I have one of those cheap $20 greenhouse that my friend picked up for me from ocean state job lot. I put my seedlings in there when they’re outside. I was surprised how warm it can get. Today, the sun was shining bright but it was about 40deg. According to a cheap Walmart thermometer, it was 80 inside the greenhouse. Is that accurate? Can the temp differential be that large?

Here’s a picture of the greenhouse:

I did put the thermometer in the "shade" of one of the pots so it did not get direct sunlight.

i have a couple of those and use them and have been surprised how hot and humid they get. The only problem i had was that if i was caught out with some high winds they would blow over, hence doing what you have done and putting some heavy slabs at the base. I also forgot to water some plants in them a few years ago and it is sur[rising how quick they can dry out.

I don't have experience with the specific type of greenhouse you are using. However I do have a cold frame and 40F above ambient happens frequently in my cold frame--hence the need for it to be self-opening. It looks like your thermometer is in the shade of the pot, that was the one thing I was going to mention, but looks like you've got that part covered. So I'd believe it you're that warm.

In my cold frame I use 1/2 gallon milk jugs, spray painted black, filled with water, to absorb sun during the day and release the heat at night, which helps keep it warmer, especially if I put my insulated cover I made on the cold frame in the evening. They don't do much when we get a 2-3 day stretch of cloudy weather--but that's usually not a huge problem except if I have cool season things and it happens to gets very cold, which usually is only an issue in March.

[mention]jmsieglaff[/mention] glad you mentioned that. Thought about some kind of water radiator before, absorbing heat during the day. interesting your experience with containers.

jmsieglaff wrote: ↑Fri Feb 26, 2021 2:31 pm However I do have a cold frame and 40F above ambient happens frequently in my cold frame--hence the need for it to be self-opening.

Would love to see a picture of the cold frame you have. I would like to build one myself to put up against my house.

I also have a small hoop house for one of my raised beds. I guess I will need to start opening it up soon. I'm trying to find some remote sensors that will work outside so I can keep better track of the temperature. I just ordered a few Aqara temp sensors to try out. I already use them but only inside the house.

ponyexpress wrote: ↑Fri Feb 26, 2021 2:38 pm Would love to see a picture of the cold frame you have. I would like to build one myself to put up against my house.

I also have a small hoop house for one of my raised beds. I guess I will need to start opening it up soon. I'm trying to find some remote sensors that will work outside so I can keep better track of the temperature. I just ordered a few Aqara temp sensors to try out. I already use them but only inside the house.

I'll look to see if I have an old picture I can post, otherwise I'll share one when I get mine out in a couple of weeks. It is a polycarbonate/aluminum cold frame that auto-vents, I purchased it probably 7-8 years ago and it continues to work well. It is very light, so I anchor it with some bricks on both sides. I put it on my deck, up against the house with southern exposure.

Here is the cold frame with some peppers and tomatoes in it from a few years back. I don't put it directly on the deck, it is on a piece of that pink house insulating foam board that I have covered in a gray tarp since UV will degrade the polystyrene. I also made a cover or "shell" for the cold frame, made from the same polystyrene, also covered with a tarp. When I first got the cold frame I did some experiments on night temperatures, with and without the cover, the cover was very helpful, with full sunshine the day before (warm water in the jugs starting out the night), the cover kept it 10-15F warmer than without. I put it on in the evening and take it off in the morning before work. I use the cover in early/mid spring and only as needed, depending what I've got in the cold frame and the weather.

50 degrees above outside is normal for me in zone 6 about this time of year. The more greenhouses I built, the less I wanted one that seals up perfectly, otherwise you can end up with a solar cooker.

Agree that temperature extremes are the norm. I use water containers as well to moderate temperature but it really isn't enough. You need a lot of mass for that to work perfectly, so you will still get a tight greenhouse turning into a cooker when the sun is on.

The smaller the greenhouse the bigger the difference. This will generally lead to tough skins among other things. In the summer some kind of shade cloth is really needed.

mama_lor wrote: ↑Mon Mar 01, 2021 2:40 am The smaller the greenhouse the bigger the difference. This will generally lead to tough skins among other things. In the summer some kind of shade cloth is really needed.

In my case, I’m only using it during the colder months and will put it into storage. I plan to take my hoop house off during the summer as well.

That’s interesting that using a green house can lead to tough skins.

I have this one, I was also surprised at how warm it gets. It got to 50 outside yesterday and this thing started creeping up over 80. I went out and opened one of the windows and it hovered around 75 after that.