If I supply bottom heat to plants how cold can the air get?

Question

This is my first year with a hoop house. I live in north Texas (Zone 7b). I have a few tropical hibiscus and what not in big pots that I don’t want to bring in. I keep a lidless crockpot full of water going, which makes the air nice and moist. I have a heat lamp and a rigged waterbed heater for bottom heat. I just hate to chance it and find out out my hoophouse wasn’t warm enough. Thanks so much!

Answer 1

It is hard to say how cold it can get. Any part of a plant will die if it gets too cold. So with your hibiscus, bottom heat may keep the roots alive, but the leaves and branches above will die if the air gets too cold, no matter how well you heat the roots. The roots will survive and the plant can regrow from them, but this is not likely what you want.

That being said, it sounds like you are supplying more than just bottom heat, and this is good. If you can keep the whole hoophouse warm, then you don't need to worry about roots vs canopy. Get a thermometer and keep an eye on the air temperature. Keep the air temp above what your plants can tolerate (this will vary from plant variety to plant variety).

Also be sure that you don't go in the opposite direction and accidentally cook the roots by applying too much heat to the roots. You just need a gentle heat on them.