How to Make a Keyhole Garden

Save space and integrate your compost pile with this unique garden design.

A keyhole garden nestled against a wall
A keyhole garden can be nearly any shape and go nearly anywhere.

VLCinéaste / Flickr / CC BY-SA 2.0

Overview
  • Working Time: 6 hours
  • Total Time: 2 days
  • Skill Level: Intermediate
  • Estimated Cost: $50-75

A keyhole garden is a type of garden bed with an integrated compost bin. It was originally developed in the southern African nation of Lesotho during the drought-stricken 1990s in order to improve the soil and retain water. It then spread to other arid parts of Africa and the world, including the United States, but it's a garden design that can be used anywhere. It's not only a sustainable form of permaculture; it's a space-saving garden design requiring minimal bending or stooping.

Why It Works

Imagine a thigh-high dirt circle roughly six feet in diameter with a single narrow slice cut from it and a hole in the middle. The easily accessed hole in the middle is filled with compost and household grey water (from washing and bathing), which then feeds and waters the surrounding plants.

The raised bed can be any shape or size, making it adaptable to a variety of usable spaces. It doesn't even need to be circular, but a circular structure maximizes the amount of space you can use that's within easy reach of the center. The key to the shape is, well, the keyhole, which gives gardeners easy access to the compost pile and to nearly any point in the garden. Since the garden itself is usually raised from the underlying surface, it's well suited for places where the usable soil is non-existent, limited, contaminated, or otherwise not suitable for gardening—especially when you are growing food.

Benefits of a Keyhole Garden

Keyhole gardens thus solve a number of problems. An integrated compost pile reduces the amount of food waste sent to landfills. One-third of all food goes uneaten in the United States, and food waste is the single largest contributor to landfills. Decaying food waste in landfills produces methane, a greenhouse gas far more potent than carbon dioxide. One report from the Intergovernmental Panel on Climate Change estimates that between 8 and 10% of greenhouse gas emissions produced between 2010 and 2016 came from food waste. Food rotting in the presence of oxygen does not produce methane, however, which is what differentiates a compost pile from a landfill, so if you keep your compost pile well-aerated, your food scraps won't be contributing the climate change.

Using grey water in a keyhole garden also cuts down on the depletion of freshwater reserves. According to the UN's Sustainable Development Goals, 40% of the world's population lacks access to safe and affordable drinking water. As average global temperatures rise, irrigated land dries out more quickly, wasting water, and disrupted weather patterns bring longer and more intense droughts. Even in areas not burdened by frequent droughts, groundwater is being depleted at unsustainable rates.

Finally, topsoil erosion is a growing problem not just in Africa but worldwide, where “the majority of the world's soil resources are in only fair, poor, or very poor condition,” according to the UN's Food and Agriculture Organization. In the United States, soil erosion occurs at an estimated twice the annual rate as it did during the Dust Bowl of the 1930s. With topsoil drying out more quickly from increasing average temperatures, the amount of plant and microbial life beneath the surface is reduced, increasing the potential for greater erosion.

What You'll Need

Tools

  • 1 shovel
  • 1 wheelbarrow
  • 1 trowel
  • 1 hoe
  • 1 heavy duty stapler (optional)

Materials

  • Stacked stones, cinder blocks, corrugated metal, shipping pallets cut in two, or old fencing material.
  • 5 wood stakes, 3-5' long
  • Chicken wire, hardware cloth, or other permeable material sheeting.
  • J-Clips, heavy duty staples, or bailing wire.
  • Gravel, crushed stone, or other loose material
  • Red wigglers (optional)
  • Raised bed filler (see instructions)
  • Weed block (optional)
  • Seeds or seedlings
  • 1 half yard loam soil
  • Airflow tube (optional)

Instructions

  1. Choose a Location

    Clear a level circular area roughly 6 feet in diameter.

  2. Trace the Keyhole Garden

    Stake a 3-foot string in the intended central point of your garden and trace a circle around the perimeter of your garden.

