Greenhouses: what are they and how do they work?

It's getting to be that tail end of winter where I'm impatient for the snow to melt and the trees to grow leaves so we can enjoy some greenery again up North! If you also live somewhere chilly, you might be interested to learn more about ways gardeners can extend their growing season such as greenhouse techniques.

Cilantro sprouting from seed bringing a bit of green to my snowy world!

Greenhouses can be small or large and be made using glass or plastic, but they have the same basic goal: to create a controlled, moist, warm environment ideal for growing plants. The primary transparent material lets in sunlight and creates a barrier to keep heat and moisture from escaping. We might imagine a greenhouse as a large, permanent building such as a plant nursery or botanical garden, but home gardeners can have smaller versions based on their needs. For indoor use, you can purchase seeding trays with plastic greenhouse lids for starting plants indoors while there's still a frost risk. You can even DIY one using plastic wrap -- I tried it and saw condensation and warmer temperatures under the plastic almost right away! 

Making the most of the Northern winter sun to create nice warm soil for seed germination. The white condensation on the plastic shows the DIY "greenhouse" at work trapping moisture!

Outdoors, home gardeners can use plastic tunnels (also called hoop houses when large) or boxes known as "cold frames" to extend their growing season. These are structures that shelter an area of soil to create a warmer-than-natural greenhouse environment while still being outdoors. These techniques might not be greenhouses in the traditional sense, but they use the same principle in a temporary way or a smaller scale to protect plants and seedlings from the elements. 

Inside a high tunnel at Penn State's research farm	Low tunnels (photo via wikimedia commons)	Cold frame image from Iowa State Extension

Do you extend your growing season by seeding indoors and/or in a greenhouse? Let us know in the comments if this article gave you any new ideas to try out this year!