Carnivorous Plants/over-wintering container-grown Sarracenia
I have a question regarding over-wintering container-grown Sarracenia. I live in zone 6a and the night time temperatures can drop below 20 degrees F. I realize that Sarracenia are frost tolerant, but prolonged freezes can damage them. If I were to winterize them, what do you think would be the best method to use? Even if I were to put them in an unheated garage or greenhouse, don't you think temperatures below 20 degrees F would still be harmful to them for sustained periods of time?
It really depends how cold, and how long. If you only have a week of low 20's or teens the garage is going to be just fine. If it's really cold (I did experience single digits in St. Louis one time), put them in the garage and cover them. Be sure to spray them with fungicide before storage. Cut off any dead or dying foliage. I've had all Sarracenia species survive a week of temperatures in the teens here in the Northwest with tarps over them. It's important that they are on the ground and not up on a table or bench. The ground gives additional warmth. We have usually only lost plants when they've been up on benches, or out exposed alone. During this time their pools freeze solid.
If you think you are looking at more than a week, then you might consider a little heat to get the temperatures at least in the upper 20's. This usually isn't too hard in a greenhouse or garage.
Much of this is going to depend on what will best work for you. Any kind of cold frame is going to be better than plants being fully exposed. You can also group them together next your your house, mulch them, then put a tarp over them.
As long as they are not allowed to be exposed and dry, they tend to be able to handle quite a bit of cold. We have customers in Michigan and Upstate New York with bog gardens that mulch and cover them each year, and do fine.
Here's a few plants to give a bit more protection to. Flytraps can be more sensitive, D. trayci and F. filiformis "Florida Giant" is not very hardy along with Pinguicula primulifora. Sarracenia psittacina is often reported to be less hardy, but we've had no problems with them. Certain S. leucophylla clones can be tender such as "Titan". S. leucophylla "Tarnok" is quite tough, and can handle low temperatures.
On the other side these plants can take very cold temperatures: S. purpurea subsp. purpurea, S. oreophila, S. rubra subsp. jonesii, Carolina forms of S. flava, S. purpurea var. montana and most of the North American sundews not mentioned above. Hybrids of any of these are quite tough too.
Hope this helps.