Small Scale Farming for Your Backyard: The Keyhole Bed

Sometimes a garden is not in the works for a homeowner. Whether gardening deters you because of time, effort, cost, or the health of your soil, keyhole beds could be the garden solution to your woes.

What is a keyhole bed?

 Keyhole beds are planters with a compost bin at the center. There are many ways to design your keyhole bed, though it is typically a circular design. A pie slice of the circular bed is removed for easy access to the compost bin. So from the top view, it looks like a keyhole. 

The design of these planters originates in sub-Saharan Africa where charitable groups utilized them to help residents of arid, malnourished land. It allowed people to grow food for their families using less water and took advantage of easily found compostable materials. 

Keyhole beds are simple to construct and deconstruct, and can be made of almost any building material. For example, the outside wall of the keyhole bed can be constructed of materials like wood, stone, cinderblock, wattle, and daub, etc. (If you do use wood, make sure you choose the right wood.) Some even advocate reusing old tires to create the edges of your bed. The use of tires in the garden is still hotly debated, however, as they can be unhealthy for the soil—and hence whatever food you are growing. 

At the core of the design is the compost bin. The mesh, cylindrical shape of the container allows nutrients to leach out into nearby garden soil. Even a chicken wire cylinder can be enough to keep your compost centralized. 

How do I build a keyhole bed?

To begin building your keyhole bed, you first want to observe your site and acquire the necessary materials. When you design the bed, the composting bin at the center should be roughly one foot higher than the exterior wall. This will cast a shadow across the garden as the sun moves through the day. To maximize sunlight to the plants, place the compost access path facing away from the sun (the sun shines from the south if you’re north of the equator).

After you have found a space with ample sunlight and enough room to fit the six-foot diameter of the planter, you’re ready to begin. The compost bin at the center should measure roughly a foot in diameter and marks the core of the design. From the center of this, measure out about three feet in all directions. This will be your outer wall. Try not to make the diameter larger than six feet, for two reasons. First, the outside plants won’t receive enough of the nutrient-rich leachate from the compost. Second, the inside plants will be too difficult to reach and harvest. 

The base of the compost bin is typically lined with rocks to aid in drainage. In this layer, you can use broken tiles, pots, twigs, and even branches. This first layer of twigs, sticks, and hardy debris continues into the base of the planting area. Ideally, as you prepare the planting area, the soil is sloped away from the compost core, enabling water and nutrients to flow out and reach the outer edges.

With the compost bin set, the outer walls built, and the initial layer laid, you can now begin to layer the soil of your planting area. You will want to build in layers of soil, manure, ash, and other organic matter. If you need to add extra structure to your keyhole bed, you can add additional layers of twigs and sticks around the planting area. This method of layering is often referred to as “lasagna mulching” because of the many layers of compostable materials. 

The planting bed layers will gradually decompose over time. As they begin to shrink, you can top them up with another layer of lasagna mulching. So as not to interfere with the crops, wait until you are finished harvesting for the year to add more mulch.

How does the keyhole bed work?

The keyhole bed has many benefits from its design. First, the compost bin provides essential nutrients to the bed. As you build your compost heap, the plant material breaks down, releasing the nutrients to the surrounding soil. Dr. Deb Tolman, who has years of experience building keyhole beds in Texas, recommends using a compost core ratio of 3:1 carbon-rich brown compostable materials to nutrient-rich green material. Examples of “brown” compostable materials include leaves and wood chips. Nutrient-rich “green” material includes kitchen scraps like peelings from fruits and vegetables and grass clippings.

These resources can be gathered from your home and garden to fill the bin, which also reduces your home’s trash going to the landfill. You can then add water the center basket, creating a compost tea as it filters through, taking water-soluble nutrients to the roots. This method of small-scale farming demonstrates that even on the most malnourished property, a properly made garden can become an oasis of life. Just be sure to keep filling the compost bin at the center of the bed!

Since the keyhole bed was designed for arid regions, it is inherently more drought tolerant. The wooden debris lining the bottom helps absorb moisture. By placing a thick layer of mulch on top of the soil, you can further add to your water retention. In particularly hot climates, construct a shade to protect the top of the compost basket. By blocking the direct sunlight and intense heat, you prevent the drying of your compost.

Why build a keyhole bed?

Since keyhole beds can be made of many different materials, whether purchased or salvaged, it makes them an affordable option for any home. And though most designs are a horseshoe shape with an edge for easy access to the compost bin, you can modify them to fit your specific needs.

They can be built as a permanent feature on your property, specially designed to be an aesthetically pleasing addition beside the kitchen. Keyhole beds can also be temporary, easy to disassemble and move if you are keen to fill a spot with food until you’re ready to build that add-on.

Also, having your plants raised above the ground alleviates back strain of harvesting. You cut down on how far you have to bend to reach the plants, making maintenance easier. And by planting strategically, placing climbing vines against the compost bin, trailing vines on the edges, and an assortment of beneficial plants in between, you are creating a diverse habitat and beautiful centerpiece.

Bottom Line

Creating features like the keyhole bed take advantage of a piece of land that may otherwise be left fallow and use recycled materials to produce a crop. When we add this into our yard, we are reducing the amount of organic waste, such as table scraps, lawn clippings, and other compost, that would end up in the garbage. We are then turning this waste into nutrients that fuel a planting area that can provide food for your family or generate happiness from the beauty of its assortment of flowers.

As Farrah Schwab explains in Permaculture News: keyhole beds are a “climate-savvy, space-saving, nutrient-recycling and waste-upcycling method.” So if you did not know about them, you might want to start making plans for next year’s garden!

Article by:

Tanner Sagouspe

Tanner Sagouspe has a Masters in Environmental Management and is a Permaculture Designer who promotes tackling the climate crisis at home.