Choosing a Greenhouse

Image Gallery

Grow food for the table — and the spirit — any time of year

What gardener doesn't dream of having a greenhouse? Dozens of greenhouse kits can be found on the market (see the chart below ), or you can build your own from scratch (see " Building a Hoophouse " ). Either way, you'll have a warm, fragrant place to play and plenty of fresh food and flowers right through the winter.

Prices on greenhouse kits vary widely, depending upon the type of glazing provided. Kits with polyethylene film can cost less than $200, while a kit using much more durable and better-insulating polycarbonate can cost $4,000. Here's what you need to know before you buy or build, including a detailed discussion of various glazing options.

GLAZING

The most expensive component in many greenhouses is the glazing material. The better the glazing, the more expensive the greenhouse. Glazing permits the entry of light and solar heat into the structure. An array of choices exists for glazing, including glass, vinyl, fiberglass, polycarbonate, acrylic and polyethylene. The materials vary in cost, ease of application, solar performance and longevity.

Whatever glazing material you buy should be made specifically to withstand the sun over many years without losing clarity. Virtually all plastics eventually break down (they either turn yellow or white and/or become brittle) when exposed to the sun's ultraviolet light, limiting the amount and quality of light that enters the greenhouse. Even so, some plastics are a sensible choice; many are guaranteed for 20 years. Some plastics are many times stronger than glass. Where I live in Wyoming, hail occurs an average of 10 times a year, so glass is not a good choice. For our specific climate and budget, I choose polycarbonate. There are many pros and cons to consider in selecting the right glazing. Often the No. 1 deteminant is budget. Whatever you choose, be sure to read a copy of the warranty or guarantee before you buy.

POLYETHYLENE FILMS

Films are the type of flexible plastic used in plastic bags or food wrap, only much thicker. Brands vary in thickness, quality and lifespan. In general, you get what you pay for. The biggest drawback to polyethylene (or "poly") is that the lifespan usually is between one and six years (depending upon the manufacturer and a little luck). Single-layer films are most common, but commercial growers often set up a system with two layers of polyethylene and inflate an airspace in between (with a small squirrel-cage fan), which provides some insulation. Other, tougher polyethylene options are woven poly and high-density polyethylene, a honeycombed material with better energy efficiency. Some poly films hold in long-wave (infrared) radiation better than others, holding more heat — important in colder climates.