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Calculate the soil mix with amendments needed for garden beds, raised planters, and containers.
Cubic Yards = (Length × Width × Depth in feet) ÷ 27
Amendment = Total Cu Yd × (Amendment % ÷ 100)
Base Soil = Total Cu Yd - Amendment
For a 4×8 foot raised bed that is 12 inches deep: (4 × 8 × 1) ÷ 27 = 1.19 cubic yards
A 4×8 foot raised bed that is 12 inches deep needs approximately 1.19 cubic yards or 32 cubic feet of soil.
The "Mel's Mix" is popular: 1/3 compost, 1/3 peat moss or coir, 1/3 vermiculite. For larger beds, 60% topsoil + 30% compost + 10% perlite works well.
Use topsoil for filling large areas. Garden soil (amended topsoil) is better for planting as it contains added nutrients and organic matter.
Add 25-30% compost by volume for new beds. For established beds, add 1-2 inches annually. Heavy-feeding vegetables benefit from up to 50% compost.