Hi Michael, great question. the temperatures around my wall drop into the 50s at night in January and February. Patrick Blanc (the inventor of the green wall) has built a number of green walls outside. He has several on the outside of his house in Paris, France and the temperatures drop below freezing in winter. If your wall on a South facing wall, it will be a couple of degrees warmer than the outside temperatures. Also, the fact that you have it attached to the house will keep it warmer as well. I think most orchids will actually overwinter better than most other things. I would stick to intermediate species as they could tolerate lower winter temperatures, and warmer summer temperatures as well. The general rule of thumb is that the colder the temperatures the drier it should be. Also, you could put a heating cable under the felt and turn it in when temps drop below optimal growing temperatures. You’d just have to make sure you don’t staple through it by accident.
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