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Posted by spiroan DFW (My Page) on
Tue, Feb 25, 14 at 11:15

Hi everyone,

My wife just sent me the picture of a greenhouse that was on sale, and it got me thinking about something. It is one of those greenhouses that goes up and down relatively easily, and it is not gigantic. However, it might be big enough to simply put over the top of my "plumeria bed" during the winter. Our temperatures got down to the mid-teens once this year, and a few nights in the high teens/low 20s. If I could find an appropriate heater, does anyone think this idea has merit? Does anyone else in this zone or others do anything similar? If it would work, it would sure save me a lot of time taking plants in and out. Thoughts?

Follow-Up Postings:

RE: Greenhouse

If it's big enough and you put in a heater, I don't see why it wouldn't work. It would have to be well staked to keep the wind from carrying it away.

What about your average low's? Would you still have to heat it most nights?

I lost my greenhouse this winter due to a heavy snowfall. Our winter has been colder than usual and I decided to bring my plants inside and not have the expense of heating the GH. So, without heat to melt the snow, the roof ribs cracked, one by one, in the middle of the night. It was a horrible sound. My husband says he can repair it fairly easily.

RE: Greenhouse

Thanks for the response, Moonie. Looks like you are in zone 8, so I imagine our average lows are pretty similar. During December, January, and February, I would say the lows are in the 30's, maybe just above freezing. But we have plenty of days where the low is freezing or below. And we will have a handful of days where the high doesn't get above freezing.

What kind of cost am I likely looking at to heat it, or is that too subjective to estimate?

RE: Greenhouse

  • Posted by mksmth oklahoma 7a (My Page) on
    Wed, Feb 26, 14 at 10:11

Hey spiro.

I am linking a site that has a good calculator for figuring the size of heater you would need to maintain the temps you want based on you greenhouse size, construction and location. It seemed to work good for me. My greenhouse is a 10x12 hoop house with a single layer of 6mil plastic. normally we have a Natural Gas heater to keep it at 55 or more. I have a typical 1500 watt electric heater that is set to come on if the NG cannot keep up or goes out. This last monday night for some reason the Pilot light on the NG heater went out and we didnt know it. The electric came on an was able to maintain 38 degrees while the actual outside temp was 23. In the past I was able to keep a smaller 6x8 Lean to greenhouse at 55 with the same electric heater but it was on the southside of the house protected from the wind.

All my greenhouses have had a solid North wall. You get very little if any benefit of light from having a Transparent north wall. However you do benefit from it blocking any north wind. Around here we can get some brutal wind chills mostly from the north.

anyways I would say in the DFW area you should be able to keep a small 6x8 maybe 8x10 greenhouse where you want it with a good electric heater.

To determine the cost of operating it you need a few numbers
1. the wattage of the heater
2. the amount of time you expect it to operate
3. your cost for electric, take you electric bill and divide by the Kilowatt hours you used. For me it about $0.09 per Kwh

assume my heater runs from sunset to rise which is not actual but highly possible thats about 14 hours give or take.
1500w/1000=1.5Kwh x 14hr= 21Kwh x $0.09=$1.89 per night or about $56 per month. That would be the worst case in my opinion. Of course on cloudy days without help from the sun you could have the heater running also. This is where being on average plans is helpful.

another thing I have done is on really cold nights I have covered the greenhouse with a big tarp or blanket. Just having another layer of something seems to help keep the heat in better.


Here is a link that might be useful: heater calculator

RE: Greenhouse

Thanks, Mike! Great information!

RE: Greenhouse

I use an 8x10 pop up with a 750watt electric heater on low and it keeps the greenhouse temp no lower than 60 degrees when buttoned up. Most of the time i just used a large fan. My low temp never got below 26 this winter. Only problem is condensation even with the fan blowing.

I think the brand of Greenhouse is call "Flower House" and can be bought online. The first one I had was 6x8 and lasted about 6 years before falling apart. This one is 2 years old and seems to be better built.

RE: Greenhouse

Some of my trees are getting too tall for a greenhouse. Do those of you with greenhouses have this problem as well?


RE: Greenhouse

Yes. I have a built on site 2x4 wood frame/Polycarbonate clear panel greenhouse which is 10 feet tall for the "bigs". Some were starting to brush the top rafters so I pulled out the pallets they sat on and used some 2x4s to keep the thin style containers off the concrete during winter. It worked this year but next year it's almost certain to be too short to keep them in a container.

Once they outgrow this they will either be pruned, donated to the local Botanical Gardens, or driven to the coast.

RE: Greenhouse

K, your greenhouse sounds awesome. I am building a new one this summer but it probably wont be quite that tall. Im doing a lean to that will be about 10x20'. I hope to put a few citrus in the ground permanently. My design only has about an 8-9 ceiling but that should be fine for a small tree or 2.


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