By Penny Pawl, U. C. Master Gardener of Napa County

I just built an African keyhole garden and I'll bet you are wondering what that is. The African keyhole garden was designed by CARE in Zimbabwe during the mid 1990s to encourage people to grow their own food. The design relied on materials that were close at hand—such as bricks, stones, branches, hay, ashes, manure and soil—to create an easy-care garden for disabled people.

The plan became so popular that many Africans began growing kitchen gardens. A so-called keyhole garden bed has a dead end opposite the opening. At the dead end is a compost bin. More than 20,000 of these have been built in Africa.

The Texas Master Gardener Association has held a number of workshops to promote this type of garden. They have also standardized the plans. Their version is a six-foot-wide garden bed with a twelve-inch-wide bin made of chicken wire in the middle. The gardener fills the bin with compostable material such as moistened newsprint, cardboard, dead plants, kitchen waste and red wiggler worms, the same components of a worm bed. The concept is that the worms will gradually decompose the material and their castings will nourish the soil and plants around the bin.

For mine, I decided to use an old garbage can with holes drilled in it. The garbage-can lid keeps out pests and any creature looking for a warm nest. I created the planting bed with building blocks set three high and cemented in place.  

Alas, I had a big problem with gophers, and I needed to win that battle. So this fall, when it was time to rework the soil, I put a layer of hardware cloth on the bottom. The hardware cloth helps to keep the gophers out. It won't last forever, but it will foil the varmints for a few years. Then a mixture of clean cardboard and soil was placed over the hardware cloth. Since the bed was already in a square keyhole shape, I added the garbage can and put soil around it to hold it in place.  

I fill this garbage can with the same things I put in my worm compost beds, including red wiggler worms. I have been watering it and feeding it for a few weeks to try to get it working. Eventually, the liquid and castings from the worms and other insects will work its way into the new bed areas and fertilize the soil from below rather than from on top.  

Tall garden beds that have compost bins built into them are called "banana circles" by permaculture specialists. I plan to incorporate banana circles in future garden beds.

When you plant your keyhole garden, aim for variety of plants in small groups as opposed to a single crop. Some vegetables do not do well in this type of situation, such as tomatoes, potatoes, peppers, eggplant, corn and squash.  

I like the concept of the keyhole garden so much—relying on a compost bin in the middle to feed the plants around it—that I plan to try it in beds without the keyhole and see what happens. These beds will need to be cleaned out and refilled every four to five years.

Keyhole gardening techniques are often used in permaculture design. For more information, consult the North Carolina State University Extension site (https://content.ces.ncsu.edu/extension-gardener-handbook/appendix-d-permaculture-design) or the Nifty Homestead site (https://www.niftyhomestead.com/blog/keyhole-garden/). You will also find more advice and books on the topic online.

Master Gardeners are volunteers who help the University of California reach the gardening public with home gardening information. U. C. Master Gardeners of Napa County ( http://ucanr.edu/ucmgnapa/) are available to answer gardening questions in person or by phone, Monday, Wednesday and Friday, 9 a.m. to Noon, at the U. C. Cooperative Extension office, 1710 Soscol Avenue, Suite 4, Napa, 707-253-4143, or from outside City of Napa toll-free at 877-279-3065. Or e-mail your garden questions by following the guidelines on our web site. Click on Napa, then on Have Garden Questions? Find us on Facebook under UC Master Gardeners of Napa County.