Building a Productive, Safe Greenhouse For Less Than $1,000
Extend Your Growing Season
Reading Time: 9 minutes
By Romie Holl, Wisconsin
With the short growing season in Wisconsin and the price of some plants in the nursery, I came to the conclusion that I needed a greenhouse to start my plants from seed instead of buying plants every year.
I stopped in to visit several people who had greenhouses (both commercial and residential) to find out if they were happy with the model they had, and what they would change if they could do it over again. Almost all the residential people said they wished their greenhouse was bigger, and the commercial greenhouses said they had to replace the plastic every five to 10 years.
After looking at the options — replace the plastic every few years or spend thousands on a glass model — I decided to build my own. Remodeling my place from top to bottom, I am often walking around the big box home stores and the local Habitat for Humanity Restore. Restore gets items from houses being torn down or remodeled, and sells the items to pay for building new houses.
The Restore has everything for a house, including windows and doors. I decided on patio doors for my greenhouse for several reasons. First, the doors are the same height (usually 79 to 80 inches tall), making it easy to build a frame for them. Secondly, the doors are double glazed (two glass panels) and more efficient. And thirdly, I struck a deal with the Restore manager that I would buy any patio door for $10 (no frame) roughly 36 inches wide.
To work, a greenhouse has to be in the sun, which sounds obvious. Not only should it be on the south side of the house (or east if necessary), but it should be far enough away from any trees and buildings that could block the sun. On the south side of my place, I have a 10-foot-wide covered porch and I wanted the greenhouse to be as close to the kitchen as possible (nothing like going out and picking fresh rosemary when cooking).
Once the site is picked, you have to decide what size to make the greenhouse. With 3-foot wide doors, each side could be 6-, 9-, 12- or 15-feet long. I decided to use 8-by-8 timbers in the corners and use five patio doors per side. The extra wide timbers in the corners will make up for any discrepancy in the door width (sometimes you get a 34- or 38-inch-wide door). I live on a hill and I built a deck to support the greenhouse; on top of the deck, I applied rubber roofing to waterproof the green treated plywood, making it safe to use a water hose inside the greenhouse.
In total, this greenhouse cost just under $1,000 to build. This does not include the cost of building the deck that supports the greenhouse. I was able to keep it at this price because of buying the doors at Restore and finding the closet shelving on Craigslist from people who were remodeling.
Future plans for the greenhouse include adding aquaponics. Since my greenhouse is built on a deck, there is roughly five feet of space underneath it. I will be getting a stock tank (500 or 1,000 gallons). After insulating the tank, I will start to raise perch (or tilapia) using a pump to get the water from the fish tank to the greenhouse so the plants will use the enriched water, and after running the water through the plants, the water will be returned clean for the fish to use. This way I will be able to grow 200 pounds of fish per year as well as all the veggies I need. This method also forces you to grow organically because chemicals that could be used on plants would hurt the fish. I will also be adding an automatic drip system to water the plants, freeing up time for other projects.
HOW I BUILT IT
STEP 1: FRAMING
1. I notched the 8-by-8 posts, so when the 2-by-12s were added, they were flush with the posts. This way you can place the patio door flush with the supports and screw them on (I used 2.5-inch decking screws). The bottom of the 2-by-12 should be 77 inches to 78 inches from the floor, as this will allow you two or three inches on top to screw the doors in place.
2. The next step is to place the middle posts (eight feet from each end) and to put in 2-by-6 angle braces to make the structure is rigid. This is also a good time to paint the wood before you start screwing on the patio doors. Between the bottom of the posts, I used 2-by-6 boards to providing extra room to screw the bottom of the doors in place. I did not put any support between the doors because the wood around the glass in the door is its own support. I left the middle post long (12 feet). This will be trimmed once I have the roof rafters in place.
3.The manager of Restore called me and told me he had eight doors ready for me. I picked them up and my son and I put seven of the doors in place within an hour after getting home. Just make sure you put the “inside” of the patio door inside the greenhouse and have the vinyl or aluminum on the outside.
STEP 2: TABLES AND STORAGE
4. While I was waiting for more patio doors, I decided to build the tables for the plants, using 4-by-4s for the posts and 2-by-4s for the side. I wanted the tables to be at waist height, making it easy to work with the plants, so they are 32 inches tall, and the width is 36 inches. I can reach across this easily. A bottom shelf that is 8 inches off the ground will be used for storage. Having the tables in place around the perimeter will make it easier to install the roof rafters. (I put down boards and walked on them.) I also bought and installed a casement window for airflow in the greenhouse ($25 at Restore).
