Wow 87! thats a big difference than the actual air temp. I dont think it would mind if it were summer, but you dont want them to grow at this time of the year because the new growth is always the most tender. I try to keep my plants above freezing, but below 75F which is hard to do with all the up and down temps we have been having (lately its been more down than up) I would try to find a way to give it some air, but at least you know it wont die from cold! Of as you said you can just put it on when temps go below 15F. You said it only increased temps by 5 degrees, did you mean 50?

Good luck, hope you find just the right temperature.

The palms should have survived 87 but as TZ notes that should not happen too much.

Your winterizing is really good, its that your plastic does not have much air space which is OK as long as you keep the lights off on sunny warm days. I made the same mistake today, left the lite on in my tracky enclosure with the sun out and I am sure it was 90*. I had my wife turn it off a few hours ago. I did not realize how warm it was today - 35 is too high in the sun for the lites. The weather report said today was going to be harsh cold and they are off by a crucial 6 or 7 degrees.

Aviod using lites on sunny days over 30, it really has not been that cold. I use my lites only at night usually. I would use them if days are stuck in the teens or 20ish.

Personally, I like the idea of letting my palms experience some cold weather. When I first put them in the ground - the first winter - I really babied them, and each year after I have put less and less protection. This is the 2nd year in the ground for my Pindo, and last year I gave it a lot of heat in an enclosure - this year, it is enclosed but will use quite a bit less heat.

I would love to see my Butia sometime soon!
It's buried/frozen to the ground now so I'll leave it alone.
You can but a Thermocube on line,they(one model)come on at 35(F) and go off at 45(F).A lot less stressful for your palms then winter/summer temps so close together.I put one IN with my Washy,better than coming home on a sunny day to turn off the X-mas light at noon only to find out it's 95(F) in there!

You said it only increased temps by 5 degrees, did you mean 50?

No I meant that without heat just the warmth from the sun heats them up 5- 10 degrees I'll use thermo cubes next year

Oh, i thought you were taking about it with the lights on. Still 5-10 degrees is a pretty good temp increase (might be marginal for a pindo palm if this winter is as cold as its forecasted to be though). Thermo cubes are a great idea, I think I might use them next year too because they are much easier than plugging the lights in everytime it gets cold.