Soil Amendment Calculator

How to Use This Soil Amendment Calculator

Enter your garden bed dimensions and the depth you plan to till amendments into (typically 3-6 inches). Then adjust the amendment ratio sliders to match your target mix. A common ratio for vegetable gardens is 60% compost, 20% peat moss, and 20% sand. The calculator shows cubic yards for each component.

How to Amend Garden Soil for Better Growth

Most garden soils benefit from amendments that improve texture, drainage, and organic matter content. The goal is to create loamy soil — a balanced mix of sand, silt, and clay with plenty of organic matter. Clay soils need sand and compost to improve drainage; sandy soils need compost and peat moss to retain moisture.

Common Amendment Ratios by Soil Type

• Clay soil: 30% compost, 20% peat moss, 50% coarse sand (sand opens up dense clay)
• Sandy soil: 50% compost, 30% peat moss, 20% existing sandy soil (organic matter holds water)
• New raised bed: 60% compost, 20% peat moss, 20% coarse sand (balanced mix for vegetables)
• Flower beds: 70% compost, 20% peat moss, 10% sand (more organic matter for blooms)

Amendment Tips

Add amendments in fall for spring planting — this gives organic matter time to break down. Till amendments into the top 6-8 inches where most plant roots grow. After amending, test your soil pH (most vegetables prefer 6.0-7.0). One application typically lasts 2-3 growing seasons before organic matter needs replenishing.