Greenhouses offer advantages even to the hobby gardener. They extend the growing season by letting you start seeds earlier in the spring and continue growing plants into late autumn, even winter, depending on your local climate and greenhouse setup. However, rising construction costs put greenhouses out of reach for many gardeners. Fortunately, it is possible to build a greenhouse for very little money.

Many gardeners would like to have a greenhouse to extend their growing season, but can’t afford the high cost of a commercially bought greenhouse. With some effort and creativity, you can build your own greenhouse that can provide you with the same benefits of a commercial greenhouse at a fraction of the cost.

Ideas For Low Cost Greenhouses

Plastic

You can build a greenhouse using PVC pipe and sheets of plastic. PVC pipe of 3/8-inch diameter is flexible enough to bend into semi-circles, creating a framework for a Quonset hut-style greenhouse that can be covered with plastic. This type of greenhouse can be built in nearly any size, and will hold in a surprising amount of heat from the sun, given that its walls are made of a single sheet of plastic.

Glass

A more permanent and durable greenhouse can be built out of sheets of glass, although this requires more work than a plastic greenhouse. Storm windows and used windows are widely available through architectural salvage yards, used building materials stores and private individuals. Many people simply throw away or give away their old windows when they replace them with new, insulated windows. Old windows can make very effective greenhouses, particularly if you are able to acquire a large number of windows that are the same dimensions. Build a framework to hold the windows, install the windows, and you have a nearly free greenhouse.

Cold Frames

A cold frame is essentially a miniature greenhouse. A cold frame can be constructed by building a wooden box with an open bottom and a top that is tilted toward the sun and covered by a hinged window. Put the cold frame over seedlings in the garden, and the effect is the same as if they were in a greenhouse. By hinging the window on top of the frame, you enable yourself to lift it up to tend the plants inside the cold frame.

House Extensions

You can make a greenhouse that can double as a pleasant sitting room by building a glass-covered addition to the south side of your house. This saves money because the back wall of your greenhouse is the wall of your house, so is already built. By building the rest of the greenhouse using salvaged and used materials, you can save even more money. This arrangement also makes greens that are growing in your greenhouse easily accessible from your kitchen.

Building Your Own – A Simple Guide

The North Carolina Cooperative Extension Service offers plans for an inexpensive greenhouse using low-cost PVC pipe and plastic sheeting. Using salvaged or recycled materials can lower the cost even more.

Things You’ll Need

• 4 pine posts, 4-by-4 inches, 2 feet long
• 2 treated pine boards, 2-by-6 inches, 14 feet long
• 2 treated pine boards, 2-by-6 inches, 12 feet long
• 32 galvanized electric metallic tubing straps, 3/4-inch
• PVC cement
• 16 PVC pipes, 3/4-inch, 10 feet long
• 6 PVC crosses, 3/4-inch
• 2 PVC tees, 3/4-inch
• 4 treated pine two-by-fours, 6 feet long
• 2 treated pine two-by-fours, 3 feet long
• Door
• Hinges
• Sheet of 4-millimeter plastic, 24-by-20 feet
• Staples
• Heavy-duty stapler
• Nails and screws

Instructions

1. Choose a site. The West Virginia University Extension Service recommends the south or southeast side of any large structures or shade trees. Plants respond best to morning light, so favor sites that receive direct sun in the morning. The site should drain well and provide convenient access to water and tools.
2. Dig out the high side of the site so the foundation boards will be level. Place the 4-by-4 posts upright at each corner to anchor the structure and keep it from blowing over in high winds.
3. Nail the 12- and 14-foot boards to the posts so they are level with the top of the posts to form the greenhouse’s 12-by-14-foot foundation.
4. Attach the electric metallic tubing, or EMT, clamps to the side boards of the foundation using wood screws; space the clamps at 2-foot intervals. These will hold the PVC pipe ribs that arch over the structure. Do not tighten the EMT clamps until the PVC ribs are in place.
5. Cut the midrib pipe into 22.5-inch pieces and link them together with six PVC crosses to form the midrib. Cap the ends of the midrib with two PVC tees. Glue the pieces together with PVC cement.
6. Lay out 16 pieces of 10-foot PVC pipe. These will act as the ribs of the greenhouse. Glue them into the PVC tees and crosses using the PVC cement.
7. Bend the ribs and attach them to the foundation with the EMT clamps. Completing this step requires assistance from one or two additional people to avoid breaking the joints you’ve just sealed. Tighten the EMT clamps.
8. Construct two wooden rectangular frames to fit at each end of the greenhouse using the 6-foot and 3-foot boards. One of the frames will accommodate the door, so it should be sized to fit. Attach the door with hinges.
9. Stretch the plastic cover material over the frame and staple it into place. Allow some extra material at the bottom of either side and bury it in the soil to prevent animals from entering the greenhouse.

Tips & Warnings

To keep the greenhouse warm during colder weather, paint barrels or milk jugs black, fill them with water and stack them in the greenhouse where direct sunlight will hit them. The water heated inside will cool slowly overnight, releasing heat to keep temperatures up in the greenhouse. For cleaning greenhouses see this guide.

Recommendations on the Dollar Stretcher website suggest saving money by watching your local newspaper for demolition sales or contacting local stores to see if they have any old doors and windows you can use when building the greenhouse.

Photo by Johannes Hofmann on Unsplash