That's exactly why I bought a small greenhouse this year for my plumies and other tropicals. Even though we don't get freezing temps during day, we still have very close to freezing temps at night. So I guess it is a good investment. I recently placed a Vick vaporizer inside the GH because it was very dry there, and some of the plumies started pushing more leaves. I mainly got the GH for my first-year seedlings, to keep them from going dormant, and because I don't really have enough room for them in the house.
Here's a part of the GH in november, before all the plants went in due to freezing temperatures at night. I also got a double tarp in top of it to keep the warmth inside. And of course, a small heater.
