should I repot it and how much bigger the pot should be?
A. You may consider just dropping it into a larger pot. If it is currently potted in bark, you might want to jet out all the bark you can by turning the plant and pot upside down and spraying the media with a hand nozzle set to jet. Then just drop it into a larger pot and let the roots grow into and around the new pot.
Phalaenopsis Leaf Blemish
Q. I'm having an issue and can't seem to identify problem. It seems to be moving throughout the plant.
A. I think that is one of the Cercosporoid fungi. You can see a pentagonal blotching in the leaf discoloration. It is really pervasive in dendrobiums. You'll have to remove the damaged leaves to remove the source of inoculum from your growing area. I suspect the cooler nights we've been having caused condensation on the leaves which helps the fungus develop. More air movement, less leaf wetness and spraying during danger periods helps. Daconil and Pageant are highly rated for it, you can use Thiomyl or Banrot in a pinch.