Building a Cheap Greenhouse

Mother Earth News | May 12, 2014 | homegrown.org

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I can’t believe I haven’t written about our greenhouse. We’ve been using it for at least a year and a half now, and I’ve been oddly silent about it. I guess it’s probably because it’s not 100 percent complete. We have one small area that still needs a permanent covering, the windows need new glazing, and it is in desperate need of new paint. But it’s still functional and gets a lot of use. And it only cost us about $300.

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That might sound like a lot of money until you consider that this greenhouse is 8 by 12 feet and uses glass glazing. Buying a glass greenhouse that size will generally run you around $5,000.

Why Choose a Glass Greenhouse? 

Why a glass greenhouse? Why not just make a hoop house to save money? Hoop houses are great, don’t get me wrong, but they just don’t stand the test of time. While they are cheaper to make upfront, there are some concerns you have to take into consideration. The material usually used for hoop houses is plastic sheeting, which doesn’t last more than a few years, even if it is UV-resistant greenhouse plastic film. I’d prefer not to have to add more plastic to the landfill or spend the money replacing it. Also, you have to give special consideration to the hoop structure. PVC pipe will degrade the plastic through chemical reaction faster than it normally would degrade (and most isn’t UV resistant), so you either have to wrap the pipe or use another material, like galvanized pipe, which increases the cost. Plus, we have a very windy site for most of the year, and plastic sheeting just wouldn’t hold up.

Polycarbonate greenhouses also degrade from UV but last substantially longer than poly film. Polycarbonate is a plastic, and even though it may hold up for 10 to 20 years when properly treated with UV stabilizers, it will discolor and become more opaque after time. It also becomes brittle. Double-walled polycarbonate adds the benefit of being more insulating than both glass and film. It can be quite pricey, though. Not as expensive as buying glass specifically for a greenhouse, but if you can do glass, which is superior to both film and polycarbonate, for less than either, why wouldn’t you?

Sourcing Free Windows and Materials

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 It’s all about the windows. It is amazing how many people are trying to offload free windows. Craigslist is where we scored the majority of ours. We also scored a free door, which was half-window, from my best friend, who had just bought a house and wanted to replace her front door. We stockpiled old windows until we had what we felt was enough to begin building. Before starting, we laid out the panes on the ground so we could get the right configuration to fit the walls of the greenhouse. Do this carefully. We had a few casualties but fortunately had enough windows to make up the difference. We also made sure that we had some windows with frames so we could open them as needed when it got hot in the summer.

Next, we had to figure out where to site the greenhouse. We had a space on the north edge of our property that wasn’t shaded, and it wouldn’t shade out anything. We made the long 12-foot wall south facing to maximize sun exposure. We also decided that, since the north wall is facing a fence, we could just use plywood for it. We framed up the structure with new lumber, which is where a good portion of the money we spent went. The most costly part of this job, however, was the roofing material. We used some of the extra pavers we had on hand to level the structure, since our ground slopes. It was also imperative that we add extra bracing, as the weight of the windows can be quite substantial.

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The biggest score from our window search were these two 6-foot-long windows that someone had purchased and never bothered using. They easily spanned the whole lower half of our south-facing wall. It was a tight fit, but we got them in. From our next-door neighbor, we also got narrower windows that flank the door (seen in the first photo).

Once we got most of the windows in on the south-facing wall, we started framing the door and getting the roof joists up. Sexy, ain’t it? We decided to do a simple sloped roof rather than a gable so that the south side would get even more sun exposure, especially in the winter, when the sun angle is lower and when we need the greenhouse the most. One note: A door that comes with a jamb will make framing much easier.

Once the door was in, we were able to finish up adding windows and roofing. For that, we used clear corrugated plastic sheeting. It’s not a particularly pretty greenhouse and it does need a coat of paint, but it’s definitely functional.

Greenhouse Interiors and Greenhouse Floors

Of course, you also have to think about the interior. Where are you going to put plants? And what about the floor? We scored some pea gravel off of Freecycle, enough to put down a nice 3-inch layer. We put down weed cloth first, though, so we won’t be fighting the never-ending onslaught of bindweed and Bermuda grass inside. Tom build a fantastic 8-foot-long potting bench out of scrap wood, and we bought some heavy duty utility baker’s racks for the plants. We’ll probably switch the locations of these, putting the potting bench on the east-facing wall and the racks on the south-facing wall, so we can add another rack. We’re also using an old compost bin (our chickens do all of our composting now) as soil storage.

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Have you built your own cheap greenhouse out of scavenged materials? Do you have photos or tips to share? Post them below!

This post originally appeared on HOMEGROWN.org.

Rachel’s friends in college used to call her a Renaissance woman. She was always doing something crafty, creative, or utilitarian. She still is. Instead of arts and crafts, her focus these days has been farming as much of her urban quarter-acre as humanly possible. Along with her husband, she runs Dog Island Farm, in the San Francisco Bay Area. They raise chickens, goats, rabbits, dogs, cats, and a kid. They’re always keeping busy. If Rachel isn’t out in the yard, she’s in the kitchen making something from scratch. Homemade always tastes better!