CYMBIDIUMS THAT HAVE BROWN PSEUDOBULBS
Brown pseudobulbs can mean a variety of things; one, the media is going bad. Two; you are overwatering, three; there is too much acid in your water, four you could be under watering, five it has an illness.
I found for my area, the water was not helping my cymbidiums. I noticed after every watering, one or two of the cymbidiums would have yellow leaves and start dropping them and within a week, they appeared to be dying. I added a little baking soda to the water, 1/2 tablespoon to 1/2 gallon. My cymbidiums seemed to love this and the next few days, I saw new growth on many of them.
If you repot with new media when the cymbidium is not in bloom, that will be fine. Just remember not to put into a much larger pot, or the cymbidium will work on more roots and not blooms. If your cymbidium is crowded in the old pot, give it about a 1/2 inch more around the pot. This will cause the roots to spread out a little and still bloom later in the year.
Overwatering and under watering is different for each area in the U.S. You have to find your own method. I would suggest taking one of your cymbidiums for a tester. Water, normally and check in four days putting your finger all the way to the bottom of the pot or lifting carefully the cymbidium out to see if it is still wet or damp. If not, you can water again lightly. The only way to know is to test.
There is such a thing as black rot, University of Minnesota recommends these things: How to Fix Orchid Root Rot
Before Pruning Water Thoroughly. ...
Remove the Orchid From its Pot. ...
Remove Excess Planting Material. ...
Prune Damaged Roots. ...
Spray the Roots with Fungicide (Optional) ...
Repot with Fresh Material. ...
Allow the Orchid to Recover.
Lastly, fertilizing is important too: The American Orchid Society says: “Fertilize at the proper time to help Cymbidiums flower. Use a high nitrogen fertilizer such as (30-10-10) from March until May, a balanced fertilizer such as (20-10-20 / 10-10-10) from June until September, and a blossom booster such as Dyna Grow Bloom (3-12-6) once you see spikes forming in early spring.”
