Garden Greenhouses

So, what are your choices when it comes to getting yourself a greenhouse? First, consider your limitations.

The greenhouse site absolutely must have the best exposure to sunlight that you can provide. A greenhouse without sun is no use at all. Ideally, you want it exposed to sun all year (especially spring and fall) and all day, but if that's not possible you must do the best you can. Your possible sites may be against the house (in which case you might do best with a lean to greenhouse) or away from the house, where you'll need to build a freestanding greenhouse.

Your budget controls a great deal of what you can do. A rigid-glazing (glass or plastic) greenhouse on a concrete or brick foundation, with heating and supplemental lighting for the winter, is indeed expensive to build and to run, but there are ways to bring down the cost:

• Build with used windows, single or double paned


• Use an existing foundation from a shed or garage


• Build with used bricks or concrete blocks


• Insulate and use double glass to cut running costs

Lower down the cost scale is a lean-to greenhouse, rigid glazed on a foundation, which uses part of the house structure and connects to the house's electrical and heating systems.

Next come greenhouses built with flexible sheet glazing material such as polythene, which comes in a range of weights and qualities from light, cheap stuff which shreds in the first season, to heavy UV-stabilised greenhouse plastic which costs considerably more but lasts much longer. These coverings can be fixed over frames made of wood, metal conduit or plastic pipe.

Size, of course, makes a huge difference in cost. You might choose to build a larger polytunnel from PVC plumbing pipe and greenhouse plastic rather than a smaller one from rigid glazing. It depends on what you want to use the house for.

Even cheaper are mini-greenhouses which basically shelving units or closet-sized spaces, usually with metal frames and rigid or flexible plastic glazing.

Cold frames are like very low greenhouses can cost as little as $0 to build if you can scavenge and recycle materials.

Depending on your location and the type and size of your greenhouse, there are a wide variety of possibilities. If your objective is to grow something specific, then you'll want to build your greenhouse to suit.

If you want to extend the food-growing season, then a simple unheated polytunnel may be enough, or you may want to go for a heated lean-to greenhouse, depending on your climate. A polytunnel will keep hardy greens like corn salad, lettuce, spinach, and kale, and carrots and othre root veg, protected over the winter so you can continue to harvest. A heated greenhouse, especially with supplemental light, can produce more tender leaf vegetables. Peppers and tomatoes need a lot of additional light to make them flower and fruit, as well as heat, so you may need to consider halogen lighting if that's what you want to do.

From the point of view of flower gardening, again a lightweight plastic covered greenhouse will protect semi-hardy and slightly tender plants from moderate frosts, and a heated, lighted house will let you protect and continue to grow your tender plants.

A greenhouse comes into its own in the spring and fall, though, allowing you to get a jump on the season for those heat-loving vegetables like tomatoes, peppers and cucumbers which in many areas are a gamble outside. Or maybe they fruit reliably outdoors in your area but you just want the earliest in the neighborhood! Either way, the greenhouse is your friend. It's especially important if plants will be in the greenhouse all summer, that you have excellent ventilation. My hoophouse has roll-up sides on both long sides so I can roll the plastic up to about 3 feet off the ground and get very good cross-ventilation while still protecting the tomatoes from the rain (which carries blight spores here).