Extending Your Season with a Greenhouse

Updated: Oct 22, 2020

At our latitude it’s not unusual to see snow on the ground six months of the year – or more. Having such a compressed growing season presents many challenges. Using a greenhouse can help by extending the season and offering protection from extreme temperatures and weather-related damage. But greenhouses can also benefit our friends who live outside of the snowbelt.

Greenhouses can guard against birds and mammals, and reduce exposure to pests, weeds, and disease. They can also make it possible to produce a wider range of plants, bringing exotic items like citrus trees, melons, and eggplants further north than would otherwise be possible.

When calculating the pros and cons of a greenhouse, the first thing that often comes to mind is cost. The good news is that greenhouses can be as varied in size and expense as pickup trucks.

Thinking about extending your season with a greenhouse? Here are a few things to consider about the structure, placement, heating, and ventilation.

Types of Greenhouses

Greenhouses can start as simply as a cold frame or a hotbed, constructed very inexpensively with scrap lumber and clear plastic. Window-mounted greenshouses provide a third small-scale option. While any of these can extend your growing season on a very modest budget, let’s focus on larger alternatives that you can actually step into. Here the first consideration is whether the greenhouse will attach to an existing structure or stand on its own.

The Attached Greenhouse

An attached greenhouse shares a wall with an existing structure, often a house. This saves some construction costs and offers accessibility to the water, power, and heat from the house. It also minimizes the walk to the greenhouse on snowy days.

There are two types, the lean-to and the even-span. The even-span design makes larger builds possible. Regardless of which you choose, the shared side of an attached greenhouse cannot exceed the height and width of the attached structure, so there are built-in size limitations. Plus your plants can’t get sunlight from the shared wall, reducing the total amount of available light.

Finally, if a greenhouse shares heating and ventilation with the attached structure, your ability to control these items separately is likely limited, too.

The Free-standing Greenhouse

Because a free-standing greenhouse shares no existing walls, it’s inherently more expensive. It’s also much more flexible. The only limits on size, location, heat, and ventilation are your property lines, budget, and any applicable building codes.

Among the popular designs, most fall into three roof designs; triangular, gutter-connected, and curved.

Triangular Roofs

These traditional-looking greenhouses include the gable, even-span, and A-frame designs. They offer maximum sunlight and lots of headroom (particularly in the center). However, they typically use glass floor to ceiling, which requires more significant (and expensive) framing.

Gutter-connected Roofs