GROWING GUIDE
What Is Organic Matter in Soil?
Soil organic matter is living, dead, and decomposing plants, animals, and microbes in the soil. Finished compost is one way to add it, not a synonym for it. University of Maryland Extension says most landscape plants do best at at least 2% organic matter by weight, and vegetable and flower beds should aim for 5% to 10%.
Choose the amendment from a measured organic-matter level, not from a picture of dark soil. University of Maryland Extension defines organic matter as living, dead, and decomposing material, and says most garden and landscape plants perform best at a level of at least 2% by weight. The goal for vegetable and flower beds is 5% to 10%. That percentage is the same target on sand, loam, and clay. Texture changes the method. Sandy beds lose organic matter faster, so plan on about 1 inch of compost a year to hold the level. A new clay bed, or a bed with thin topsoil, can take 2 to 4 inches of compost worked into the top, not a pot filled with compost alone. One inch over 100 square feet is about 8.33 cubic feet of compost. Peat is the amendment to skip when compost or pine bark fines will do the job. A soil test is the number. This page only tells you whether you are building toward 5% or maintaining it.
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What organic matter percentage should I aim for?
Amendment choice: if a soil test is under 2% organic matter, add compost (or pine bark fines instead of peat) and test again later. If a vegetable or flower bed is already at 5% to 10%, maintain it with about 1 inch of compost a year instead of burying a thick new layer.
| Texture | OM% by weight | What to do |
|---|---|---|
| Sand | At least 2% landscape; 5–10% in vegetable and flower beds | Organic matter breaks down faster. Plan on about 1 inch of compost a year. |
| Loam | At least 2% landscape; 5–10% in vegetable and flower beds | 1 inch of compost a year maintains many beds. 8.33 cubic feet covers 100 square feet at 1 inch. |
| Clay or thin topsoil | At least 2% landscape; 5–10% in vegetable and flower beds | On a new bed, work in 2 to 4 inches of compost. Do not fill the bed with compost alone. |
Make the compost with how to compost at home or the browns and greens pile. Measure a new raised bed with the soil calculator before you buy the cubic feet. Tomatoes that will use the bed are in how to grow tomatoes.
Common questions
What organic matter percentage should I aim for?+
Maryland Extension says most landscape plants do best at at least 2% organic matter by weight. Vegetable and flower beds should aim for 5% to 10%. A lab test reports the percentage. A dark color does not.
Is compost the same as organic matter?+
No. Compost is an amendment you add. Organic matter is what is already in the soil, including living roots and microbes. Finished compost raises organic matter. It is not the whole measurement.
Does sand need a different percentage than clay?+
Use the same 5% to 10% bed goal. Sandy soil loses organic matter faster, so the yearly 1-inch compost top-up matters more. A new clay bed can take 2 to 4 inches worked into the top.
Should I add peat?+
Maryland Extension points to compost and pine bark fines as peat substitutes. Choose compost when the goal is organic matter. Use the raised-bed calculator if you need the volume of a 1-inch layer.
Sources & editorial notes
Sources checked November 4, 2026. Compiled with AI assistance from the linked pages. This is not a Plant Care Steps growing trial. Editorial responsibility.