Greenhouses: Sunrooms for vegetation

Jan. 26, 2013 @ 07:22 PM


One of the most enjoyable gardening activities I’ve experienced is raising plants in a greenhouse. It is immensely pleasurable to see the results of your own labor develop into hundreds of healthy baby plants. And while starting seeds and rooting cuttings can be done in many improvised locations (basement, spare room, dining room table), having a dedicated space that is designed for the task makes all the difference. And it’s possible to have that without taking out a second mortgage.

A good starting point is to project how much space you will need. If all you want is space to raise transplants for a small vegetable garden and root a few cuttings from your shrubbery, then 20 or 30 square feet of “bench” space may suffice. In that case, a six-foot by eight-foot structure may suffice. That would provide space for two-foot wide benches on either side, with a two-foot wide aisle down the middle.

If, however, you have an extensive collection of patio plants and hanging baskets you’d like to overwinter, a larger greenhouse may be in order. Spending a few minutes with some graph paper to consider various arrangements will really pay off. Be sure to consider location while you’re at the drawing table, with full sun being critical.

While it is perfectly acceptable to simply place plants directly on the ground, I have always found it much more pleasant to work at counter-height benches. That also provides space underneath for supplies and even for raising plants that don’t need direct sunlight (e.g. overwintered hanging baskets that are semi-dormant).

Something in the six-by-eight or eight-by-twelve size range can be assembled easily and inexpensively by constructing a frame of lumber, metal pipes, or even PVC pipe. Simply cover the frame with plastic sheeting, and you are in business!

For something more permanent (and perhaps more attractive!), consider purchasing a greenhouse kit of the appropriate size. In that case, I suggest you look at double-wall polycarbonate as your cover material. Double-wall polycarbonate is similar to corrugated cardboard, with two outer layers and ribs in between. Those ribs provide stiffness, and also airspace which helps insulate the greenhouse.

Of course to truly qualify as a greenhouse, you will need a heat source. Your main fuel options are electricity and gas. I suggest you get professional advice on this matter since uncontrolled combustion and electrocution are plausible outcomes.

Leaving it unheated is also a perfectly acceptable option, but technically you have a cold-frame instead of a greenhouse, and a shorter useful season. Tomato transplants, for example, could be started mid-March in a heated greenhouse, but with a cold-farm it might be safer to wait until early to mid-April.

Ventilation is critical, for managing both temperature and humidity. Fans are ideal, but see previous note regarding electrocution risk. At a minimum, include a door and/or window at each end to allow cross-breezes.

Of course, there are other possible uses for a greenhouse, such as producing vegetables over the winter, raising orchids, or even bananas and oranges. And instead of benches with pots, it is perfectly acceptable to create raised beds directly on the ground.

Whether you are a hobby gardener or a small farmer, a backyard greenhouse can be a valuable and enjoyable tool for increasing production.