Keyhole Garden: Growing & Composting Combo
June 7, 2017
A drought tolerant garden is a must in places where it’s consistently hot and dry through the summer months, making a keyhole garden of huge interest to people in the southwestern US. But there are more benefits to building this kind of garden, and not having to water your veggies as often makes sense no matter how much it rains where you live. Then there’s the benefit of it creating its own organic fertilizer when built properly.
A keyhole garden is designed to include a composting tower. It was developed to enable sustainable home gardens and smallholder market farming in Lesotho, a Sub-Saharan Africa country primarily at high altitudes. A harsh climate for growing food, but keyhole gardening has made good food available to many. It works so well that the practice has spread to other parts of the African continent, and is becoming popular in arid places like Texas, California, and Colorado.
Basically, it’s a raised bed that employs permaculture practices. It must be round, have a compost bin in the center, and integrate dry organic materials as the lining of the structure. This side view cutout reminds me of chinampa construction, with its layers of compostable natural things beginning with tree parts. You will see huge keyhole gardens scattered around the internet, but they should only have about a 6-foot diameter. And there are square structures labeled the same, including prefab kits, but a true keyhole build is circular. To get a larger growing area – build more beds! It’s highly likely that the best results from the composting basket in the center rely on short distance travel of water and plant nutrients.
You can build a keyhole garden retainer walls with rocks, bricks, wood – even wine bottle cob, but according to the Engledow Group, you want them to be about 3-feet tall. Using cardboard as a liner means you don’t need to mortar your rocks together, this layer keeps both soil and moisture inside the bed. However, the cardboard will eventually rot away, so it might be a good idea to put a layer of geotextile fabric between it and your wall. Especially in a non-arid location where loss of soil due to lots of rainfall could become an issue.
The compost enclosure for recycling kitchen scraps should be 1-foot wide by 4-feet tall, made from woven wire fencing or a circle of closely set branches, and should be placed so it is totally inside the retainer walls. If the bin is half exposed it will not function properly as a composter or a source of garden moisture. Also, make sure you can reach the compost bin to add water with a watering can, and if it rains a lot where you live, you might want to add a roof over the composting space to control moisture content. This is why there’s a notch cut out of the circle.
Unlike the normal raised bed, the keyhole method requires topping off as the bottom layers decompose. Naturally, you’ll want to wait until the current crops are harvested to do so. Another important difference to note is that the soil level is higher in the center than at the walls in a keyhole planter. This allows moisture to carry the width of the planting space, distributing any rainfall and subsurface moisture to all the plants.
Before you dive into building your own, do take the time to read up on how the infill is created. It’s not going to be the same if you build a structure and fill it with potting mix or garden soil. It involves adding aged dried manure, cow bones, wood ashes, clover, rusty stuff, old compost, and forest floor mulch, along with newspaper and cardboard. All these things create naturally balanced, slow-release organic fertilizer for the plants in a keyhole garden… sustainable food production without a big price tag.
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