The circle vegetable garden, also known as a keyhole bed, emerged from the permaculture gardening movement that began in Australia in the 1960s. In permaculture, gardeners work with their land to make the most of the available space, usually for food production. Circle vegetable beds represent an important aspect of this super-efficient strategy, and are easy to maintain while also adding graceful lines to your landscape.
Circle vegetable gardens maximize available growing space. Permaculture writer Toby Hemenway compares three types of vegetable gardens, each set in a 50-square-foot plot. With conventional row planting, paths between the rows hog 40 of those 50 square feet. Rectangular raised-bed gardens, although more efficient than rows, still require 10 square feet of path. The circle garden, on the other hand, narrows that gap even further, using just 6 of the garden's 50 square feet for pathways.
In addition, if the circle beds face the south and tall plants line the perimeter, the horseshow-shaped growing space creates a heat trap in the inner garden, warming the night air in the spring and fall. This practice makes it easier for northern growers to grow long-season veggies such as eggplants and peppers.
Although the geometry of the circle garden might seem self-evident, in reality the growing space is horseshoe-shaped, with a "keyhole" path -- a straight line ending in small circle -- entering from one side and ending at the center. This small inner circle allows the gardener room to turn and access any part of the horseshoe growing space from the center of garden bed.
Outline a circle 8 to 12 feet in diameter anywhere in your yard. Most vegetables require full sun, but crops like lettuce and sorrel will do well in a part-shade location. Use rope or garden lime to make the outline. At the most logical access point, outline a 1-foot path leading from the edge of the circle to the center of the circle. At the end of the path, create a smaller, inner circle about 18 to 24 inches in diameter. This will be the area from which you will be turning, squatting, bending and reaching in all directions, so don't make it any smaller than 18 inches in diameter.
Gardeners have two choices in preparing the soil in their circle beds --- digging down or building up. If you begin preparing the autumn before the actual growing season, avoid the heavy-duty spade work by laying down a weed barrier such as overlapping newspaper sections and adding layers of compost, topsoil, hay, grass and leaves on top --- a process known as sheet-composting. Make it at least 2 feet high, and by the following spring, you'll have 6 inches of rich soil in which to plant, with the ground underneath the newspaper slowly decaying and enriching itself for future years' planting.
Alternatively, break up the sod within the horseshoe part of your garden, if necessary, and dig at least a foot down. Add compost, manure and other soil-enriching additives.
Lay down a thicker weed barrier for the path section of your garden, and cover it with gravel or mulch.
In general, it's best to plant your garden in three rows. Put lower-growing, daily-gathered crops such as lettuce and herbs, in the row closest to the path --- the inner row, the one curving around the path. Set veggies like tomatoes, bush beans and peppers --- crops needing frequent but not daily tending and harvesting -- in the middle horseshoe or row. Save the one-harvest vegetables for the outer horseshoe. These are crops like cauliflower or Brussel sprouts that produce just one harvest, then must be removed.
Also devote an entire bed to one crop, such as tomatoes, with perhaps some basils or other culinary herbs in front. If space allows, use the back row to provide a windbreak and sun trap for the tomatoes by planting tall crops like sunflowers, suggests Grégoire Lamoureux, director of a permaculture institute in British Columbia.
The classic mandala garden comprises a series of circle gardens. If space allows, construct a series four to eight circle beds around a central circle bed, leaving enough space between the circles to roll a wheelbarrow or other equipment through.