If you need an easy-to-reach garden bed that saves you time watering and fighting pests, look no further. The keyhole garden combines the magic of composting with the ease of raised bed gardening into one compact and productive plot.
Originally designed for growing food in Southern Africa where droughts and poor soil conditions challenge farmers, the keyhole garden is gaining traction in other parts of the world. That’s because its accessible design produces amazing results, allowing gardeners to build soil nutrition and reduce watering and fertilizer.
What is a keyhole garden?
A keyhole garden is a raised garden bed built from organic materials layered in a circle between six and eight feet wide. In the center of the circle, a composting well funnels nutrients from food waste into the nearby soil. Plant roots take up these nutrients and reward you with lush growth and an abundant harvest. You can install a keyhole garden on rocky or clay soil and still produce a bumper crop.
How does a keyhole raised bed work?
Let’s take a closer look at what’s really going on inside a keyhole garden. When examined in a cross section, a keyhole garden features four main parts.
- A drainage layer made from rocks and twigs.
- Layers of brown and green organic material balanced to rot over time.
- A layer of topsoil for planting vegetables.
- A compost well where you can add food waste and grey water (water previously used for household purposes).
A notch into the center of the bed’s circle gives the bed a keyhole shape when viewed from above. The notch helps you reach the central compost and the inner parts of the bed without straining.
Source: Fix.com Blog
What's special about the keyhole garden design?
All those layers of organic matter work together to hold in moisture. This helps minimize the amount of water you’ll need to add during the growing season. Over time, the organic layers rot to further feed the soil.
The compost well at the center of the design provides a one-stop location for kitchen scraps that immediately benefit the garden beds. In some locations, people also use the compost for disposing of grey water.
Overall, the keyhole garden is a low maintenance, high nutrient option for raised gardening at home.
Where to put your raised keyhole garden
Before you build a keyhole garden, think carefully about your location. Most garden vegetables need more than six hours of sunlight each day. If you plan to grow leafy greens like spinach and lettuce, some dappled shade will help keep your crops cool.
How to make a keyhole garden step by step
Traditionally made from scrap materials, a keyhole garden takes several hours to build. You will need:
- Sharpened stake
- String line for marking your bed
- Retaining wall material
- Drainage material
- Small wire mesh (chicken wire or hardware cloth), cut about 4’x 2.5’
- Mulching materials
Putting it all together
- Clear and level your space.
A keyhole garden adjusts easily to some bumps and dips, so your site doesn’t need to be absolutely level. But too much elevation change can make the bed tricky to build.
- Mark out your garden’s footprint.
Drive a stake into the center of the bed. Attach a string between three and four feet long. This will be the radius of your bed. Pulling the string taut, walk around the stake and mark out the circumference of your plot.
- Place your compost basket or well in the center.
Using the wire mesh, fashion a cylinder 4’ tall x 1.5’ wide and center it in your bed. The final compost well should be at least one foot taller than the final height of your retaining wall.
- Build your retaining wall.
Use whatever material you have on hand to provide a structure for the soil. Popular choices include concrete blocks, bricks, stacked stones, pieces of corrugated metal, and wood. The retaining wall needs just enough stability to hold up your soil.
- Add the notch or ‘keyhole’.
Once your perimeter is complete, remove a two-foot section of the wall. Working perpendicular, extend your retaining wall into the center, narrowing towards the compost well to create a pie shape.
- Add drainage where needed.
Spread a thin layer of drainage materials on the bottom of the bed. This could include gravel and twigs. If your soil is well-drained, you can skip this step.
- Fill the bed with layers of organic matter.
Alternate brown and green materials to maximize composting. Grass clippings, shredded leaves, straw, and old newspapers are all good candidates.
- Top with garden soil.
This layer should be at least eight inches deep. Be sure there is a slight incline moving down from the compost well. You want your soil to be sloped gently towards the retaining wall.
- Fill your compost pile.
Add compost to the central well and soak with water.
- Plant your seeds, flowers, and starter plants.
Watch them thrive!
Keyhole gardening tips
A keyhole garden will provide your soil with all the nutrients it needs for years to come. That’s because your kitchen waste will do the fertilizing for you as you water your garden through the compost well. The organic layers beneath the topsoil will release nutrients and retain water as they decompose.
Here are some more tips to help your keyhole garden thrive:
- When you first build your garden, fill your compost well so it’s level with your bed. Water your garden by pouring water through this well. As water seeps through the compost, it will carry nutrients to your plants.
- As time goes on, add enough food scraps to keep the waste in your compost pile level with your soil.
- To cut down on weeding, add mulch to the top layer of your soil, around the base of your plants. Mulch stops new weed seeds from reaching the soil and prevents older weed seeds from germinating.
- In your bed’s first year, plant crops that don’t need a great deal of soil depth. As the organic matter in your bed decomposes, your bed will be able to support more deeply rooted crops.
- Rotate the crops planted in your bed from one year to the next. Some plants carry pests and diseases that may strike similar plants in subsequent years.
- Avoid placing your keyhole garden too close to large trees. Tree roots will be drawn to the area due to the nutrients and moisture. If possible, locate your keyhole garden in an area without trees nearby.
Sustainable gardening for the long term
Whether you live in an area that experiences droughts or a place where nutrient-rich soil is in short supply, a raised keyhole garden can help address the issues that might prevent your garden from thriving. For growing vegetables or disposing of vegetable scraps, a keyhole garden can be a great addition to your landscape design.