Question
Hi Wayne - I have an oncidium mendenhall that moved with me last May from San Francisco to Seattle. I brought him to the office to stay warm through the winter, but I think the air conditioner tortured him, despite the weekly waterings. The pseudobulbs have shrunken, the leaves look dehydrated, and he hasn't bloomed for months. He used to bloom multiple times back home in San Francisco.

I brought him home from work to check the roots and when I released him from the plastic pot, I found a mass of beige/brown roots tightly wrapped around a wad of moss, not green/purplish like my other orchids. So I trimmed off a lot of the roots, cleaned out the moss and repotted with fresh moss and orchid bark mix. I have been fertilizing once a week with orchid food, every 3rd week with bloom food. Since I've started this regimen, the leaves have started to turn brown, but one of the buds has started turning green. Am I doing the right thing or should I take it in to an orchid nursery? I'm trying not to panic or be overly desperate. Thanks for your help.

Jamie

Answer
Thanks for your question Jamie.  As you may know, Oncidium Mendenhall is a warm growing hybrid that likes a lot of light (It is a Carter and Holmes hybrid from Newberry, South Carolina where there are very hot summers). I know that Washington is known for much cooler and more cloudy conditions than San Francisco.  Most oncidiums grown there are of the cool growing type.
I prefer not to mix moss into the standard fir-bark based orchid potting mix because the moss retains moisture resulting in a potting mix that deteriorates much more quickly.  I recommend that it be potted in a fir bark based potting mix with medium sized particles (ie about 1/2 inch average size.)  Wet the potting mix for at least an hour after removing the finer particles (ie dust and debris).  The soaking helps to make the fir bark more water retentive. It is normal for the pseudobulbs to shrink some during the rest period. Best time to repot is when you see new growth beginning to emerge at the base of old pseudobulbs. It will enjoy being outside in a semishaded condition as long as temperatures remain above 55 degrees F..  With an "open" potting mix, both water and air should flow freely through the pot so the pot should have at least a half dozen drainage holes. Keep the base of the old pseudobulbs even with the top of the potting mix as they will give rise to the new growth.