I have designed and built several greenhouses for myself. No matter where I have lived, temperature control has always been an issue at some time during the season. Here are some solutions that I have found work.
To keep a greenhouse warmer during the fall I put as many as I think I need milk cartons filled with water around the interior base so they can release their heat into the evening. You can also use many other types of water containers. The bigger the better. I also try to build my greenhouses with the bases buried in the ground as much as possible.
To keep a greenhouse cooler I have put vents at the bottom around the inside perimeter and panels that open up top. I use piano hinges, long rods, etc to build and control them. I also am a believer in white wash as a way to decrease the amount of heat entering the greenhouse. Paint as much of the outside as you need to. I will easily wash off and will not contaminate the soil.
Finally, there are any number of inexpensive solar powered fans available to move the air inside and or exhaust it the outside, which is absolutely necessary in any climate.

Hi Thomfoote, I've built my own greenhouse as well. I absolutely love going out there on a chilly winter day and putter about. I use plastic jugs as well to retain the day's heat, but I wrap mine in black trash bags. The water inside heats up twice as fast and hotter than the unwrapped ones. I also constructed a small wooden compost container inside the greenhouse. This also generates a bit of heat for those cold winter nights. I'll take a couple of pictures tomorrow and post them.

aphrodite891 said: I absolutely love going out there on a chilly winter day and putter about.

Me, too! It's in the low teens here, but sunny, so I'll be doing some puttering around with seeds out there today.

aphrodite891 said:
I also constructed a small wooden compost container inside the greenhouse. This also generates a bit of heat for those cold winter nights.

Luv the smell of nearly finished compost while I'm out there working.

Which zones/areas are you in?

Thomfoote,

I meant to mention that I'd been casting about for a method of shading .....thanks for your suggestion of whitewashing!

Thanks for the information on using milk jugs! I just popped over here to see if I could find a good thing to do during the winter, to try and keep my greenhouse a little warmer, without having to use a heater. Even a few degrees would help. I've had nights where it's a degree or two colder inside there than it is outside!

I use fans to ventilate my greenhouse. It serves as a double purpose for me. It releases hot air out of the greenhouse and increases the cool air inside. It is ideal to place plants 5-6 feet high in front of vents to draw air through plants. Thanks for the tips about milk jugs. I am now thinking of placing them in my greenhouse but first I need to find where to get those jugs . - P.Jefferson

Another tip... most of the cold air comes into the greenhouse at ground level. If you build up a low wall of wood or straw bales or other insulation (outside or in) it will help. My greenhouse stays about 10 degrees warmer than outdoors.

A friend spreads a layer of chicken manure and covers it with mulch (dirt floor of course). The manure generates sufficient heat for his wifes' tropical plants. I daresay she doesn't putter in there though. lol

pjefferson, I don't know where you live, but in the US, they are the plastic containers that milk is sold in at every grocery store. They have a handle too, which makes them easy to carry.

We're getting ready to move out of state, so I decided not to put my greenhouse up this winter. I would have loved to have kept some plants in there, but it would have been too tempting to start some seeds too. I'm not good with that kind of temptation! So, I'll have to wait until next winter to try out the milk jugs for myself!

Covered buckets or barrels would also work, especially if the sun hits them directly. They'll absorb the most heat, and release it quickest, if painted black.

But you should cover them or the warm water will tend to evaporate, waste the heat, and re-condense on everything.

The New Alchemy Institute on Cape Cod (I think it was them) suggested a double row of black 55-gallon drums along the North wall. They used big fish tanks with tilapia in some greenhouses.

Someone else suggested a row of discarded floorboard radiators (copper pipes with fins) along the ceiling to collect heat, and a pump to push the warmed water down into big PVC pipes under a concrete floor.

(Or run an electric heater for 5 minutes every 30 minutes during the coldest hours.)

Still in progress of building an 18' X 24' hoop house. I have used gallon water jugs around tomato plants for years, to keep nighttime temps up so fruit will set. I put the jug inside of a 5 gallon pail with the bottom cut out, then plant the tomato in the middle. I get earlier planting, as this contraption will protect tomatoes down to 25 degrees or so, if it gets colder than that, I will cover the container with row cover. By the time the tomatoes are above the bucket, danger of frost has passed. This will be the first year all of my tomatoes are in a greenhouse/hoophouse. I do not have heat for it, but do have raised beds and do plan to use some water storage around plants as well as row cover to extend the season. Once I get the skin on (sometime this next week, it arrived today), then I will monitor temps high and low compared to high and low outside in our mountainous zone 6.

