I got started on this whole Keyhole Garden thing because Deb Tolman (see some links at the bottom), a friend of mine from grad school days, is applying her Ph.D. in Environmental Science to educating folks in central Texas on how to build and maintain them. What’s a Keyhole Garden? It’s an idea that originated in some of the dustier parts of Africa, where there’s not much rainfall and the sun is a blowtorch. My working definition is that it’s a way of building and maintaining a deep soil raised bed garden in a hot, dry climate. The rest of this essay is a discussion of how you do that.
Deep soil, raised bed garden: A KHG (there, that saved eleven keystrokes) stands about two feet high or so at the outer edge, rising, volcano-like to a three-foot central peak around a composting basket. There’s a couple of advantages to this. First, that’s two feet of soil for your plants to root in, and to hold water for you. Second, that’s two feet less bending over you have to do. I was just out putting frost covers (OK, plastic bottles) on the newly transplanted tomatoes in my KHG. In my school clothes. No problem.
Building: The outer wall can be anything — field stone, cinderblock, wooden posts, water troughs, anything. A six-foot inner diameter gives something just short of eight feet outer diameter. Perfect for back yards with little space. There’s a keyhole notch cut in the wall to let you get to the central basket, of which more later.
Filling: The inner garden is six feet in diameter, which equates to about 70cubic feet of soil. The way you get that much soil is to compost it in place. Deb Tolman’s KHG DVD shows how to use 75% brown/25% green material to start a nice compost process. Brown includes cardboard boxes (liquor store), phone books (check your coat closet), old clothes (cotton or wool only), dried leaves. That gives the carbon. Green is lawn clippings, kitchen scraps (no meat or dairy), fresh tree trimmings, coffee grounds (check with your local barista — mine gives me about 10lb per week), manure. That gives you nitrogen. Layer them up in multiple thin layers, wetting them down as you go. Put some commercial potting soil on top to get started (I topped mine off with compost being sold by my local waste processing plant). Within a month or so, the stuff at the bottom will have turned into soil.*
Maintaining: There is a one foot diameter central basket made of chicken wire or a convenient equivalent, where you periodically dump kitchen scraps and lawn cuttings. As one web site said, think of it as putting your compost pile in the middle of the garden, rather than off in one corner. It’s close to the soil, because it’s surrounded by soil, and it stays moist because you are watering your garden. In fact, in many cases you will be watering your garden through the basket.
Planting: This is dense-pack planting at its finest. This spring, Debbie put seventy tomato seedlings into one garden. That gives each tomato plant an area about the size of my palm. Personally, I’m not that brave, but I do plant a lot closer than the seed packets call for. In addition, you plant shorter plants, lettuces and stuff, between the taller plants, so that they get shade. In many places the problem is how to get enough sun on your plants. In the hot and dry parts of the world, the shade helps. In last summer’s Texas Broil, the KHGs were the only thing still green.
From reading up on the KHGs, the secrets to success are (1) thin layers of well-watered 3:1 brown:green, (2) densepack plants into it the same day you are done filling it — and if you build it in a day (you know, like Rome), you can have all your greens and browns assembled and know that you’ve got the right amount of each before you start.
Next time, I’ll talk about my own personal KHG.
*The KHG pictured was a demo version, built in an Ace Hardware parking lot. A couple months later some fierce Texas t-storms washed it out. All the cardboard and phone books and branches and such had disappeared, and what washed out was pure black soil.
For more information:
Texas Co-Op Power article.
Deb Tolman talks Keyhole Gardens on central Texas NPR.
At the 9minute point. Works in the NENW as well
UPDATE: the link is restored, but it looks like the vid is gone