Keyhole Gardens are water efficient, easy to maintain and super productive in a small space. Here’s how I built one without breaking the piggy bank.
So I was sitting around late last winter reading the week’s Costco circular when I ran across an article about the success of something called a “keyhole garden” in remote villages of Africa. (What Costco had to do with this, I don’t know.) Intrigued, I dropped the brochure and hopped over to the interwebs to find out what was up with these keyhole gardens.
The backstory on the keyhole garden is that it was developed in the 1990s by researchers in Lesotho, an arid mountain kingdom surrounded by South Africa where they were trying to find a way for remote populations with poor soil, little water and desert-like conditions to build efficient, and sustainable, but low tech, food sources.
The garden’s design is basically a circular raised bed made about 6 feet across with a wedge cut out to allow you to reach a basket at the center of the bed. The bottom of the bed is lined with organic material, sticks, leaves, cardboard, etc. and soil is filled in on top of it. The basket gets buried as well, but the top remains accessible so food scraps, plant trimmings and other organic material can be thrown in and compost will leech back into the bed. The width and height of the keyhole garden makes it easy to water and maintain by hand without bending or reaching too much. Best of all, it’s designed for intensive planting so it yields a whole bunch of produce in a very small space.
I read a couple more websites, looked at some photos of the keyhole gardens others have built, and said “I’m going to build one.” A couple weeks later, I did. Here’s how I did it and the results.
Design the Keyhole Garden
Most of the keyhole garden builds I read used a circular bed about 6 feet in diameter and 2 feet deep with walls made from stones, cinder blocks, bricks, and similar sturdy stuff. The area I wanted to build mine was the old kitchen garden, a 10 ft x 10 ft south-facing patch right outside the door. Not wanting to waste space, I decided to make my garden 8 feet wide with a two foot keyhole opening. I also made the compost basket in the center slightly larger to compensate for the additional planting area.
Because I wasn’t certain this whole keyhole garden thing was going to work out, I decided to skip the cost and effort of dragging (and possibly removing) a ton of stones or blocks to the area and go with a wood wall built like an open top barrel. I chose cedar fence boards as the wood because it was inexpensive, bugs didn’t like it, and held up well in the weather. I used standard 6 in x 6 ft dog-eared fence boards rather than 8 in x 6 ft because the narrower boards were less likely to split. For the “barrel bands” I chose ½-in stainless steel pipe strapping because it was (again) inexpensive and held up well in the weather.
My supplies list:
- 5½-in x 6ft Dog-eared cedar fence boards
- Roll of stainless pipe strap
- ⅝-in screws
- ¼-in x 2 ft wire cloth (for the compost basket)
All of these things are available at any local hardware or home improvement store.
Calculate How Much You Need
Thank a geometry teacher if you can read this
With a supplies list in-hand, the next thing I had to do was to calculate how many cedar boards and screws I was going to need. I planned on cutting the cedar to 18 in, giving me 4 boards for each piece of fencing. Each cut board would need 4 screws to attach it high and low to two bands of pipe strapping. So figuring out the circumference of the bed would tell me the number of cut boards and screws I need.
Except… the bed also has a “wedge” cut out of it that’s 2 ft wide at the edge and 18 in wide in the center where it meets the compost basket. Those extra three pieces (left, right and center) actually make the number of boards required more than just the circumference.
Calculating the circumference of the bed was easy enough:
Or, for my purposes the Circumference = 2 x 3.14 x 4, which just a tad over 25 ft (7.62m). Subtract 2 ft from that for the opening to the keyhole, and you’ve got 23 ft (7m) and change for the outer wall.
(Side note: Mr. Janko, if you’re reading this, I owe you a huge apology. Despite my youthful statements to the contrary a couple decades ago, I did actually end up using geometry for something.)
Figuring out the amount of wood I’d need for the walls of the keyhole was more complicated. I had to determine the base angles of the isosceles triangle that was the “wedge” formed by the keyhole, then determine the intersection of the compost bin and the wedge, and calculate the length of the walls from there.
When that didn’t work, I used a tape measure and eyeballed it.
You should too. It’ll save you a whole bunch of time and some negative consequences that come from calling and threatening your high school geometry teacher in the middle of the night.
Anyway, all told, I needed a minimum of 16 uncut cedar boards, and 18 if I wanted to leave room for splits, cracks, bad measurements and all the other stuff that can happen. I bought 20.
Between the wood, screws and 100 ft of pipe strap, I spent about $100.
Cut your boards to size
I decided to make my keyhole garden 18in instead of 24 in high because there’s a nice view out the dining room window and I didn’t want the garden wall to block half of it. Plus, dropping the size 8 in let me get 4 pieces per fence board rather than 3.
Somewhere between 20 and 350 cuts later, I had my stack of wall pieces.
Building the main wall
The first thing I did was build the main portion of the keyhole garden’s wall — the whole circle except for where the 2 ft keyhole opening would be. For my project that was 51 pieces of 18 in cedar boards (total length divided by the width of each board).
To put the wall together, I laid the boards down side-by-side, evened them up with a 6 ft level, and screwed two sets of pipe strap, one at 6 in from the top edge and another 6in from the bottom. Two screws per strap, four total on each board. When I got to the last board, I extended the the pipe stripe 12 in more and cut it. That piece would be used to join it to the interior wall of the keyhole.
Finally, with the assistance of a helper, we brought the long “snake” of joined boards and stood it up in the garden. We knew where to place the wall because we had used a couple of stakes and a 4 ft length of twine to mark the circle’s boundary.
Assemble the keyhole walls
Once the main wall was in place, we used the same double strap technique to assemble the right and left walls of the keyhole along with the center section where the compost basket would sit.