Blocks Needed
58
Soil
79.5 ft³
Basket
5.3 ft³
Plant Area
21 ft²
Typical: 5–8 ft
Typical: 1–2 ft
Blocks Needed
58
6 ft keyhole garden
Soil
79.5 ft³
Plant Area
21 ft²
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Result
Circumference = pi × 6 - 2 = 16.8 ft. Wall area = 16.8 × 3 = 50.5 ft². Block face = 1.33 × 0.67 = 0.89 ft². Blocks = 50.5/0.89 ≈ 57.
Inputs
Result
Circumference = pi × 8 - 2 = 23.1 ft. Wall area = 23.1 × 3 = 69.4 ft². Block face = 0.89 ft². Blocks = 69.4/0.89 ≈ 78.
Standard keyhole gardens are 6 ft in diameter and 3 ft tall. This size allows you to reach the center from any point along the edge without stepping into the bed. Smaller 5 ft gardens work for tight spaces, while 8 ft gardens maximize growing area.
The compost basket is a wire cylinder at the center of the keyhole garden where you add kitchen scraps. Water poured through the basket carries nutrients outward through the soil to plant roots. A 1.5 ft diameter basket is standard for a 6 ft garden.
Cinder blocks (8×8×16 inches) are the most common choice. For a 6 ft diameter, 3 ft tall garden, you need about 50–70 blocks. Natural stone, brick, or even recycled materials like bottles filled with dirt work as alternatives.
Keyhole gardens excel with heavy-feeding vegetables like tomatoes, peppers, squash, and leafy greens because the compost basket continuously feeds the soil. Plant tall crops on the north side to avoid shading shorter plants. Herbs thrive on the edges.
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Last Updated: Mar 19, 2026
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