I've had some requests for a follow up on my previous blog on "DIY Greenhouse Over Raised Bed Garden" so I'm going to share some of my secrets in building a greenhouse that will stand up under some fairly extreme weather conditions.
Here in Georgia, we joke about the weather saying, "if you don't like the weather, give it a day and it will change". Literally this past week we went from highs of the 60's to in the 90's. The swings are that extreme. This past winter we had a 4-5 inch snow, under which my little greenhouse held up just fine; though, when I was able I went out and cleared some of the snow from the top. This spring, we've had storms with high winds (gusts up to 50 mph) and with the sides down, we did just fine. If you leave the sides up, it can act like a sail and get some real rattling going on.
The basis of my design was to create a Qunoset-type structure that would distribute the weight as evenly as possible along all of six 3/4 inch white PVC that you can get from any hardware store. These were fit upon metal stakes that were driven just inside the edge of the raise bed and were attached to the bed itself for stability with "U" brackets. I got the metal stakes from an old tent that had long since deteriorated, so the were of no cost. My best guess is that I have around $120 in materials I had to purchase.
Here's a link to a more technical article by the Alabama Cooperative Extension Service on Hobby Greenhouse Construction listing the various types and additional info on their pro's and con's; but for details on how I constructed mine, keep reading!
Parts list - to the best of my recollection:
- 14 - 8ft long 3/4 pvc pipes - schedule 80 (thick wall) - for ribs
- 4 - 8 ft long 3/4 pvc pipes - schedule 40 (thin wall) - for clips
- 12 - "U" brackets to hold the ribs in place
- 12 - 3/4 couplings
- 4 - 3/4 elbow fittings (for door)
- 4 - 3/4 "tee" fitting (for door)
- 2 - 1" couplings (for door hinge)
- 10 - 3" machine bolts with nuts and washers to match (7/16 in )
- PVC glue
- Plastic sheeting (10'x20' )
- 12 metal stakes
- Various other screws and things I had around the house.
With regards to the above list, the important thing to note is that the greenhouse ribs are made from the thick walled PVC and the clips are from the thin walled PVC. Don't get them backwards - you greenhouse won't be as sturdy and you'll rip your fingernails off trying to open the clips wide enough to stay on the ribs!
To start off, I'
ve taken a picture (see below) at an intermediate stage of completion and added some numerical reference points (in yellow) that will help me guide you along in the parts of construction that I'm talking about.
Notice my end-of-season tomato plants above that lasted into late November or so because they were in the greenhouse!
Construction Steps
1. Build PVC Ribs.
I joined two 8 ft sections of pvc together with PVC glue and a 3/4 in coupling to make each of the six ribs. Once the glue dried, I drilled a hole large enough for the machine bolt (you may want to wait for this step until #5 below).
2. Install Metal Rib Posts.
Drove the metal posts at the edge of the bed, at evenly spaced intervals, with about 4 inches of the post remaining above the top of the raised bed's side. I then attached the "U" bracket around the metal post and screwed it into the inside of the raise bed a few inches from the top. Evenly space these along the outside of each raised bed lining them up with the other bed so the ribs will be evenly spaced.
2.5 Secure PVC Ribs (not numbered on the picture)
Placed the 16' PVC rib over the top of one post and bend it down and place it over the top of the corresponding post on the other raised bed. Do this for all 6 ribs.
3. Vertical Stabilizers.
On each inside corner of the both raised beds (total of 4), place a vertical support from the ground to the top of the rib. Mark a line along the top of the rib and cut the support at an angle along this line. Drill a hole through each vertical support and through the outer rib and insert a machine bolt with a washer and nut. Take care to cover any point/edges of the wood with Duct tape in order to protect the plastic covering.
4. Horizontal Stabilizers.
About 3 feet up on each side of the arches, attach a horizontal stabilizer using a 1" x 4" board cut flush with the outer rib arches. Attach these by drilling holes through each rib and board, connecting them with 7/16" bolts and nuts the the head of the bolt on the outside of the rib.
4.5 Build removable shelves for rolling up the sides (not numbered on the diagram).
Cut 2 small blocks out of 1 x 4 wood, bore two holes in the center (a single side block on each side) of the horizontal supports.
Drill two matching holes in the edge of each 1 x 4
block and insert and glue the dowel pegs into the blocks. Cut the dowels/pegs off so that 1 1/2 inches protrude from the blocks. Insert these removable "ledges" to be used to hold up the rolled up sides of the greenhouse for air circulation. (see pic at right)
5. Top Rib Connector.
Make sure that the holes you drilled in the center of the rib coupling is going up and down for the bolt (or wait until after you've installed the ribs to do this step. Attach a 1x4 horizontal stabilizer along the center of the top of the ribs using bolts, nuts and washers. (see picture at left)
6. Horizontal to Vertical Connector.
About 1/2 way up the vertical support in #3 above, attach the horizontal stabilizer to the vertical supports using another piece of 1" x 4" in board (total of 4). The end attached to the vertical support will be square and the end attached to the horizontal stabilizer will be cut at an angle (see pic at right). Initially cut this board too long and mark the angle to cut using the inside of the horizontal stabilizer as your guide. Connect using wood screws. You may want to pre-drill holes here to keep the 1" x 4" boards from splitting.
7. On the back side, the side without the door, I added a horizontal support 1/2 way up (about 3 feet) between the two vertical stabilizers to help tie the two sides together more. I take this one down in the summer when the cover is off so I can walk through from side to side.
8. Similarly, on the side where the door goes (facing my house), I put a horizontal support between the two vertical supports at about 6 feet off the ground. This will become the "header" for the door support and will give me something to attach the side plastic to.
At this point, I realize that this entry has gotten very large. So, I'm going to save the best part for the last episode of the Greenhouse construction post.
Chris
3GT
