first year for my new 6 x 8 Harborfreight greenhouse and we even calked all the seams. Raced around today putting all the plants inside because it's going down to 44 tonight. It's 54 out right now at 2 AM in the morning. The greenhouse is the same temp. I expected at least a few degrees warmer. I know I can bubblewrap the sides etc but I expected the calking to help. I'm very surprised. Not sure if I throw those emergency mylar blankets over the plants maybe that will provide a few degrees? I plan to use lightbulbs or a small heater later but that may be like heating the great outdoors given my experience tonight.

If I bubblewrap it does the sun still warm it during the day? And what thickness of bubblewrap is best?

I've never used the bubblewrap so will let someone else speak to that issue, but my greenhouse (a Rion, with twin-wall poly), if not heated, will also be essentially the same temp as outside at night; once it's light out, though, it warms up much more quickly (even on a very cloudy/rainy day). And when the temperature drops outside it takes somewhat longer for the temp in the GH to drop. Although I never used the mylar blankets, I don't actually think they will keep the plants warmer at night, but possibly would provide frost protection; I usually use some 'floating row cover' if I'm worried the temperature is going too low. Or, if your plants are on (or planted in) the ground, covering them with the blankets would probably hold in some of the ground heat.

My two 10'x12' GH's are wrapped in 16 mil solar-blanket material and it is guaranteed to last for 10 years. The nice thing about solar-blanket material is that it allows (diffused) light to pass through along with infrared (heat), insulates (some) against cold penetration, but I made to hold the heat in. I still have to use two heaters in each GH though. We got down to 33 F this AM and are supposed to get down to 28F tomorrow AM.

In my experience greenhouses are cold when you need warmth, and too hot in the summer. They can be improved if you are willing to jump through hoops, AND spend a lot of extra money. My main gripe about them is that they DON'T work as is, so I consider it consumer fraud.

I had to wrap my GH (8x16) in a solar pool cover to help keep the heat in. That helped a lot, too. Where do you get solar blanket material, Ken?
I use one of those oil-filled heaters; they seem to be less expensive to operate and have worked quite well for me. If the outside temps don't get too low, it will maintain an indoor temp a little over 15 degrees warmer than outdoors. Of course, I also use seedling heat mats when I'm starting seeds; much easier to keep the flats warm than the whole GH.

I ordered my first two rolls from "In The Swim" but went on eBay/Amazon for my second roll. There are lots of sources of solar blanket material and you can (perhaps) find a better deal going online. I also used this material to build a temporary GH along one wall in my garage. It is approximately 6'x10'x8' H and that's where I am over-wintering my potted plumeria (20) and cuttings (75) and some mounted staghorn ferns. I have one of those oil-filled heaters and "fired" it up last night when the temperature dropped to 31 F. I had the heater set at the lowest temperature and it kept the GH a toasty 75 F. I am going to replace that heater with a 4' base-panel heater, one that I can further reduce the heat output. I could not believe that oil-filled heater kept that space so warm. I just want to keep the temperature around 60 F for those plumeria.

I also have one of those oil-filled heaters in our new addition. There is an in-wall heater, but the oil--filled one (and on the lowest setting, too) does a much better job! As you say, almost TOO good.
I'll have to look around for the rolls of solar blanketing. There is one section that could use a bit more insulation.

Thank you for all the comments. Appreciate it. By morning my greenhouse was actually 6 degrees warmer than outside temp so I was feeling happier. Also realized our outside thermometer is on a brick wall that warms all day long so it takes it longer to drop temperature. That probably explains why it took until very late for the GH to register a bit warmer than the outside temp. It did warm up very quickly to 85 In the GH today which was nice since it took it all day to get to 69 outside.

Tonight I have a 65 watt bulb in there and loosely wrapped the mylar blankets to see if any warmth bounces off them onto the plants. It will be even colder tonight at 42 so will see how it does. Kind of looks like a space ship all lighted up in the dark. I will have to work up something better before winter freezes. Also discovered we have a bunch of old fashioned Chrisrmas lights. Will be interesting to experiment with those too. Want to see what makes the most difference before we are hit by an actual frost. Will keep eyes open for one of those solar blankets.

Thanks again for all the comments.

Drdawg do you put the blanket on the outside or inside? Either way seems like it would be challenging getting it on.