  3. Prepare to Build

    Roughly lay out your wall-building materials around the perimeter, leaving a pathway to the center of the circle. For materials, use anything that you can stack two to three feet high to create the garden's outer walls to keep in the soil without leaching anything into it. If your outer wall has gaps in it, you can line the inside of the walls with cardboard or other materials to prevent soil from escaping.

  4. Make a Compost Area

    Mark out a composting area in the center of the circle, about 18 inches in diameter.

  5. Place Stakes

    Place five wooden stakes around the perimeter of the composting area. Your raised bed can be of any height, but make the compost pile a foot or two taller than your garden walls. 

  6. Attach Chicken Wire

    Attach chicken wire to the outsides of the stakes using J-clips, heavy-duty staples, baling wire, or other materials that won't decompose or leach chemicals.

  7. Create Aeration

    For aeration, put 3-4 inches of loose gravel, stones, or broken-up shipping pallets at the bottom of your compost pin.

  8. Add Topsoil

    Place topsoil over the aeration material, then fill your compost pile with a mix of brown and green waste: grass clippings, fallen leaves, mixed in with food waste. Skip meat and dairy products if you want to avoid critters larger than worms from making a mess of your compost pile. You can also add red wigglers or earthworms to your compost pile.

    Optional: Create an airflow tube by drilling holes in repurposed drainpipe or PVC pipe every 6 inches along the length of the pipe. Insert the pipe into the compost pile to promote aeration.

    Overhead photo of a compost bin as part of a keyhole garden

    VLCinéaste / Flickr / CC BY-SA 2.0

  9. Add Water

    Periodically, add grey water to the compost pile—not directly onto your plants, which require only clean water from a tap or a rain barrel.

  10. Slope Your Garden

    Slope your garden away from the compost pile in the center so that the water and nutrients filter out into your garden. The outer edge of your garden wall should be an two inches or more lower than the outer edge of the compost pile.

  11. Build the Outer Wall

    Build the outer wall of the garden.

  12. Layer Your Garden

    Fill your garden bed with layers of materials, beginning with well-draining materials such as stone, twigs, or broken clay pots, then a layer of cardboard, newspaper, straw, wood ash, compost, topsoil, or composted cow manure, then a nutrient-rich loam soil. (Optional: Cover your soil with a weed block.)

  13. Plant Seeds After a Week

    Let the soil settle for a week before beginning planting. Plant seeds or seedlings and water in with fresh water (never grey water). Periodically add more grey water and brown and green waste to your compost pile.

View Article Sources
  1. "Food Loss and Waste." U.S. Department Of Agriculture.

  2. Food Loss and Waste.” U.S. Food & Drug Administration.

  3. "Fighting Food Waste Means Fighting Climate Change." United Nations Framework Convention On Climate Change, 2020.

  4. Composting to Avoid Methane Production.” Department of Primary Industries and Regional Development - Government of Western Australia, 2018.

  5. UN Sustainable Development Goal 6: Clean Water and Sanitation.” United Nations Development Programme.

  6. Climate Change Indicators: Drought.” U.S. Environmental Protection Agency.

  7. Famiglietti, James S., and Grant Ferguson. "The Hidden Crisis Beneath Our Feet." Science, vol. 372, no. 6540, 2021, pp. 344-345., doi:10.1126/science.abh2867

  8. Status of the World’s Soil Resources. Food and Agricultural Organization of the United Nations, Rome, 2015.

  9. DeLonge, Marcia, and Karen Perry Stillerman. "Eroding the Future." Union of Concerned Scientists, 2020.

  10. Dove, Nicholas C. et al. "Metabolic Capabilities Mute Positive Response to Direct and Indirect Impacts of Warming Throughout the Soil Profile." Nature Communications, vol. 12, no. 1, 2021, doi:10.1038/s41467-021-22408-5

  11. Borrelli, Pasquale et al. "Land Use and Climate Change Impacts on Global Soil Erosion by Water (2015-2070)." Proceedings Of The National Academy Of Sciences, vol. 117, no. 36, 2020, pp. 21994-22001., doi:10.1073/pnas.2001403117