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!
Sediment Grains on Wooden Basket
Q. Do you know what could be producing the sediment looking grains you see in the picture? I have found them in and around the roots of a few of my more established mounted plants. I went after them with the hose but saw they reappeared after a couple of weeks.
A. That looks like frass from dry wood termites. Take a hose and water blast all the loose stuff away and look for little pinholes in the wood, they are the holes the termites make to push the frass out.
There are plenty of chemicals to kill termites, but the strength recommended for termites is at least 20 times stronger than that which is recommended for orchids. For example, the 21.4% imidacloprid product is used at a rate of about 0.5 mL/gal for orchids and 8 to 16 mL/gal for treating foundations for termites. Perhaps a better plan is to pretreat wooden mounts/baskets for termites prior to use. Alternatively, try soaking the mounts in a strong imidacloprid solution for an hour.
Dark Spots on Cattleya Leaf
Q. This cattleya hybrid has some dark spots but it seems to be just a discoloration? They are flat, part of the leaf, you can’t feel anything to the touch. It does not seem to hurt the plant.
Any idea what it is?
A. That looks like some bacterial blighting that occurred as the leaf was forming. I'm guessing water was cupped by the papery sheath around the emerging leaves and bacteria attacked the soft new leaf tissue. You can try to gently pull down the sheathing so water can drain freely to prevent it from happening in the future.
Was Dendrobium Overwatered?
Q. I repotted. this Dendrobium about a year ago. Someone commented that Dendrobiums like a lot of water, so I watered it often. This past spring it appeared to have developed a new cane with little green leaves at the base which shriveled and disappeared.
On one of the remaining viable canes there are two keikis which looked robust when they first appeared maybe a couple of months ago that are now turning brown.
Have I killed this plant by over watering?
A. Perhaps. When they told you Dendrobiums like lots of water, they should have also told you they like to be potted in extremely small pots. The canes grow so closely together, they can happily grow in a seemingly too small pot for many years. So, if you had used a small pot with maybe an inch or so to grow new canes, you could have watered it a lot and still the roots would have had enough air around them to grow happily. It was the combination of a too large pot and the copious watering that may have done your dendrobium in. Whether the keikis were a normal growth pattern or perhaps the plant's last gasp at survival is anyone's guess. It is quite possible the keikis were trying to grow even though the main plant was doomed. I am guessing that had the plant been potted in a pot half the size it was, it would still be growing happily today.