Dendrobium Leaves Yellowing
Q. My dendrobium had seven spikes blooming under a tree this fall. Now all the leaves are yellowing and dropping, why?
A. Many dendrobiums are tolerant of the cold, but not the phalaenopsis type. They don't enjoy temperatures below 55 or 60. If they get colder than that, the leaves will yellow and drop. The good news is that the plant will perk up again in the spring. (Jan-12)

Salt Encrustation on Clay Pots
Q. I bought a lot of used orchid pots and have not been able to remove the salt encrustation, how can I remove the white lime scale from the pots?
A. All pots should be soaked in soapy water and scrubbed to remove roots, potting mix and other detritus and then disinfected by an overnight soak in a mix of bleach (10% bleach or 9 parts water to 1 part bleach) and pool algaecide (2 tsp/gal if 10% strength) followed by a second soak to dissolve the chemicals. An hour bake in the oven at 225 degrees will kill any virus.
- Dishwasher. If the pots still have visible white stains, run them through the dishwasher with twice the normal amount of soap. The heat and soap will draw the salts either out of the pot or to the outside edge of the pot. Try scrubbing any residual salt from the pot.
- Mild Acid Soak. If the pots still have visible white stains, try an overnight soaking in a mild acid. Use white vinegar in whatever concentration you are comfortable handling, either a pure or a diluted (10%, 25% or 50% vinegar) solution. Scrub any residual salt from the pot followed by a second soak to dissolve the acetic acid.
- Nuclear Option. If salt encrustation is still present, consider admitting defeat and replacing the pot because the next alternative is the nuclear option. It involves a concentrated acid soak using muriatic acid, either pure or diluted (10%, 25% or 50% muriatic acid) followed by a fresh water soak to remove the acid from the pot. There are many safety and environmental hazards involved with handling muriatic acid, so be prepared to follow all label precautions, use gloves, goggles, etc. as well as have a disposal plan because the acid is highly corrosive and foams excessively when you try to neutralize it with limestone prior to disposal. Muriatic acid represents a potential threat to you, your pets and your environment that can be avoided by simply replacing the pot. (Jan-12)

Lower Phal Leaves Yellow and Drop
Q. Some of the lower leaves of my phals are yellowing. I know this happens often right after repotting, but these phals were reestablished, so what’s happening?
A. I think that is Collar Rot, or Southern Blight, caused by the fungus Sclerotium. In phals, the base of stem turns light yellow, later dark brown, and the infection spreads to roots and leaves. White fungal growth can sometimes be seen on stems. There is a rapid collapse and rotting of the plant. Isolate it from your other plants, spray the surrounding area and plants with pool algaecide and drench the infected plant with a thiophanate methyl solution (Cleary’s 3336 or Banrot). (Jan-12)

Mealybugs on Paphiopedilum Flower
Q. I have mealybugs on some just in flower paphs. They are all over the flower. (a friend gave me spray with alcohol, water and soap but told me not to spray the flower). Now what?
A. Use a Q-tip dipped in alcohol to delicately kill the mealybugs on the paph flower, and then your friend's concoction can be sprayed on the flower stalk and in all the paph crevices. They must be in between the leaf fans at the base of the plant and crawling up to dine on the delicous flowers, so really spray in between the leaves and in fact drench a little in the mix cause they can hide there too. (Jan-12)

Dendrobium spectabile
Q. I am trying to cope with this huge Den. spectabile. It was repotted last year and though it didn't seem to send out any new roots, it has 5 new shoots on it and I am wondering if I can cut off some of the old canes that look awful. I had it outside most of the summer and the old leaves have brown spots and edges on them (no bugs that I can see) and the new leaves are fine. Will it hurt the plant to cut off some of the old canes? The buds where the blossoms grow out seem to be old and dried up. Any advice?
A. If the leaves look diseased, you can cut them off, but leave the canes as this is where the plant stores energy and water (think of them as humps on a camel). You can remove the canes if they are soft or withered, otherwise leave them on, particularly because this dendrobium will bloom from old as well as new growth. The Den. spectabile blooms in the March time frame. If you've got 5 new leads it should be healthy and happy. Be patient, give it a ton of light and plenty of water and keep your fingers crossed! (Jan-12)