Question
I have 400 various cymbidiums in various sized pots, outside under a 40% shade cloth shelter.  Live in a summer rainfall area. The plants were all very healthy with lots of spikes forming. I follow a feeding programme and water when necessary. At the beginning of winter (April) we had two nights of black frost - although I cover the whole shelter with frost cover - I found that a lot of the plants were affected by the frost.  During October, when I repot and sort out all the problems (although I check all my plants monthly) I discovered a lot of the bulbs were either petrified and dried out, or mushy.  I cut out all the damaged bulbs, but now I find that I am still loosing bulbs.  What do I look for now and what should I have done after the black frost?

Answer
Hello Pam,

I'm sorry to hear about the weather problem you had this past winter.  I had a similar experience in 1990 when the daytime high temperature during a 2 week cold spell was 26F or -4C.  Although I had covered all of my cymbidiums (almost 1,000), I lost over 80% of them.  I was not the only one though as there were horror stories from almost all orchid growers and was the hot topic at every club meeting for months.  Since that year, there have been many ideas bandied about on what to do the next time.  Here are some suggestion you can try.  

Fully cover them, string christmas tree lights in and around the pots and turn them on.  The lights generate a little warmth and the hope is that that is enough to prevent freezing.  I've tried this and it worked pretty good, only lost a few leaves that were in contact with the plastic cover.  

Install sprinklers over the growing area and when temperatures are forecast to be below 0C, turn them on.  The thought here is that water freezes at 0C and it prevents the plants from being exposed to any lower temperatures.  Have not tried this one but a commercial grower swears it works.  

There is a product called Freeze Cloth that is supposed to keep plants under it 2 to 3C warmer than the air temperature above it.  Of course, if temperatures go much below -5C, the cloth is marginally effective to prevent damage.  Have not used this product but many local growers do.  

Frost normally comes down vertically so having some overhead protection can prevent it from falling upon the leaves.  This does not keep cold temperatures out, only the frost.  My growing area has a semi-solid cover over it.  

Now, back to your quandry about what to do with the ongoing bulb loss.  As I said, I had a similar experience and had done what you have been doing to try and save them.  After several months of working to save them, I threw away a lot of plants that had already lost many bulbs and only had one or two left with no leaves on them.  I decided it was a better use of my time and effort to work on saving the ones that had the least amount of damage and thus the best chance for survival.  As you sort through your collection and repotting them to check their roots (you will find most of them have dead roots), look for any indication of new growth at the base of the bulbs.  To see if there are growth eyes still alive, remove all dead leaf remnants from the bulb then check around the base to see if an eye is present, but if the eye is black the eye is probably dead.  If there is no growth eye evident, the chances that it will make a new growth are minimal.  

I hope your cyms survive better than mine did.  Of course, with the space left open by dead cyms only means you need to get new ones to fill that space.  (grin)  

As for what you can do the next time black frost is in the forecast, you can put the frost cover up and try stringing christmas tree lights amongst the pots.  You can also try a radiant heater (the type that contains oil and shaped like old-time heaters) under the cover with fans to circulate the heated air.  

I hope this has helped give you some ideas you can try in the future.  Think about them and whether one will work for you.  

Jim Kawasaki
San Jose, Ca.