Ezzirah,

Robert took the words right out of my mouth. A couple of things to understand about the pop-up type greenhouses:

(1) the plastic is thin and it likely will be just as cold inside the pop-up at night as it is outside so don't expect it to keep the plants above freezing without putting something inside to serve as a heat source; and

(2) shade will be just about as important in winter as in summer.

The smaller a greenhouse, the harder it is to keep it from getting too hot and too cold and and every day of the year without a heating/cooling system.

Robert prepared me well for learning to manage my own little greenhouse by posting photos for me and explaining things to me and answering my questions several years ago. Without his advice, I am sure I would have made a lot more rookie mistakes with the greenhouse than what I did.

Here's my experience from the first two years:

Year 1: With no shadecloth on the greenhouse, it got as hot as 145 degrees on a sunny winter day even if the outdoor air temperature topped out in the 50s or 60s. This is the famed greenhouse effect. Plants do not care that it is the greenhouse effect. They don't like it. Even if I opened up both doors and all 4 vents, it still could hit 115 degrees on a sunny day, and it could hit 115 by mid-morning. Running a ventilation fan helped a lot.

With no heat source inside, no reflective shade cloth (I'll explain that in a minute) to help hold in heat, and no bubblewrap insulation, the greenhouse got exactly as cold at night as the outside air. My greenhouse is 10' x 24' and got very hot on a winter day and very cold on a winter night. We won't even discuss how it felt on a spring or summer day.

Year 2: We added aluminet shade cloth (50%) which not only kept the greenhouse cooler during the day, but also holds in a couple of degrees of heat at night. This made a huge improvement in the greenhouse both day and night. It brings with it, however, its own challenges. I use the greenhouse to hold seedlings after they leave the light shelf indoors, so they are partially hardened off since they spend weeks under 50% shade cloth, but I still have to eventually move them outside the greenhouse to give them exposure to 100% sunlight so I can harden them off to outdoor conditions. Still, this beats carrying them inside the house every night, up the stairs to the light shelf, etc. and then back outside every morning. Now, I just carry them a few feet outside the greenhouse to set them in full sun. Also, the main thing I wanted it for was wind protection. The strong winter and spring winds just beat seedlings to death when they are being hardened off, so being able to have them in the greenhouse, even with all its doors and vents open and a fan running is still a lot less wind exposure than they would face outdoors. It is important to run that fan in the greenhouse because it gives them "wind exposure" before they go outside into the real wind.

WITH the aluminet shade cloth, on a cold but sunny winter's day, and with all the vents and doors open, the greenhouse might be only 80 degrees if the outside air is 50. With the shadecloth and with doors and vents closed, it still hits 115 degrees by 9 or 10 a.m....and that is a 240 square foot greenhouse. Imagine how quickly heat can build up in a 25 square foot greenhouse. Your greenhosue likely will heat up more quickly than the interior of a car. Before the shade cloth, it could hit 145 degrees by noon on a sunny but cold day if the doors and vents were closed. So, managing the temperature inside your greenhouse involves not just the use of shadecloth but also opening doors and vents and using a fan for ventilation as needed. I can't sleep in late either or the greenhouse will be roasting hot on a cold but sunny morning by 9 or 10 a.m. I try to be outside to open the doors and vents every day right around sunrise if not before.

At night, without a heater or solar collectors or something that helps hold in heat or provide heat, your greenhouse will get just as cold as the outside air. The second year I added 30 or maybe it was 36 molasses feed tubs (each of them the size of a whiskey half-barrel planter) filled with water to serve as solar collectors. We also had about 30 or 40 cat litter buckets filled with water. All the tables for the plants had the solar collectors beneath them. I also had cat litter buckets lining the north wall sitting right on top of the tables to serve as insulation for the plants from the cold north wind, particularly at night.They did a really good job of heating up and holding the heat all night, but it isn't a slam dunk.

On some nights, the solar collectors kept the greenhouse 8-10 degrees warmer than the nighttime low temps. On others, they only kept it 0-2 degrees warmer than the outdoor air. The hotter the daytime temps, the better they kept it warm at night. If it was a cloudy, cold day and they couldn't build up a lot of heat, the greenhouse was cold at night.

To some extent, I could manipulate the heat. For example, on a cold day, I might close the vents and doors (all or some of them) at 2 or 3 p.m. to hold in the heat before the sun got too low in the sky. On a hot winter day with a warmish night expected, I might not close the doors and vents until 4 or 5 p.m.

Also, I am at home all day and can check the thermometer and look at the plants and see if they are too hot or too cold. That's important with our fluctuating weather that can change on a dime.

Having a Min-Max thermometer and looking at it daily is important. It helps you understand how much your greenhouse heats up/cools off, etc.

Many people who buy pop-up greenhouses to raise seedlings or to harden them off fry their plants the first year by not understanding how quickly it gets hot in there, or by underestimating the need for good air ventilation.

Full sun in the winter and spring will kill plants in a heartbeat inside a popup greenhouse that size unless you religiously vent it every day. That is where managing it gets tricky if you work because you aren't at home to open or close doors and vents as needed during the day. I leave my 50% shadecloth on my greenhouse all day every day year-round. Even with shadecloth, vents and doors and a large fan for ventilation, the greenhouse is too hot for plants in May through August. I don't remember now if I moved plants into it last September or not until October, and I still had to have the doors and vents open so they wouldn't roast. You cannot go off for the day without opening doors and vents for ventilation or your plants are likely to be roasted, toasted, baked and broiled when you return.

I would start slow with the greenhouse and would have a back-up plan for everything.

Next winter I am going to heat my greenhouse, at least on the coldest nights, which wasn't part of the original plan. This past winter, with all the solar collectors, there still were nights when we went down into the 20s and the greenhouse dropped down maybe to 28 or 30 instead of 20 or 23 degrees like the outdoor air, but warm-season plants still would freeze at 28-30. Only, of course, mine didn't because I had a very heavyweight row cover over the plants in the greenhouse. Between all the solar collectors and the 10 degrees of protection given by the floating row cover, my plants survived 20 degrees, but I was worried they wouldn't. Next year I'll just buy a heater and stick it in the greenhouse and use it on sub-freezing nights.

Finally, in the winter, you can use your greenhouse to keep warm-season plants warm if you wish, but if that is your choice you cannot also grow lettuce in there at the same time. The heat needed to keep tomatoes happy all winter, for example, can mean the air temps in the greenhouse get hotter than the lettuce will tolerate. When I would close the greenhouse doors and vents in mid-afternoon in December so the greenhouse could build up enough heat to keep the tomatoes happy all night, the lettuce would get too hot, and therefore, the lettuce in the greenhouse bolted in mid-winter whereas the winter lettuce in the ground in the garden and in the cattle trough planter survived all winter and lasted until April or May, depending on where it was growing. If I waited and didn't close the doors and vents until it was almost sunset, the nights in the greenhouse were great for the lettuce but too cold for the tomato plants.

I would not attempt to keep anything in a greenhouse in full sun in winter. It just gets too hot. Want a sauna? That's what a greenhouse gives you on a sunny winter day...a toasty hot, humid sauna.

Dawn