Building a Greenhouse: Part 1

Many gardeners consider a greenhouse a necessity for wintering non-hardy plants and starting new plants, as well as protecting sensitive plants from summer’s heat. A greenhouse as defined by the Gardener’s Dictionary is “a structure, covered with glass, fiberglass, or plastic, in which temperature and humidity can be controlled, for the cultivation and/or protection of plants.”

If you are considering building your first greenhouse, know that this needn’t be an expensive or hugely time-consuming project. However, whether your greenhouse is to be low budget or deluxe, the key to success as with most gardening endeavors is careful planning. This article will outline the basics so that when you contact a local Master Gardener’s program or university extension service, you will already have a good idea of how you want to proceed and a list of good questions prepared. This will also help you to decide on what type of blueprint to search for online or at your library where in both places you can find many good ones at no charge.

With several types of greenhouses from which to choose, the final decision should be based upon factors such as the amount of growing space you want, the available sites, budget, and last but not least, the environment required by your plants whether they be water garden tropicals, kitchen herbs or non hardy vegetables.

As you probably already know, a greenhouse receives heat through solar radiation. Greenhouses in the colder and/or less sunny regions or greenhouse with poor heat retention need a supplemental heat source, such as electric heat. That said, here is our intro to building a greenhouse.

Attached

An attached greenhouse can be a lean-to or full-size structure, or it can be an extended window structure. Some of the advantages to an attached greenhouse are the close proximity to electricity, water and a heat supply. Disadvantages include limited sunlight, possible space and ventilation limitations, uneven temperatures, and possible problems with snow and/or heavy rain from the home’s roof.

An even-span greenhouse is a full-size structure that has one gable end attached to another building. This is usually the largest and most costly option, but it provides more usable space (two to three benches), can be lengthened, and is better formed for air circulation and maintaining uniform temperatures during the winter.

Freestanding

A freestanding greenhouse lends itself to more location choices, and because it’s set apart from a building, more sun. It can be as big as you want. The disadvantage is that it requires a separate heat source from the home (unless solar heating is all that’s needed).

A 17 by 18-foot freestanding greenhouse or even-span, attached greenhouse provides one of the best ratios of cost to growing space. Such a greenhouse can house a central bench, two side benches, and two walkways.

Planning for adequate bench space, storage space, and room for future expansion is an important step in building a greenhouse. While one may think a small greenhouse’s climate is easier to maintain, in actuality, large greenhouses are easier because due to their increased air volume, their temperatures don’t fluctuate as much as in small ones. Plan for a minimum of 6 by 12 feet.

Build your greenhouse where it will receive maximum sunlight, such as on the southeast side of a building or shade trees. Sunlight all day is best, but morning sunlight on the east side is sufficient because it allows the plant’s food production process to begin early. North of major structures is the least desirable location. The National Sustainable Agriculture’s Website offers detailed and scientific information on finding the best location for your greenhouse in your particular area.

Deciduous shade trees are helpful in protecting from summer’s late afternoon sun, but your plants shouldn’t be shaded in the morning. Also, be sure the shade trees are deciduous so that their bare branches in the fall and winter let in maximum sunlight.

Also, when considering location, look at drainage, your specific plant’s requirements and shelter from winter wind, as well as accessibility to you and to heat, water, and electricity sources. Part two of this article gets into the nuts and bolts of the structures.