5. I then built a middle workbench that was 4 feet wide and 7 feet long (32-inches tall again), which leaves me a 3-foot walkway all the way around the greenhouse.
6. As I get more patio doors, I put them up and then I keep busy with other items in the greenhouse. On the middle workbench, I used 2-by-10s and plywood to make a place where I can mix up soil and pot the plants. I also put up a 2-by-4 all around the perimeter of the greenhouse around 5 feet high. Not only does this make the structure stronger, it allows me to add shelving for even more plants and flats. I chose this height because I am over 6 feet tall and can see the flats easily; this also allows 24 inches between the table height and the bottom of the top shelf leaving plenty of room to have bigger plants on the table.
7. Using 4-by-4 posts as frames, I used one of the patio doors as the door to get in the greenhouse.
STEP 3: THE ROOF
8. I was as far as I could get on the bottom half of the greenhouse, so it was time to start working on the roof. I put up the first 2-by-12 in place. The sidewalls are 7-1/2 feet tall and the middle is 9-1/2 feet tall. Once the first 2-by-12 was in place, I glued the second 2-by-12 boards together using nails and decking screws to hold them. I came back later and used 3/8-inch grade 5 bolts to make sure they will not come apart. I climbed on the roof of the house to see how everything looked. I placed a mark on each 2-by-12 (16 inches on center) where the roof rafters will go, as this way I won’t have to measure each one while I am nailing them in place. You will also notice that there is a second 2-by-12 around the perimeter of the greenhouse; these went up after the doors were in place, and this covers the top of the doors helping them to be waterproof.
9. I cut and painted all the rafters (made from 2-by-8s) before I put them up. At first I just toenailed them in place, but later I came back and installed the metal brackets to hold them permanently in place. After the metal brackets were in place, I also put blocking up between the rafters for extra strength.
10. For extra strength, I installed cross braces on the rafters. This will let me hang 2-inch diameter pipe so I can have hanging baskets and be able to slide them where I want.
11. To fill in the cracks between the doors, I first used the “door and window” grade caulk. On top of that, I used silicone caulk to waterproof everything. Since the roof rafters were now up, I could build the second level of shelving. (It would have been in my way installing the rafters.) These are 24 inches wide (two 12 inch wide wire closet shelving). This width was chosen because the top shelf is where I start all of my flats (each flat is 11 inches wide and 21 inches long). With the amount of shelving I have, I am able to start 50 flats at the same time, and still have the bottom tables to handle the bigger plants. I am choosing this type of shelving because it will allow water to flow from the top set of plants to the bottom set of plants, and it also lets light through.
12. I covered the end caps of the rafters and it was time to install the roof. I did not want to use glass for the roof of the green house, not only because of the extra weight of the glass but hail could break it. If you know what metal roofing is (corrugated steel), you can find clear polycarbonate that has the same shape—and it is a lot lighter than glass. It is also 10 times stronger, lets in 95 percent of light and has a 20-year hail and anti-fade warranty on it.
STEP 4: BRING IN THE PLANTS
13. With the roof in place and the closet shelving installed on the tables and upper shelves, it was time to start bringing in the first set of plants. Admittedly the greenhouse looks empty when I brought in all the plants I had in the house. In the corners of my work bench, I screwed down two containers. One holds bamboo skewers, which I use to hold the seed packages when I plant. In the basket I have the items I use to check the pH level of the pots.
14. Since the greenhouse is so close to the house, it was easy to run electricity and water to it (the water is turned off in winter and I water by hand). I added lights so I could see at night and a ceiling fan so the plants would have air movement and become stronger. If there is no air movement the plants grow straight and skinny and will be weak, the air pushing them around makes the plant get thicker stems and will be a lot stronger and hardier.
15. It is amazing how the greenhouse works. With no auxiliary heat in the greenhouse, you can see there is a 40-degree difference between outside and inside the greenhouse.
16. Because the greenhouse can get hot enough to burn plants, I bought two automatic openers for the windows. They open and close with the temperature and are adjustable.
17. The greenhouse has my full garden started eight weeks prior to when I normally plant. Two weeks after I planted, it was time to start thinning out the seedlings, and there is nothing like playing in the dirt while looking at the snow outside the greenhouse.
Romie Holl writes and homesteads from Campbellsport, Wisconsin. Look for more of her how-tos and construction projects in upcoming issues.