Did you use any weather stripping? I find the Harbor Freight GH to be leaky. I caulked the windows in as well, but thought that was supposed to help hold them in rather than keep cold out. I am putting in door seal on the doors tomorrow. The blog recommends using a rope-like foam insulation on the crown. I plan to also put some above the windows. I also use heaters. See the Harbor Freight Greenhouse thread in the Greenhouse Forum.

Looking at the stats I recorded:

Friday night
Low temp outside 44
Low GH temp 47

Saturday loosely wrapped plants in GH with mylar blankets and put 65 watt light close to floor:
Low temp outside 42
Low temp in GH 53

Shady green thumb: We calked and used the weatherstripping that came with the door but nothing else. Ours is the harbor freight. Cheap end of the scale but fun for starting out.

See my post above--The mylar blanket and incandescent light worked very well. We are putting some "grommets" that we got at Home Depot (sold in section where you find shade fabric) in the mylar and will figure an easier way to do a better drapping than last night. Got ten Mylar blankets at Amazon for less than ten dollars. It's pretty tough but can tear (but can also be taped if torn). I hear they sell a tougher version designed for outside use too. Will be interesting to see as it gets colder whether we need another light. We calculated a 65 watt bulb running 8 hours to be less than a dime so very affordable. Putting the bulb in a holder close to the floor allowed the heat to rise up through the plants. Didn't run a fan to circulate heat but may try that also.

Wow, looks like the mylar blanket and light bulb worked pretty well!
I think the worst outdoor temps we've had to deal with here, at least since we got the GH was around -15. That time I had to use a propane heater overnight, but that was before we got the oil-filled heaters. That night was a bit of a challenge! But that was the year I got carried away trying to start things too early--heh, January is NOT a good idea here. (I only use my GH for seed starting in the spring, not for overwintering.)
I put the solar blanket material on the outside of my GH, but I was able to nail it down permanently because my GH is wood framed. I've looked at those Harbor Freight GH's and I'm not sure what would be the best way to attach the material to them. Ken?

http://www.rei.com/product/407...

Here is a blanket that might be ideal. Heavier weight and long lasting i would think and already has grommets!, $17 at REI but 7.80 at Walmart online. Out of stock at wmart but put in email for notification.

Ecscuba said:Shady green thumb: We calked and used the weatherstripping that came with the door but nothing else. Ours is the harbor freight. Cheap end of the scale but fun for starting out.

Ours is a Harbor Freight, too, @Escuba, and I am totally pleased. Mine is the 10 x 12. I won't be changing out anytime soon. I expect this one to hold up well for a long time. With the added enhancements from the HFBlog, it is as good or better in some cases than the more expensive ones. You should see the heat system shadytake/Melissa and her husband put in. You will be as jealous as the rest of us. Go to the end of this thread to see her photos as well as other ideas others have done to their project:
The thread "Harbor Freight Greenhouse projects" in Greenhouses forum

Escuba, definitely check out the modifications that Dave, Shadygreenthumb and Shadytrake made to their HF greenhouses! (there may actually be others on that thread that I forgot about, if so, sorry!)

So far I am pleased with my HFGH except I wish I had gone 8 x 10 instead of 6 x 8. It's kinda crowded in there already. Today I planted seeds in long containers - lettuce, arugula, misoto rose radishes (can't wait for these), regular radishes, and Anaheim chili peppers. The plants I moved I moved in there already have lemons and mammoth jalapeños. Lots of herbs. Three large tomatoe plants in bloom.

Been running the fan in there a bit as it seems like it might be good for the plants.

Am planning to add some raised bed planting area along the south side of the GH building with cement blocks, and "lids" with corrugated polycarbonate panels attached to PVP pipe. I figure I can grow a lot of spinach, lettuce, and other winter crops this way and get 8 feet long of planting space down that side.

Husband built me a potting bench with cement blocks and a chunk of granite that was left over from kitchen counters when we built the house. That is SOOOO nice. He used that cement "glue" in tubes from Home Depot so no cement work involved. HD buckets hold organic soil.

I am sure an amature at all this but it was so much fun planting and being outside today.

I appreciate this forum and everybody sharing their ideas.

That is a pretty cool potting bench!

Seriously awesome potting bench!!

My mind keeps reading your user name as "Escanaba," which is the town I live near...

WEEDWHACKER That's funny. I see you are in Michigan. I am a transplant from Farmington Hills, Michigan, near Detroit. U B cold this time of year!