Soil Amendment Calculator
By Amendment Type
Calculate amendment amount for your garden
Soil Problem Solver
Get amendment recommendations based on soil problems
Formula
Volume (cu yd) = Area (sq ft) × Depth (inches) / 12 / 27 | Weight = Volume (cu ft) × Weight per cu ft
Frequently Asked Questions
How much compost should I add to my garden?
Add 2-3 inches of compost annually and work it into the top 6-8 inches of soil. For new beds, add 4-6 inches. This equals about 0.6-0.9 cubic yards per 100 sq ft at 2-3 inch depth.
How do I fix clay soil?
Add 3-4 inches of compost plus 50 lbs of gypsum per 1000 sq ft, worked into the top 8-12 inches. Repeat annually for 2-3 years. Do not add sand to clay without compost - it can create a concrete-like soil. Gypsum helps break up clay particles.
When should I amend garden soil?
Fall is the best time to amend soil - amendments have winter to break down and integrate. Early spring (2-4 weeks before planting) is the second best time. Topdressing with compost can be done anytime during the growing season.
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