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Green House Buyer’s Guide

By: Eric Vinje Published: 28 Aug, 15 Updated: 5 May, 18

What frame and coverings to consider when buying a greenhouse kit.

Gardeners view green houses as a dream or a necessity, the latter by those who already have them, the former by those who wish they did. A greenhouse serves many functions and grants many advantages. It’s a place to give seedlings a jump start ahead of the growing season, a place to raise plants, including everything from tomatoes to lemons, that won’t find the growing season they require outdoors. It’s a place to overwinter potted plants and extend the vegetable harvest well past the first (and second, and third) frost. A green house can add immensely to your enjoyment of gardening and its rewards.

Specialized kits make owning a greenhouse easy. But what’s the right setup for you? It’s important to consider what you intend to do in your green house and then make sure you have the room and features those intentions require. If you’re just planning to start some seedling for transplant or to harden off some starts before they’re transplanted in the garden, you might consider a cold frame. But if your intent is to utilize your green house for any of the other uses above — or a combination of multiple uses — a green house is your best and most efficient option.

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Once you’ve decided what you’ll be doing in your green house, consider how much space you’ll need. Make sure you’ll have the room inside the house for all you intend to do. Draw a to-scale floor plan of your greenhouse space using graph paper and find a place for potting benches, grow shelves, and places for large permanent residents, whether in pots or directly in the ground. Then add on a few more square feet. Out growing a green house after only a season or two is a common story among gardeners. Starting with a little more room than you think you’ll need allows for your ambition to grow. More room most often pays for itself.

The next considerations concern which materials are best for your greenhouse’s frame and glazing. It’s important to consider weight and durability of the materials for each and which are best suited to your climate conditions and needs.

Do you want something lightweight that you can move to places in your garden where you want to extend the growing season, spring or fall? Do you need a glazing capable of withstanding the possibility of hail storms or resistant to deterioration from sunlight? Should the glazing be designed to insulate and conserve the cold-season heat generated by the sun? Will your frame be required to support winter snow loads without bending or collapsing?

Here are some tips to guide you in choosing both frames and glazing.

Frame Materials

Wood is often the choice of do-it-yourselfers because of its availability and the ease with which it can be worked. Wood is also strong enough to support what ever glazing you might choose. Overtime, wood, unlike steel, aluminum or plastic, can be susceptible to rot. But with yearly attention and good drainage, wood can last a lifetime. Wood frames are heavy, providing good anchorage. Once assembled, a wood frame also allows for hooks and other attachments for shelves and hanging baskets. Many gardeners think wood is the most aesthetically pleasing of green house frame materials.
Aluminum frames are durable, rust-proof, and relatively light weight. The pieces are often grooved or channeled to allow for easy placement of the glazing. They’re an especially good choice for a first green house.Considerations:Aluminum frames conduct heat. They’ll be hotter in the summer and give up warmth more quickly in the winter. Because of their light weight, some aluminum frame green houses are attached to a steel frame at ground level.
Plastic framing is a good, inexpensive, and lightweight choice that’s best for small green houses. It’s often covered in types of plastic film that diffuse light effectively inside. Plastic frames do not conduct as much heat as metal frames. Because of their light-weight, they’re often anchored on a steel frame. Inside tray supports and hanging racks are often steel-reinforced to increase the weight they can support.
Steel is the heaviest of green house frame materials and is most frequently used for large, permanent, commercial structures. Because of its weight and difficulty to work with (including setting glazing), steel frames can be difficult to maintain.

Glazing

Glass has aesthetic as well as historical appeal as a green house glazing. Tempered glass has taken a big bite out of the breakage problem, but glass is still heavy and expensive to replace. Un-tempered glass will eventually show wear and discoloring. Tempered glass will not. The thicker the glass — green house glazing is often 3 or 4 millimeter thick–the more damage resistant it becomes. Still, winter storms and freezes can take their toll with breaks and cracks of tempered glass as well. Glass, unless treated or covered with special film, does not diffuse light to the plants beneath it.
Polycarbonate frequently replaces glass in small back yard green houses. Despite its lightness, it’s strong and durable. Polycarbonate panels are translucent, not transparent. letting in the kind of soft, diffused light that is most effective in green houses. They come in double and even triple-walled types to increase heat retention. Triple-walled polycarbonate makes for better insulated green houses but doesn’t allow as much light in as double-walled types.
Polyethylene sheeting is the least expensive glazing for green houses. It works well for small backyard greenhouses constructed of plastic frames. It’s also used to cover large and long, steel-framed commercial green houses used to grow tomatoes, corn, cucumbers, and other heat-loving vegetables that need plenty of room. Polyethylene is particularly subject to fading and yellowing and even under the best conditions must be replaced in three to five years. It’s also subject to tearing due to stretching caused by temperature extremes, winds, and snow loads. Among the three glazings listed, polyethylene allows the least amount of usable light into the green house.

Many of the so-called “accessories” that green house kits come with are crucial to the success of your inside gardening. Venting hot air up and out of the green house can mean the difference between vigorous, sun-drenched plants and wilted, heat-struck plants that probably won’t survive the temperatures. How large a door will you need? Does it need to be wide enough to accept your garden cart? Will your growing shelves be freestanding or will they need support from the frame? Will you need a fan to move air in the winter to prevent freezing and when it’s hot to pull it outside? Will you need a heater?

Again, these things depend on your needs and conditions. Making wise choices will be rewarded with wonderful growing.