Keyhole Garden

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Gardening in South Texas is no joke...drought, torrential rain, pests, you name it.  This past spring, as we were researching drought-tolerant garden bed design, we came across this unique "keyhole" design.  As far as we can tell from our research, it originated in drought-stricken portions of Africa, thanks in large part to humanitarian relief organizations like Send A Cow (see more in the links, below, for their wonderful keyhole-gardening educational resources.)  The keyhole design later became popular in permaculture circles here in the United States.  Keyhole gardens are fantastic for areas with drought conditions and poor soil, because they a) have a built-in composting tube in the center, b) prevent your high-quality soil from simply running off during the next deluge, and c) retain moisture due to the layering of sticks, leaves, dried grasses, and whatever else you choose to put in the bed.  

Below is a gallery of photos from the construction of our keyhole garden in March 2014.  You can read our reflections after a year of experimenting with this style garden bed here.

 

Dimensions:   Our keyhole garden measures 7 feet in diameter; the walls are about 1.5 feet tall.  The central composting tube is 3 feet tall, and 2 feet in diameter. The triangular "wedge" portion of the keyhole is 2 feet deep, and the opening widens out to 2 feet across at the mouth of the wedge.  The walls of the wedge measure 21 inches at the highest point, and taper down to 1.5 feet. (Need to convert these measurements? click here.)

Materials Needed to Build a Keyhole Garden

  • Measuring tape and twine to mark out the inner and outer circles of the keyhole garden
  • Bricks or stones to form the border
  • Chicken wire or other material to construct the central composting tube (we used 1/2 inch wire mesh), and wire to fasten it into a tube shape
  • Wire cutters
  • Material to suppress weeds (plastic sheeting/weed cloth/cardboard, etc.), as needed
  • "Wicking" materials to layer in the keyhole garden (sticks/leaves/straw/dry grass/river rock, etc.)
  • Heavy-duty cardboard, as needed
  • High-quality "fill" material to finish the keyhole garden (finished compost, manure but READ THIS FIRST, filtered topsoil)
  • Shovel, wheel barrow, and lots of helpers!

Steps

  1. Clear out any weeds or grass in the circular area where you want to build your keyhole garden.  Make sure the area will get adequate sunlight (6-8 hours), and that the ground is fairly level.  Raised bed gardens tend to settle over time, so if the area underneath isn't level, your garden may eventually resemble the Leaning Tower of Pisa!
  2. If weeds are a problem in your area, lay down a layer of weed suppressant (plastic sheeting, weed cloth, or cardboard) over the garden space.
  3. Measure out a length of twine to use as your "measuring stick."  Make two circles, either in the dirt or with a pen on your weed-suppressing material, for where you want to position your composting tube and your outer circle of bricks.  The best illustration of how to do this is in this video of Ugandan villagers building a keyhole garden (start at 00:54 on the video.) 
  4. Make a wedge-shaped notch for your "keyhole" and outline with bricks, rock or other edging material.  The purpose of the keyhole is to make it easy to reach the composting tube, so don't forget this step!  The composting tube does a fantastic job of breaking down kitchen scraps, shredded paper, leaves, sticks, etc. so you'll be adding more material to the tube daily.
  5. With wire cutters, cut down your chicken wire or other material to the size you want it, and turn it into a tube by wiring the ends together.  
  6. Make the initial outline of your keyhole garden with a single layer of bricks/stones, and place the circular tube on end in the center of the garden bed.  
  7. Begin to layer your "wicking," or water-retaining, materials in the keyhole garden.  As you can see from our photos in the gallery above, we put down a layer of crushed limestone at the base of the bed.  THIS WAS NOT A GREAT IDEA, since limestone is alkaline (as is our soil.)  We don't have any hard data to back this up, but it seemed that the addition of all this limestone didn't help our soil pH head in the right direction (a more plant-friendly 6-6.5 on the pH scale.)  A better choice, at least for our soil, would have been river rock or similar small rock, which can be purchased in bulk from landscaping companies or soil "depots."  The only downside to using crushed rock as a base is that it is labor-intensive to haul the heavy gravel around and dump it in the bed.  For this reason, we probably wouldn't put crushed rock down as a base in a keyhole garden next time.  Sticks, leaves, straw, and dried grass are all perfectly good "wicking" materials to use.  
  8. Continue to build up the side walls of the keyhole garden, layering sticks and other materials as you go.  If you need to, you can use stiff pieces of cardboard to sort of hold everything in place (see our pictures, above.)  
  9. Once the bed is built up to a height you're happy with, you can start filling it in with good-quality filtered topsoil, finished compost, and manure.  We used a combination of filtered topsoil from our local soil depot, finished compost from a garden center, and bagged turkey manure.  When it comes to selecting the right manure, read this first!  Fill the garden bed with more dirt than you might think you need, since it will settle down in the bed over time due to watering/rain/decomposition of the wood and plant fibers in the bed.)
  10. Add "compostable" materials to your central composting tube (for a list, click here!)
  11. Soak the entire keyhole garden & composting tube down with water.  And you're ready to plant!

 

Links for further research:

Send A Cow Educational Resources

                Video of Ugandan villagers building a keyhole garden--love this!
             
  PDF of How to Make a Keyhole Garden
                
PDF of What to Grow in a Keyhole Garden
                Wonderful gallery of keyhole gardens and other African drought-resistant garden techniques in Lesotho                         
                Pics of keyhole garden/mandala garden and other ideas in Uganda

Other Resources

                 Collection of various keyhole garden examples