How to Build a Greenhouse in 4 Easy Steps 

No longer just the purview of your local horticulture society, learning how to build a greenhouse—a wonder for a backyard garden—is something you can do as well. A simple DIY greenhouse can nurture flowers out of season, keep houseplants cozy all winter, and cultivate plants in a region with a natural climate that would otherwise be too cold. What seems like a prevalent backyard structure today is first linked to the Roman Emperor Tiberius back in 30 AD, who had to eat a cucumber a day to keep the sickness away (seriously). His gardeners built a cucumber palace with stone walls and a glass ceiling to keep up with the harvest. Less powerful Romans resorted to greenhouses called speculariums, which consisted of potted plants covered in a transparent mineral called mica.

By 1663, Louis XIV had the Palace of Versailles orangery to house the citrus trees from Italy, Spain, and Portugal. Eventually, the two-sided gallery—protected from the elements by stone walls and south-facing double windows—stretched about 165 yards long, with 42-foot-hight vaulted ceilings.

Today you can see amazing glass greenhouse around the world, and even a kinetic glasshouse that unfolds in four minutes. Yet most backyard greenhouses remain humble, practical structures that allow gardeners to jumpstart crops. Want oranges in Cincinnati? It’s possible if you have a greenhouse. 

Amanda Amstutz, supervisor of public programming at the Foellinger-Freimann Botanical Conservatory in Fort Wayne, Indiana, says, “The backyard gardener can get a head start on their seedlings and is able to transplant and harden off their plants.” With a greenhouse, you can start your seedlings in trays by February, and by April expect full-fledged plants to plant in the ground. So, whether you want to grow the odd palm or feed your family with fresh veggies from the garden year-round, here’s everything you need to know about how to build a greenhouse, even if you’re not royalty.

How to choose the best greenhouse?

Greenhouses come in all shapes, sizes, and materials, and have a similarly diverse ability to serve different functions. The first thing you want to consider before you learn how to build a greenhouse is whether it should be a temporary structure or something fit for the long haul. The easiest backyard greenhouses to assemble are temporary greenhouse kits. These are generally covered in flexible plastic cover and utilize lightweight metal frames, says Steven Engel, regional account manager for PanAmerican Seed in Chicago. “On the other hand, for permanent backyard greenhouses,” he says, “I prefer to use double-walled polycarbonate panels. Double-walled polycarbonate offers better heat retention.” 

Alternatively, you might start with a temporary structure and then later decide to build a permanent one. “Starting with a temporary-type greenhouse that can be easily moved and disassembled will provide flexibility in discovering what you really need in a greenhouse,” says Lindsay Pangborn, plant expert at online plant retailer Bloomscape. “Things like size and site placement can vary quite a bit from what you may have expected.” 

What are the different types of greenhouses?

The first common type of greenhouse is a cold frame. The smallest and simplest kind, these greenhouses are affixed onto the side of a house. They usually have a wooden structure about three feet tall with a hinged glass lid on top. If they have access to sunlight, an additional heat source isn’t required. “It’s a great place to sow winter carrots and garlic, as well as over winter roses in pots and other plants marginal to our winters,” says David Angelov, CEO of PlantParenthood in Swampscott, Massachusetts. “Nothing inside should freeze over, and it will be exposed to as much sun as possible during the winter.”

The second type of greenhouse is a self-supporting and complete, stand-alone building. A greenhouse doesn’t always need additional heating, as the inside is warmed by the sun’s rays trapped by glass or plastic panels. But an extra heating system can be beneficial to greenhouses in regions that get less sun throughout the year. “They stay warm with a heating system and are most often vented constantly to allow air flow and humidity control,” Angelov says. Whether heated just by the sun's rays or with additional heating systems, good airflow is important to your standalone greenhouse. The last thing you want is inadequate ventilation, which could lead to stagnant air, a potential cause of plant diseases. “Airflow also prevents too much heat buildup during the warm parts of the year,” Engel adds.

How to build a greenhouse?

Now that you’ve determined the greenhouse type you want, you need to obtain greenhouse plans. Pick the plans that suit your budget and plot space. If you’re a novice, consult with your local nursery. Now you are ready to build. Read on for all the steps to making your greenhouse green and great.

Whether a cold frame or a standalone greenhouse, your structure needs to have access to sunlight. “Avoid placing the greenhouse under trees or too close to other buildings that may provide unintentional shade,” Engel says. “Also avoid areas where water naturally pools or flows.” 

For a freestanding greenhouse, it is best to build north to south. This way, both sides of the greenhouse can benefit from the same amount of light, Amstutz says. “One side will benefit from the morning sun in the east, while the other will benefit from the sun setting in the west.”

In regions that don’t get much sunlight at all, consider locating the greenhouse to whatever side of your plot has access to electricity, which comes recommended by landscape designer, Camille Cimino of the Nature of Things in Los Angeles, who once worked on a cut flower farm in the Arkansas Ozark Mountains. There, the greenhouse was heated by two massive woodstoves. “I loved the way the greenhouse felt and smelled; it was warm and humid and smokey and full of life,” she recalls. Cast iron stoves and woodstoves can work all winter to keep your plants warm.

If working with an uneven outdoor space, level the area housing your greenhouse. Uneven ground can drown your plants as water pools and accumulates in the greenhouse. For cold-climate gardening, make sure the base of your greenhouse is lower than the frost line. Doing so will keep your plants warm during the chilly months. 

You will also want to create a weed barrier on the floor of your greenhouse. “I prefer to add small rocks or pebbles over the weed barrier,” Engel says. He also adds a few inches of rocks and pebbles lining the outside of the greenhouse to keep grass and weeds from growing right next to it. “With these barriers, you can also be in the greenhouse and not get muddy when working or watering.” 

Follow the directions in your greenhouse plans and build your greenhouse. Trim the plastic tubing or wood pieces to the correct lengths, and then assemble them using the proper hardware and adhesives. For instance, snap on clamps holds poly film and plastic sheets in place and clear greenhouse plastic film is a savior when building temporary structures.

Depending on your individual greenhouse plans, you can use any combination of materials to cover your greenhouse from basic plastic sheeting to polycarbonate panels to actual glass for the more permanent structures. However, if you forgo a greenhouse plan entirely, Engel recommends using treated lumber and using a water sealant on the lumber prior to construction. “To minimize movement in high winds, make sure the greenhouse is well anchored to the ground. Concrete posts into the ground are the best option.”

Adequate ventilation and air flow is a must in your greenhouse. “This prevents stagnant air, which could trap or encourage plant diseases,” says Engel. Airflow can also keep your greenhouse cool enough to prevent heat buildup during summer that could kill plants and attract swarms of bugs. “Because greenhouses are closed environments, they can harbor a variety of pests such as mites, whitefly, aphids, and scale,” Cimino says. “Once pests lay eggs in the soil, it can be difficult to manage infestations.” 

Ideally, your greenhouse should mimic the environment in which your plants grow. Amstutz adds, “Control the greenhouse climate as to not limit photosynthetic activity or deplete concentration levels of carbon dioxide.” Make sure there is enough air circulation and to discourage mold, fungus, and mildew from forming. And finally, for larger greenhouses, add roof vents or circulation systems to keep your everything aerated.