When you rely on the sale of plants or vegetables as part of your income, you know winter can slam the brakes on your farm’s earning potential. Thankfully, with a greenhouse, there is an easy way to show Jack Frost who’s really in charge.
Setting up a greenhouse on your farm can extend your growing season amd protect your seedlings from cold. It also gives you and your plants a sunny haven to while away the offseason.
Greenhouses have deep roots in American history, but they aren’t an American invention.
The first greenhouse appeared in ancient Rome around A.D. 30. It was built for Emperor Tiberius, who enjoyed eating a single cucumber each day year-round for health reasons.
Agricultural writer Gaius Plinius Secundus (Pliny the Elder) lived during the reign of Tiberius and wrote about these structures. He noted that they consisted of beds mounted on wheels which were moved out into the sun. They were then withdrawn under the cover of frames glazed with transparent stone on winter days.
Fast forward to the 1700s, and the greenhouse made its first appearance on American soil. By 1787, George Washington had built a structure at his Mount Vernon estate in Virginia to grow, of all things, pineapples.
The Mount Vernon Ladies’ Association of the Union, nonprofit that owns and maintains Mount Vernon, states the following:
“The greenhouse—at the time an unusual feature on the American landscape—allowed Washington to nurture tropical and semitropical plants. Lemon and orange trees and sago palms grew here, much to the delight of strolling guests. An ambitious structure for its day, the greenhouse had many windows to capture the southern sun, a vaulted ceiling that promoted air circulation, and an ingenious heating system that generated radiant heat from a series of flues under the floor.”
These days, you don’t have to be an emperor or leader of the free world to own a greenhouse. You just need a desire to keep growing, no matter the season!
Knowing Your R-Value
Washington must have known that when you have a greenhouse, your growing season doesn’t need to end when winter begins.
The buildings retain the heat of the sun as it passes through a transparent or semitransparent material. Warm air is generated inside, and because the warm air has nowhere to go, the temperature inside your greenhouse will rise.
Your greenhouse’s ability to retain heat will depend on the insulating capabilities of the material it’s made from. Knowing the R-value, the metric for rating insulating materials, of your choices will help you understand how much heat loss you’ll have. The higher the R-value is, the better.
Three of the most popular types of greenhouse are:
- Cape Cod-style
- DIY, old-window
Each will offer different levels of heat retention, durability and cost.
Cape Cod Greenhouse
If you’re dreaming of a beautiful greenhouse, it might be the Cape Cod-style you’re wishing for. The most expensive of the three, this style of greenhouse has a peaked roof for room to grow saplings, install side shelves or hang rows of baskets.
Cape Cod-style greenhouse kits have frames made from aluminum, steel, wood or plastic. Some types will require you to attach the frame to a base of 4-by-4 beams or cement blocks.
A Cape Cod greenhouse is easy to grow in. Most have automatic venting, so when summer heat causes temperatures to rise, vents will automatically open. If you have access to power, you can add fans for airflow or heaters for stable temperatures.
The cost and durability of a Cape Cod greenhouse will depend on the material selected for walls and roof, the size of the greenhouse and any extras you add. When choosing a kit, make sure the material you choose offers the type of heat retention you’re seeking. Also ensure it is strong enough to handle your snow and wind levels.
A Cape Cod greenhouse will protect your plants and extend your growing season. While this style of greenhouse is expensive, it’s also beautiful and built to last.
DIY, Old-Window Greenhouse
When your old windows have outlived their usefulness, you can up-cycle them into an inexpensive DIY greenhouse.
For materials, you just need salvaged windows and wood. Depending on the size you’d like, it may take anywhere from a few hours to a few days to build.
There’s a lot of inspiration online for greenhouses made from old windows. And you can copy someone else’s style or invent your own.
To build, you’ll need to lay out your windows and decide on a pattern. Each window needs to be supported by a frame. Otherwise, your entire structure could collapse.
If you want your roof to offer diffused light, you can use fiberglass panels instead of glass. Are you using antique windows with wood casings? You may want to add flashing tape around the base to prevent rot over time.
If you want a greenhouse that’s Pinterest-worthy and simple to build, this is the style for you. It’s even better if you own lumber and old windows, as it will cost nothing more than your time.
While it will extend your growing season and look great in photos, this style of greenhouse may not protect your plants in the thick of winter. It could also collapse under heavy snow or wind.
For an easy-to-build greenhouse that’s big on space and low on budget, a polyurethane greenhouse is a popular choice. If built correctly, you should only need to replace the material every few years.
To build this type of greenhouse, you’ll need to stretch sheets of polyurethane over a frame made of aluminum, steel, wood or plastic.
You can buy hoop-house frames. But to cut costs you could build your own or even improvise with the frame of a car shelter. Just make sure the frame is curved so snow doesn’t build up on the roof.
Which polyurethane should you use? Although several thicknesses of plastic film are available, the 6-mil thickness is the standard.
“It is available in many widths up to 50 feet and in standard lengths of 50 to 100 feet,” write the editors in Ortho’s All About Greenhouses. “At 10 to 15 cents per square foot, you can cover a hobby greenhouse for a modest cost.”
A polyurethane greenhouse is a quick and cost-effective way of setting up a greenhouse. As long as you anchor it down and add a vent so heat will escape in the summer, you’ll keep your thumb green for most of the year.
In early spring, the trees and greens are just starting to send out leaves. “But in the greenhouse, you bite into a fresh, juicy tomato that you have just plucked from a vine,” writes Roger Marshall in The Greenhouse Gardener’s Manual. “Nearby, key limes and organs await harvesting, their citrusy aroma wafting through the warm, humid air.”
These are just some of the pleasures of owning a home greenhouse. Whether you’d like a jump start on spring planting or just need a safe place to grow exotic trees, a greenhouse might just be the next thing to expand your hobby farm.
Sidebar: Know Your Snow Load
When you invest in a greenhouse, you want it to stand the test of time. Unfortunately, thanks to wind and snow damage, it can be pretty common to have shattered glass, ripped out panels or even structural collapse.
Budget is always a factor when building structures, but greenhouses with a guaranteed snow load and wind rating are worth the investment.
“Our standard greenhouses are rated for 85-mile-per-hour winds and 32-pounds-per-square-feet for snow,” says Angela Drake, marketing director for BC Greenhouses Builders in Canada. “You can upgrade to sustain even higher loads of snow and wind, with strength for up to 100 psf of snow and 140 mph hurricane-force winds.”
Before choosing your greenhouse, ask your local municipality for local snow and wind ratings. You can compare your ratings to the type of greenhouse you’re interested in, and you’ll know what to expect when winter arrives.
This article originally appeared in the January/February 2020 issue of Hobby Farms magazine.