Monday, February 2, 2015

Your Own DIY Lean-To Greenhouse

Finally! I have my own small walk-in greenhouse! After starting seeds indoors and moving them to finicky, bulky mini-hoop houses for years, I can actually walk into a space that's flooded with seedlings in an easier-to control environment. You can do this, too, even if you're not very "handy." I don't consider myself "handy," but I'm willing to learn and try new things, and that seems to work (with one proviso: my method of building this was VERY cheap - total cost was $137 - and because I used PVC, thin 2mil plastic sheeting and not a more expensive, thicker UV-resistant sheeting, and plastic tie-wraps, I know this structure will need regular maintenance, but ultimately I think it will be a better investment than a pre-fab unit, for the reasons outlined here).

So here's how to build your own 6'x10' lean-to greenhouse:

1. Drill a pressure-treated 2x4x10 with 1" holes drilled every 2 feet level into studs along the back wall on the south-facing wall of your home. I lined this up with the halfway point on one of my windows for reasons described below.

2. On the ground 6 feet away, hammer 1/2"x2' rebar 1 foot into the ground spaced 2' apart, lined up square with the holes you drilled on the 10' board on the wall.

3. Measure and attach a 2x4 vertically from your top board to the ground surface, and attach another measured and cut 2x4 along the ground (checking to make sure it's level) using heavy-duty tie-wraps.

4. Take 3/4" x 10' PVC pipe (I had to extend it by one foot using couplers and another piece of pipe), set it onto your ground-implanted rebar, and gently arc it until you can get it to snap into the corresponding hole in the board on the wall. (Never mind the T-bar PVC cross section you see in the picture - that was a mistake!)
5. Frame in your planned door (fortunately my amazing wife had already made one that we were no longer using in an old chicken coop), making sure that the top piece is level (my picture looks a little crooked!). FYI: I notched in the top and bottom on the vertical pieces so that the would attach flush without jutting out an causing the plastic to stretch.
5. Mimic the exact structure on the side that doesn't have a door, and attach a 2x4x10 just below door height from one end of the structure to the other, attaching it to each PVC rib with tie-wraps. This will provide rigidity and allow you to hang plants or tools later.
6. Attach your plastic sheeting using 4" snap-clamps (I got mine from, making sure you double-over the plastic so it won't tear when you clamp it. Make sure you leave a foot or more overlap on the bottom. Cover this with dirt.
7. Reinforce the plastic sheeting on the outside using furring strips (see picture of door below for an example). This is VERY important, as simply stapling the plastic to the wood structure will simply cause tears when the wind blows.
8. Attach your door and create a genius closing mechanism like this one!

9. Make sure you create a ventilation system, as I've noted that on a 40-degree sunny day, the inside of the greenhouse can be 80 degrees at floor level, and closer to 100 degrees at 6-foot height. You don't want to cook your plants! I used self-adhesive Velcro on the door (and I have yet to install it on the other end as well) to provide ventilation.

10. If you were able to utilize one of your home's windows in the design, vent the warm air into your home on cold days to take advantage of passive solar radiation. This pass-through is also handy for moving seedling flats in and out of the greenhouse on really cold nights.

11. Install a shelf and some plants! Notice I've also used old election sign wire as frames to hold my row cover sheets over seedlings on cold nights. This "double-insulation" method has been shown to be extremely effective by Eliott Coleman in his book, The Winter Harvest Handbook.
And there you have it! As time goes on you may decide to install a full-length shelf or two down the length of the structure. You can also leave the ground bare and grow salad crops and cold-hardy veggies all winter long. If you'd like more information about how to build your own greenhouse cheap, feel free to contact me.
Happy growing!