A keyhole garden is a raised, circular bed with a wedge-shaped path cut into it — the keyhole — that lets the gardener reach the centre without stepping on the soil, and a compost basket in the middle that feeds and waters the bed from the inside. It was developed for dry regions where water is scarce and soil is poor, and it is now used by gardeners everywhere who want a productive, water-efficient bed that is easy to reach. A keyhole garden is especially useful for gardeners who find bending difficult, because the bed is built up to waist height and every plant is within arm's reach. This guide explains how to build one, how to plant and water it, and where it works best.
The design is simple and clever. The bed is a circle, usually about two metres across, built up with stones, bricks, timber or other material to about waist height. A notch cut into the circle — the keyhole — lets you step into the centre, so you can reach every part of the bed without walking on the soil. In the middle of the bed is a compost basket, made from wire mesh or sticks, open at the top and reaching down to the ground. Kitchen scraps, leaves and other compostable material go into the basket, where they break down and feed the soil around them, and water poured into the basket soaks outwards into the bed, watering it from the inside. The bed itself is filled with layers of cardboard, manure, compost and topsoil, in the same way as a lasagne bed or a raised bed. Our raised bed gardening guide covers raised beds in general, and composting basics covers making compost.
Building a keyhole garden step by step
First, choose a site. A keyhole garden needs a sunny, level spot with room for a circle about two metres across, plus space to walk around it. It suits a garden with poor soil, because the bed is built up from imported material, and a dry garden, because the central basket waters the bed efficiently. Mark the circle on the ground, and mark the keyhole — a wedge about 60 centimetres wide at the outer edge, narrowing towards the centre, where you will stand to reach the bed.
Second, build the wall. Lay the wall material — stones, bricks, blocks, timber or even bottles packed with soil — in a circle, leaving the keyhole open, and build it up to about waist height, or lower if you prefer to sit while you garden. The wall should be sturdy, because it holds back a large volume of wet soil, and it should be built on level ground so it does not lean. If you use timber, use untreated wood, and expect it to need replacing after several years; stone and brick last longer but cost more and take more work to build.
Third, build the compost basket. In the centre of the circle, make a cylinder of wire mesh or sticks about 30 to 40 centimetres across and as tall as the bed, open at the top and reaching down to the ground. The basket should be in the middle of the bed, with the keyhole giving you access to it, so you can add scraps and water without reaching across the plants. Fill the bottom of the basket with twigs and coarse material, so air can circulate and water can drain.
Fourth, fill the bed. Lay cardboard on the ground inside the wall to suppress weeds, then add layers: coarse woody material at the bottom, then manure, then compost, then topsoil, watering each layer as you go. The finished bed should be level with the top of the wall, with the soil a few centimetres below the rim so water does not run off. Let the bed settle for a week or two before planting, and top it up with soil where it has sunk.
Planting and watering a keyhole garden
Plant the bed as you would a raised bed, with the tallest plants in the centre and shorter ones around the edge, so nothing shades its neighbours. A keyhole garden suits salad leaves, herbs, radishes, beans, tomatoes, peppers and flowers, because they are productive in a small space and they are easy to reach and pick from the keyhole. Our guides for growing lettuce, growing tomatoes and growing basil give crop-by-crop detail. Sow a little and often, so the bed is productive all season, and rotate crops each year so the same crop does not grow in the same place.
Watering is where a keyhole garden is different. Pour water into the central compost basket, and it soaks outwards into the soil, watering the bed from the inside and carrying nutrients from the compost with it. Water the surface as well in dry weather, especially for young seedlings, but the basket is the main watering route. Add kitchen scraps, leaves, grass clippings and other compostable material to the basket regularly, in small amounts, and cover each addition with a handful of dry leaves or soil to keep flies away. Do not put meat, dairy, cooked food or diseased plants in the basket, because they attract pests and can carry disease. The compost in the basket breaks down over time and feeds the bed, so a keyhole garden needs less added fertiliser than a standard bed. If you are unsure what will grow in a keyhole garden in your area, check your local extension service for advice.
Who a keyhole garden suits
A keyhole garden suits gardeners who want a productive bed in a small space, gardeners in dry areas who want to save water, and gardeners who find bending or kneeling difficult, because the bed is waist high and every plant is within reach from the keyhole. It suits a household that produces kitchen scraps, because the central basket turns them into food for the bed. It is less suited to a garden where space is very tight, because a circular bed wastes the corners of a rectangular plot, and it is less suited to large crops such as sweetcorn and pumpkins, which need more room than a keyhole bed gives. It is also a permanent structure: once it is built, it is hard to move, so choose the site carefully. Our gardening for seniors guide covers gardening at a comfortable height in more detail, and small space gardening covers making the most of a small plot.
Common mistakes
The most common keyhole garden mistakes are building the bed too small, so the soil dries out and the plants are crowded; building the wall too weak, so it bulges or collapses under the weight of wet soil; putting the wrong things in the compost basket, such as meat or diseased plants; watering only the surface and never using the basket; and planting tall crops around the edge where they shade the rest of the bed. Another is building the bed in shade, where it will never warm up and the plants will struggle. The fixes are simple: build the bed about two metres across and waist high, build the wall sturdily, put only compostable plant material in the basket, water through the basket, plant tall crops in the centre, and site the bed in sun. A keyhole garden that is built well and tended regularly will produce a surprising amount of food from a small circle of ground.
Frequently asked questions
What is a keyhole garden?
A keyhole garden is a raised, circular bed with a wedge-shaped path — the keyhole — cut into it, so the gardener can reach the centre without stepping on the soil, and a compost basket in the middle that feeds and waters the bed from the inside. It was developed for dry regions with poor soil, and it is now used by gardeners everywhere.
What do you put in the compost basket?
Kitchen scraps such as vegetable peelings, fruit cores and coffee grounds, plus leaves, grass clippings and other compostable plant material, in small amounts. Cover each addition with dry leaves or soil. Do not put meat, dairy, cooked food or diseased plants in the basket.
How do you water a keyhole garden?
Pour water into the central compost basket, and it soaks outwards into the soil, watering the bed from the inside and carrying nutrients from the compost with it. Water the surface as well in dry weather, especially for young seedlings, but the basket is the main watering route.
How big should a keyhole garden be?
About two metres across and about waist high is the usual size, with a keyhole wedge about 60 centimetres wide at the outer edge. That size lets an adult reach every plant from the keyhole or from outside the bed, without stepping on the soil. A smaller bed dries out faster and holds fewer plants.
Is a keyhole garden good for seniors or gardeners with limited mobility?
Yes, it is one of the best designs for gardeners who find bending or kneeling difficult, because the bed is waist high and every plant is within arm's reach from the keyhole. It can also be built lower, so it can be worked from a chair or a garden seat.