Eight Important Factors You Must Control If You're Gardening in a Greenhouse
The important things to consider.
Light levels.
There are a lot of folks who think that just because you stop a plant from freezing by putting it into a hobby greenhouse, it will keep growing through the winter.
I know more than one gardener who wanted to grow tomatoes year-round (it can be done) and thought a greenhouse would do the trick. Here's the trick.
In low light months (November through February) there simply isn't enough light outside to keep plants growing and fruiting. They'll all slow down no matter how much heat you toss at them. If you want greenhouse vegetables to keep on growing strongly, you have to give them adequate light levels.
The problem with this of course is that the harvest amounts aren't going to be very high (you can never get enough light onto these high-light need plants) and it becomes uneconomical to grow them.
Vegetables
So while you can't economically grow greenhouse tomatoes, you can grow a lot of leafy vegetables such as spinach, lettuce etc and you'll never want for salad fixings.
I had a big bed in the middle of the greenhouse (2 cement blocks high filled with an soilless mix - Promix) in which I grew all kinds of vegetables that thrived in lower light conditions (mostly leaf vegetables)
Containers
The major issue with my greenhouse growing was that I didn't want to have to run the greenhouses in the summer time - the energy costs to keep them cool are substantial. So I tended to grow everything in containers in order to move the plants out of the greenhouses after frost.
I used clay pots for the most part and found the plants did very well in them.
Propagation
The serious advantage to gardening in a greenhouse is that you can propagate darn near all your plants so your costs are reduced to near zero.
This is particularly true for those of us who collected "different" annuals and kept them over from year to year.
Simple propagation systems worked well to produce scads of cuttings for container gardening and great garden flowers.
Water
You really want to have a source of water so you don't have to bucket it to your plants. I have to tell you that carrying a bucket gets really old, quickly.
I ran 3/4 inch plastic hose underground to the greenhouses and it worked quite nicely.
Ventilation
I mentioned this above but too many people don't calculate exactly how much air they have to move out of the greenhouse in the heat of the summer.
Here's how to do that
Remember that plants stop growing (photosynthesis stops) around a leaf temperature of 83F. Temperatures over that (as in a hot greenhouse) are merely stunting your plants.
Construction
I dealt with this in other areas but generally, a decent sized greenhouse is fairly inexpensive to build out of 2x4's.
The place you don't want to skimp is in the plastic. There's nothing like watching your plastic get too brittle in winter and shatter into a gabillion bits in a high wind - knowing all that work you did with the plants is now gone. (been there)
Summary
I'm a big fan of gardening in a greenhouse - but do take a few minutes to consider the facilities and what you can grow in them before you rush out. But then rush out. :-)
Doug's solar greenhouse in spring circa 1979
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