Jordan, there are lots of ways to make a less-than-perfect greenhouse better. Charlie and I have had our share of funky greenhouses that we really had to work on! Greenhouses are expensive, but any greenhouse is better than no greenhouse, and with a little work, you can make any greenhouse air-tight.
Getting the side walls to reach the bottom and have excess plastic that folds down onto the ground is really important. This is the quickest and easiest, low-tech way to do that:
Get a roll of greenhouse tape ("Poly Patch Tape" usually 4" wide)and greenhouse plastic ("Poly Cover"), or even bubble wrap - anything will work. If you can't find it at a local store, you can get it online at
www.charleysgreenhouse.com . More expensive greenhouse coverings last longer, but anything will work for one winter if you are on a budget.
Lay the plastic all around the outside bottom of the greenhouse, with the top half up on the walls and the bottom half folded outside on the ground all around the greenhouse - an L shape all along the bottom of the greenhouse.
Tape the top of the plastic to the greenhouse wall in a solid line that leaves no gaps.
Then put something heavy (bricks, cinder blocks, heavy boards, or anything heavy!) on top of the plastic, right up against the greenhouse wall. Make sure the plastic is weighted down all along the bottom, around the corners, everywhere.
Use that same greenhouse tape to patch any holes anywhere else in the greenhouse. Patch all holes tightly. Holes are inevitable! We all get them all the time. Patching holes is a frequent job for greenhouse owners.
Once you get your greenhouse airtight, add a little fan to your propane heater to force some circulation and blow the warm air all around the greenhouse. It will help keep all the plants uniformly warmer. Try to put it up high if you can, on a top shelf or hanging from the ceiling, and blowing from one end of the greenhouse into the center of the room.
If you want to go all out and make a super greenhouse, buy clear bubbled greenhouse plastic, and cover your whole greenhouse with it. The bubbled plastic gives the effect of double-walling your greenhouse, and it will really make a difference with keeping drafts out. Make sure you use enough to fold down onto the ground all around the outside of the greenhouse, and weight it down with something heavy all around. Also seal up every seam completely with greenhouse tape. This costs quite a lot more, so you may not want to do it this year, but for future years you might want to consider it.
You don't need a "perfect" greenhouse to keep hibiscus happy. A little bit of extra work will make any greenhouse better, and any shelter is better than being outside and exposed to very cold weather. Even an unheated greenhouse will cool down more slowly than the outside air at night and heat up more quickly when the sun comes up in the morning. So even a funky greenhouse is better than anything you can do outside, like freeze cloth and Christmas lights.
I hope this helps!
Cindy
