Cubic yards, bags, and cost of compost, peat, perlite, or other amendments for any garden area.
Last reviewed: April 2026
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Soil amendments (compost, peat moss, perlite, vermiculite) improve soil structure, drainage, and nutrient content. This calculator determines how many cubic yards and bags you need based on your garden area and desired amendment depth. A typical vegetable garden bed needs 2–4 inches of compost mixed into the top 6–8 inches of soil.
Compost adds nutrients and improves both drainage (in clay) and water retention (in sand). Peat moss lowers pH for acid-loving plants. Perlite improves drainage in container mixes. Vermiculite retains moisture. For raised beds, a common mix is 40% topsoil, 40% compost, 20% perlite or coarse sand. For other landscape calculations, see our Mulch Calculator and Gravel Calculator.
| Amendment | Application Rate | Purpose |
|---|---|---|
| Compost | 1–3 inches/year | Improve structure, add nutrients |
| Lime (calcium carbonate) | 25–50 lbs/1000 sq ft | Raise pH (acidic soil) |
| Sulfur | 5–10 lbs/1000 sq ft | Lower pH (alkaline soil) |
| Perlite | 10–20% of volume | Improve drainage |
| Peat moss | 1–2 inches tilled in | Retain moisture, lower pH |
Soil is composed of mineral particles (sand, silt, and clay), organic matter, water, air, and living organisms. The relative proportions of sand, silt, and clay determine soil texture, which in turn affects drainage, aeration, nutrient retention, and root penetration. Sandy soils drain quickly but hold few nutrients and dry out fast. Clay soils retain water and nutrients but drain poorly, compact easily, and can suffocate roots. Loam, the ideal garden soil, contains roughly equal proportions of sand, silt, and clay with abundant organic matter. Most natural soils are far from ideal, which is where amendments come in.
Soil amendments physically change the structure of the soil rather than simply adding nutrients (which is what fertilizers do). Compost is the most versatile amendment because it improves both extremes: it opens up clay soil by creating air pockets between particles, and it helps sandy soil retain moisture by acting like a sponge. A single inch of quality compost mixed into the top six inches of soil can increase water-holding capacity by 20 percent in sandy soils and improve drainage by 15 percent in clay soils. For calculating material volumes in other landscaping projects, see our Mulch Calculator and Gravel Calculator.
Applying amendments without a soil test is like taking medicine without a diagnosis. County extension offices across the United States offer soil testing for $15 to $30, returning results within two to four weeks. The test reveals pH (most vegetables prefer 6.0 to 7.0), macronutrient levels (nitrogen, phosphorus, potassium), micronutrient status, organic matter percentage, and cation exchange capacity (a measure of the soil's ability to hold nutrients). Based on these results, the extension service provides specific amendment recommendations for your intended crop or landscape use.
pH is the single most important soil characteristic because it controls nutrient availability. Even if nutrients are present in the soil, plants cannot absorb them outside their preferred pH range. Iron becomes unavailable above pH 7.5, causing yellowing leaves (chlorosis) in acid-loving plants like blueberries and azaleas. Phosphorus locks up in both highly acidic and highly alkaline soils. Adjusting pH takes time: garden lime (calcium carbonate) raises pH gradually over 6 to 12 months, while eleite sulfur lowers pH through bacterial oxidation, which also takes several months. Apply pH amendments in fall to allow time for reaction before spring planting.
| Soil Problem | Best Amendment | Application Rate | Frequency |
|---|---|---|---|
| Heavy clay | Compost + coarse sand | 3-4" tilled 8" deep | Annually until improved |
| Sandy, drains too fast | Compost + peat moss | 3-4" tilled 6" deep | Annually |
| Low pH (acidic) | Garden lime | 25-75 lbs/1,000 sq ft | Per soil test, every 2-3 yrs |
| High pH (alkaline) | Elemental sulfur | 5-15 lbs/1,000 sq ft | Per soil test, every 1-2 yrs |
| Compacted soil | Compost + gypsum | 2-3" compost + 20 lbs/1,000 sq ft gypsum | Annually |
| Low organic matter | Aged compost | 2-3" per year | Annually until 5%+ OM |
Raised beds and containers require entirely different soil mixes than in-ground gardens because drainage, aeration, and root space are constrained by the container walls. The most widely recommended raised bed mix is roughly 40 percent topsoil, 40 percent compost, and 20 percent coarse perlite or vermiculite. This combination provides adequate drainage while retaining sufficient moisture and nutrients. For containers, replace topsoil with peat moss or coconut coir to reduce weight: a standard container mix is one-third peat moss, one-third vermiculite, and one-third compost.
Filling raised beds is a significant material cost. A standard 4-by-8-foot raised bed that is 12 inches deep requires approximately one cubic yard of soil mix, which costs $30 to $60 for bulk delivery or $80 to $150 in bagged form. Deeper beds (18 to 24 inches) for root vegetables double the material requirement. Some gardeners use the "lasagna" or "hugelkultur" method, filling the bottom third of deep beds with logs, branches, and leaves that decompose slowly, reducing the amount of premium soil mix needed while creating a nutrient-rich growing environment over time. Calculate material quantities for larger landscaping projects with our Cubic Yards Calculator and Concrete Calculator.
Timing your amendments maximizes their effectiveness. Fall is the best time to apply lime, sulfur, and fresh compost because these amendments need months to integrate with the soil. Winter freezing and thawing cycles break down fresh compost and work amendments deeper into the soil profile. Spring applications should use only well-aged, finished compost that will not rob nitrogen from germinating seeds as it decomposes. Summer side-dressing with compost around established plants provides a slow-release nutrient boost during peak growing season. Cover crops planted in fall and tilled under in spring (green manure) add organic matter, fix nitrogen, prevent erosion, and improve soil structure at minimal cost compared to purchased amendments.
Not all compost is equal. Municipal compost programs produce large volumes at low cost ($20 to $40 per cubic yard delivered) but quality varies depending on feedstock and processing. Hot composting at temperatures above 130 degrees Fahrenheit for several weeks kills weed seeds, pathogens, and most herbicide residues. Ask your supplier about their process and request a compost analysis report showing nutrient content, pH, carbon-to-nitrogen ratio, and contaminant testing. The ideal compost for garden use has a carbon-to-nitrogen ratio of 15:1 to 25:1, pH between 6.5 and 7.5, and is dark, crumbly, and earthy-smelling with no recognizable feedstock materials.
Homemade compost from kitchen scraps and yard waste is excellent but takes 3 to 12 months to mature depending on management. Hot composting (turning frequently, maintaining moisture) produces usable compost in 6 to 8 weeks. Cold composting (passive piling) takes 6 to 12 months but requires minimal effort. Worm composting (vermicomposting) produces high-quality castings in 2 to 3 months and works well for apartment gardeners. Regardless of source, finished compost should pass the squeeze test: a handful should feel moist but not drip water when squeezed, and should hold together briefly before crumbling. For estimating material quantities across your entire landscape, use our Soil Calculator.
→ Always add 10–15% for waste. Materials get cut, broken, or mis-measured. Order extra to avoid a second trip to the supply store mid-project.
→ Measure twice, calculate once. Double-check your measurements before entering them. A small measurement error can mean ordering significantly too much or too little material.
→ Check local building codes. Requirements vary by jurisdiction. This calculator uses standard practices, but your local code may specify different minimums or methods.
→ Save your calculations. Use the share or print feature to keep a record of your material estimates for reference at the store or job site.
See also: Retaining Wall Calculator · Snow Load Calculator · Fence Calculator · Roof Pitch Calculator · Tile Calculator