Greenhouse Heating and Cooling

Hey all!
Finally took the plunge and built a greenhouse this year. It’s and 8’ x 12’, 10mil double wall. The temperature regulation of said structure has me a little concerned though. We have it on the north side of our house, hopefully to mitigate too much heat up from the sun in winter, but it’s still running 20 degrees above ambient temperature when the sun is up. I’m concerned about it getting too warm in winter. We usually have a long winter run near 0 F where I’m located (Green Bay), but the temp can swing into the upper 30’s depending on the year. Finding a gas heater with an actual thermostat has been impossible.
Will it be enough to run a fan and open the doors and vents on the warmer days? Any suggestions for a small heater with a programmable/digital thermostat?
Need some advice from the folks that have been there.

I have used this setup for years with your size greenhouse and my trees do really well. I keep it set at around 30 degrees all winter and even when it gets up to 20 below, it maintains that temp. For the heating issue, especially in November till it really gets cold, you will want to cover it with shade cloth. I have mine attached to the internal roof panels year round and during the winter I add an additional shade cloth to the outside all winter. My greenhouse faces south, so I get sun all day during the winter. I have even double wrapped the shade cloth to keep it cooler at the start of winter.
From looking at your setup, you could easily attach shade cloth in sections to the inside of your greenhouse. I live in Omaha, so the temps you are describing are about the same for here. You probably get a lot of wind like we do, to cut the wind down going through the greenhouse, I use the tape below by weather king and seal all of the sections of the panels on the outside. Wind is your worst enemy during the winter.

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I agree with covering with shade cloth - it seems to help with both keeping it cooler in the sun and warmer in the cold, particularly since it helps keep snow on top.

I use the Inkbird ITC-608T since it can handle 1800W and I use a 1500W heater with built in fan. I also set the the upper temperature to turn on a vent fan in one wall. I have a propane heater with 3 settings, but no temperature control that I can fire up when it gets really cold, but I only used it once last year.

My greenhouse is a temporary structure that I take down every year. The plastic was starting to degrade so I am recovering each of the panels. This year they will be covered with a layer of bubble wrap and then 6 mil (0.006" = 0.15 mm) clear plastic. The bubbles on the bubble wrap will face the plastic. I used the bubble wrap on the inside of the frames last year after I put up the structure and it made a big difference.



Here’s an interesting thought. Do you think we ‘molly coddle’ our trees too much?
I for one do not put any of my trees under any sort of protection during the winter. We often get snow, frosts can last for days on end (often at -5 C) and we have enough rain to fill a reservoir, yet my trees all come through it fine and healthy. I have trees of all varieties and sizes from 3ft right down to 2 inches. If a tree survived the last ice age such as a coastal redwood, that tells my they are frost hardy and adaptable so even they remain outside.
I often think that by putting them in shelter they don’t harden up and actually become more susceptible to disease during the growing season. Some trees I’ve have for over twenty years.
I understand the problem in areas of severe cold but I for one like to see my trees

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We very well may, but then again -5c is much warmer than about half of our winter here.
Last year I did minimal winter protection- mulched all of my trees in on the ground with wind protection and lost all but 2 of my mame sized trees, and almost lost a pretty valuable black pine (mulch froze so hard that the water couldn’t drain from the pot when I did water). The big guys faired much better. I just decided I’m sick of worrying about them every year, and chiseling a black pine out of frozen mulch to get it into the garage is something I never want to do again (it pulled through after 80% of the needles going brown).


I don’t baby my trees In the winter. Cinder block enclosure, leaf insulation, tarp over the top when it hits 20F. Good down to -20F…? Very SELDOME lose a tree.
I have lost more trees due to summer heat; and voles moving into the ‘comfortable’ winter storage and eating 48 decideous trees… Put out mouse killer in covered containers!
I took a large JBP into the garage and killed it…along with my favorite mame horse chestnut. Freezedried…
Snow and ice IS an insulator… my trees do much better frozen in leaves.
Do a Mirai search for winter storage. Tons of ideas.


I have very similar winter conditions and storage practice. My big trees are uncovered but out of the wind and direct sun.

I am considering building a small greenhouse for post-repotting, however. It’s those late freezes and nasty spring winds that end up killing trees for me.

In Omaha,
This is the Month where the greenhouse is worth the money for my trees!

Same here. It’s been great so far this winter- with shade cloth, a tarp, and two fans it’s stayed cool enough- and the heater has kept it warm enough. A godsend.

@APG and @TerryBryan — if not too big a hassle would love to see pics of your greenhouses. Contemplating for fall/winter. Thanks…

This is what it looked like before I started pulling trees out. Had a great first winter.

This is right after we finished the full assembly. It’s been a real game changer.

Thank you Aaron! I appreciate both pics! Especially the base. With local ordinance I’d need to do same wooden base vs. concrete.