Heat source for greenhouse?

[Southern Gardener]

I have no idea what to use to heat my little greenhouse. We are supposed to get temps in the 20's this week so I think I'd need a little heat at night. Can someone recommend? A small propane heater? Electric? (I'd have to run an extension cord) My dad suggested putting a 250 watt heat lamp - would that work? Any suggestions?

Thanks!

 

[nachoqtpie]

I literally just posted this yesterday in someone elses greenhouse post!

Solar heat! It looks very promising! If you could get your friends and family in on drinking soda/beer/anything in cans you could be in like Flynn! It doesn't look to be overly hard, just a bit time consuming.

 

[digitS']

Joan, I'd like to be of help but I don't know if I can be. One thing: with perennials in there to spend the winter, I don't even cover them unless the outdoor temperature is going below 15F.

When I built a little lean-to greenhouse (I think it was about 5' by 12') against the south wall of my garage at another home, I decided to put small bathroom electric heater in there. I'd guess it was about 1200 watts. Well, the door froze shut!

For a number of days that winter, I could do no more than look thru the glass at my heater running merrily in the greenhouse. So much for making the structure useful! You probably wouldn't have this problem with yours.

You may need to ask yourself what is your intended use for the greenhouse. I don't turn on the natural gas furnace in mine until seedlings for plant starts go out there. There are a dozen or so plants in there now but I'm hoping that they are pretty much in dormancy. My only concern is to not allow the pots & soil to freeze . . . and sometimes, I'm probably not successful. Still, the rosemary plants get thru the winters without anything more than being covered with a quilt on cold nights (& days).

Steve

 

[Southern Gardener]

For a number of days that winter, I could do no more than look thru the glass at my heater running merrily in the greenhouse. So much for making the structure useful! You probably wouldn't have this problem with yours.

LOL!! No, I don't think I'd have that problem Steve. My main purpose for the greenhouse is to winter my potted plants. I've spent a lot of money in the past buying new plants every spring so I'd like to start keeping them alive thru the winter. Now, of course we don't get winters like you, but we get enough to kill like my foxtail fern that is beautiful right now. We have a huge aloe vera plant that was almost done for last year but recovered thank goodness!

I do plan of using it for starting seeds next year - you know, since I have it and all!

 

[lighthawk]

Those solar collectors do a good job however they would probably overheat the greenhouse in the daytime and they do not retain heat overnight.
Some sort of heat sink might be a better alternative. Many people use 2 litre bottles filled with water that warm up during the day and radiate that warmth overnight. Concrete block will also absorb a good deal of heat and radiate it overnight. Especially if painted black. All depends on the square footage you are heating.
I would not advise running an electric heater using an extension cord. They do make small propane heaters for camping that might do the job but be absolutely certain it cannot be tipped over if left unattended. They also use a lot of propane which can get expensive if you run them for extended periods. Keep in mind any heat source other than a passive one could result in a fire hazard. Good luck.

 

[Southern Gardener]

The greenhouse is only 6x8 so I wouldn't think I'd need anything extreme. I'm looking for something quick and simple - so the solar thing is not for me and since it won't heat at night. The extension cord is out. I'd have to run it from my potting shed and it's supposed to rain for the next few days. I've been doing some reading and I think the best solution is a small propane heater.

 

[thistlebloom]

Keeping in mind that I'm only a wannabe greenhouse owner here's my .02. :/ I only know what I've read, but I think Lighthawk is right in suggesting a passive source of heat. You mentioned laying in gravel for the floor and that would help retain heat from sunny days, and also as Steve suggested, covering with blankets or frost blanket would seem to be sufficient for your climate. If Steve keeps his rosemary happy in an unheated greenhouse up here, where sunny winter days are like hens teeth, you should be fine.

But what do I know?

Keep an eye on that aloe, they start looking pretty sickly in anything going below about 50*.

 

[dickiebird]

Keep an eye on that aloe, they start looking pretty sickly in anything going below about 50*.

+1 on the aloe, I'd get it inside before the temp gets anywhere near freezing!!!!

THANX RICH

 

[NwMtGardener]

I put my huge black water barrel inside my greenhouse last spring, it seemed to help hold some heat in overnight. I also thought i read something about someone burning one of those kerosene lanterns inside their greenhouse overnight. Turned down really low. But of course there would be a risk from the flame! Good luck, and let us know how your plants make out, i'll be facing the challenge again in the spring! This past year i was really lucky and we didnt have any really hard freezes after i got my plants out in the greenhouse, but i know it wont be like that every year!

 

[Smiles Jr.]

Here's an idea that I used several years ago with great success. Some automobile service garages use engine and transmission oil, gear lube, and antifreeze that come in 1 gallon black plastic bottles. We've all seen them in various stores. I even found some 2 gallon bottles like that also. These bottles are rectangle shaped and perfect to fill with a 50/50 mix of glycol and water. You may not need the glycol in LA but here in Indiana we get some pretty hard freezes. At first I had a 2 bottle high row across the entire 12 ft. front of my little (12' long x 4' deep x 9 ft. tall) greenhouse at the ground level right up against the interior side of the glass. During any sunny day the liquid would absorb the warmth of the sun and at night it would slowly release the warmth into the greenhouse.

During that same time I was experimenting with soda-can solar collectors. My experimentation, at that time, was limited to making a solar food dehydrator. I used a 24" x 24" x 36" plywood box as my dehydrator enclosure. One day I got the idea to put some of the black bottles inside the empty dehydrator box and I was able to heat the liquid to around 130*F in 12 hours of good sunshine. As soon as the sun dipped below the useful angle I moved the bottles into my greenhouse and put them on the ground under the rack of potted plants.

I also had some "blankets" that I made out of the aluminum covered bubble wrap insulation sheets that I put on the interior of the roof and three sides of the greenhouse. It was a lean-to type three sided glass room added to the southern end of my tool shed. On several occasions I borrowed a temperature recorder from work and monitored the effectiveness of my efforts. I was amazed at how good these things worked. The best results I ever achieved was -1*F outside and 34*F inside one night. If I remember correctly this occurred at 4:00 AM in January of 2004. My typical temperature increase was around 19*F above the outside temperature.

Of course this took a some labor every day to make sure things were set up correctly and while I used the solar dehydrator I had to lug bottles into and out of the greenhouse every morning and every evening. But it was my experiment and my hobby so it was really a labor of love. We had a big storm with high winds a few years after I built the greenhouse and the tool shed fell onto my greenhouse. It's just a pile of rubble out behind the big barn now.

This showed me that a person can make great use of passive solar heat in a greenhouse.