How warm can I make my Patio Greenhouse?

I have a greenhouse similar to (perhaps exactly the same as) the one pictured. What sort of temperature can I expect this thing to hold over the outside air temp both through the day and night time retention?
My ideas already for heat retention include:
I can use southern exposure.
Next to my brick house.
I will build a brick platform for it to rest on.
I have thought of placing approx. 6 little Gerber 2oz. food jars on each shelf, which will contain water. Perhaps one or two 2 liter bottles of water on the bottom shelf.

I'm in zone 7, NC. and would like to get an idea of what to expect from this thing through the winter here.

If all else fails I suppose I could run an extension cord to a ceramic heat bulb placed in the unit, but I'd like to avoid the need for electricity if possible. Ideally I'd like to have nighttime drops no lower than 45F.

Anyone used these and have input?

This message was edited Oct 31, 2008 6:16 PM

I have one of these that I use from around the first of March through the middle of May for tomato plants. During that period of time I can tell you that this little greenhouse can get darned hot in the daytime. Cooking hot. I usually end up in the mornings unzipping it and taking clothespins or those black office clips and clipping the unzipped door either totally open or open enough to let the heat escape especially up at the top. I don't know about night temps because I'm too chicken to take a chance on my tomato plants getting bitten and I don't heat it.

Janet

The insulating properties of that thin plastic are not very good, if you have nights that get below freezing I don't think there's any way it'll be 45 inside there without a heater. And since the insulating properties are poor, a heater is going to be pretty inefficient and if you have very cold weather then I'm not even sure if the heater will be able to keep it at 45. Those type of greenhouses are great for getting a jump on starting things in the spring, but for overwintering things that need to be kept warm they are not very good.

Maybe you can place the unit over a basement window and force massive amounts of cellar air up into it, but I agree with ecrane3 ..... it's so small and the plastic so thin, it will be next to impossible to keep warm.

Of course, you have to have a basement with windows to do that (Plus, you should probably have bars on that window). I think if you try to heat that with electricity, it will cost a small fortune, and you would still lose anything tender.

My two-story, 320 sq. ft. greenhouse (not the cold frame) is built right off the house, and uses the basement windows as a forced air heat source for the winter, which works quite well in my situation.

Do you have any alternatives to keeping plants outdoors all winter in your small cold frame? I am in zone 6a and my cold frame, which I built out off a plywood base with old recycled house windows and a poly roof, is attached directly to the garage (southern exposure) but I only get to use is seasonally, like Janet. (see photo)

A nother problem with that little green house is that when you do use heat in it moister forms on the walls big time. You could get better results building a cube of pvc pipe and heavy plastic and use the christmas twinkle lights.

I know people who swear by small Christmas lights, not the LEDs. They put them around the base of a plant or wrap them around the plants, then cover them. Maybe you could intertwine the lights around the plants. It's worth a try.

Ahhh, thank you all for your help. Unfortunately I do not have a basement so that option is null. I do have an abundance of Christmas lights in the attic but no power source outside. I can run a power cord out there but it will need to pass through a window or door frame and I'd like to avoid heat loss in my main house.

I have two, 1.5'x4' shelves (inside) with HO-T5 grow lights above them that I use but I'm already out of room there. Bringing plants inside isn't much of an option because the wifey hates them in the house.

Perhaps I can upgrade the existing plastic liner with bubble wrap or an additional shell wrapped around it. What kind of generic plastic can I use for a makeshift greenhouse? I don't have a greenhouse supply store near and doubt that shipping in real *mil poly for this itty bitty greenhouse is worth it.

Home depot or Lowe's or any hardware store has plastic that will do. Will cut down on some of the light.

It might help to understand what you're trying to grow out there--do your plants really need to be kept at 45? I don't think you're ever going to keep things at 45 in there on cold nights unless you have a heater, and your heating will be much more efficient if you have a GH made with the twinwall polycarbonate (rigid plastic, not sheets). But depending on what you're growing, you may not need things to be that warm, some things might be fine if you can just keep them from getting cold wind and keep them a few degrees above the outdoor temperatures.

Hoyas!

Perhaps I will just try to find some of the twin wall poly around town and build a lean-to type shelter on the south side of an existing shed.

"If you're gonna do something... do it right... the first time!" I heard that a million times growing up...

OK, they probably do need to stay warmer. You'll still need a heater with the twinwall, but at least that provides better insulation so you'll probably be able to keep the temperature where you want it. I don't know how much space you have, but if you've got a bit of room you might consider a Harbor Freight greenhouse--they have a couple different sizes and the prices are VERY affordable compared to other GH's made with the twinwall polycarbonate. When you look at the price difference it seems like one of those too good to be true things, but they are for real and their GH's seem to be just as good as ones that you'd pay twice as much for. http://search.harborfreight.com/cpisearch/web/search.do?keyword=greenhouse&Submit=Go

We used clear commercial grade plastic shower curtains around our hut and swingset frame. We also did our patio canopy last year. It averaged approx. 10 degrees higher than the outside temps....everything lived. During the day I would open them up and let them air out. It's inexpensive and works for the warmer zones that do get below 50 during the nights. We had about four freezes and everything made it.

I've also done the thin plastic here around a covered patio and it worked fine to keep things from freezing but in colder zones you need more than that--a 10 degree difference from outside temps in zone 7 isn't going to keep tropicals from freezing.

True.....it only works in warmer climates. The tropicals are tender. Most don't like it below 50. We can get down to 28 for four hours, so at least the ten degrees keeps them above freezing. If your nightly temps are are in the teens or lower twenties, 10 degrees probably isn't going to help. You will need a heater.
Tropicman lives in Kansas and has lots of tropicals. He would be one who could help! You could read his previous threads. He has loads of info on overwintering.

I'd say throw a big blanket over the top of the thing at night, to retain heat, and put a light bulb or heat lamp in there or one of those small ceramic heaters for heat at night too. If you want to get really fancy, tack together an old comforter with some bubble wrap or reflectix on the inside.
You can get a pre-wired plug through thermostat that you can plug other things into from farmtek--it's a little bit expensive, but you can use it for other things later on too. Anyway, then you can set your temps the way you want it.

http://www.farmtek.com/farm/supplies/ProductDisplay?catalogId=10052&storeId=10001&langId=-1&division=FarmTek&productId=50304