Have already started seeds in the house, once they sprout i move them to a small attached greenhouse, and put them inside a portable greenhouse. I set the plants in trays on top of light cables,. Then have water jugs in the bottom of the portable, for heat storage. I do put a small heater in this greenhouse, to keep night time temps up until it warms enough in the spring.

Great looking house , will be watching the progress,
I bet those seedlings are wanting outside about now

How's your greenhouse holding the heat? I found that having the heater on the floor and fans high that it holds the heat by several ºC. The fans make a huge difference. My GH is 8'X12" Costco kit. I have a infrared electric furnace with the little electric heater 3000BTU working off two different breakers. With -13ºC, I can keep the greenhouse above 10ºC. In past years I had lined the greenhouse with bubble wrap, but it is a lot of work and fairly pricey. The bubble wrap also changes the light conditions. This cold spell will not end too soon. Cold & sunny is ok, but these cold cloudy/snowy days suck.
-13ºC=8.6ºF and 10ºC=50ºF

I agree we could use some sunny days . In the sun my house is 85+ by 10:30 am but without the sun burrr
I don't heat my small house but will start some seeds last of the month so it needs to stay above freezing.

First thing this morning it was around 27 degrees outdoors, but with the compost cooking in my 10x12 unit, it was 40 degrees in there. That's sufficient overnight temps for me. The only sprouts I have in there so far are some sedum, but I'll be looking out for new arrivals within days, most likely. As long as we don't go below 20 anymore I should be in good shape. The sun is out a bit right now, so I have a big fan running and it's a lovely 70 degrees inside.
I'm hoping to spend an hour or two out there today.

We've been using a quartz heater on the nights it dips below freezing. Fairly economical since we haven't had too many or too cold of nights.

We actually have water cooler jugs and milk bottles filled with water also. Daytime temps have been in the 80s and 90s. I haven't set up a fan yet because I have a door at each end (10x20 size gh) and we have had a lot of wind so there's actually been a lot of circulation in there. I like the idea of a compost in there but I'm too stingy to give up my space for it!

There are wide shelves above the compost bin, starting at waist-high, so I'm really only losing a bit of floor space. I realized after the first year that all I needed to do was dig a pit for it so that it would be low enough to build the handy shelves above it.



Joanne,
Your GH is ever-so neat and tidy...I love it!

Oh, that's a good idea, that changes things! And I have access to HOT horse manure!!! Wow, next year may be a different story.

Yes, Joanne, your GH is very neat and tidy. I had to move into mine as soon as they got it up, without even being able to put down a floor so all I have so far is cardboard. I'm probably going to do mulch, unless there's a reason not to? The one at my son's has pea gravel under the shelves and bricks in middle and open ground for planting on the end. I do have open ground for planting, but don't have patience to put in the framing and bricks and sand, etc...I'm not a fan of pea gravel, too hard to walk on.

I'm using hot horse and barnyard fowl...in moderation. The year I tried adding blood meal was a very odoriferous affair!

I have a mulch floor over dirt. I like it just fine.

Yay for the mulch floor then cause I can get the mulch FREE!!! And yay for the hot horse. I am going to do that for next year for sure!!!

Yeah, I'll bet the blood meal was a nose tickler!

Thanks. I have to do my winter sowing yet, so once the storage area of the jugs is free, I will move some of the plants down to make room for the tomatoes.

I would like to mention a very cool set up that I seen last week. I'm helping out at a specialty grower and was so impressed with her propagation house. She has water bladders on the tables (like a waterbed). Under the bladders are copper water pipes that have hot water from a water heater (temp controlled). It keeps the soil a perfect temp for propagation and the air temp a bit cooler. Years ago she had used actual water bed bladders, but now there are options out there for different industries and she buys the bladder material by the roll and cuts it to size. There is a special glue and each bladder has a fill valve. The trays sort of float on top the bladders.