Raised bed soil: getting the mix right
Last reviewed September 2026 · written from public-domain USDA/NOAA data and Cooperative Extension references — see how we source data
A raised bed is only as good as what goes in it. The goal is a mix that holds moisture and nutrients but still drains, and that you top up with organic matter every season.
A reliable fill
For most gardeners: roughly half a bulk "garden soil" or "raised bed" blend and half compost, mixed. The square-foot method's equal thirds of compost, coir or peat, and vermiculite also works well and is lighter.
Avoid filling with bagged potting mix alone (expensive, dries fast) or with native soil alone if it is heavy clay (compacts). Never use pure topsoil.
How much you need
Volume in cubic feet = length (ft) × width (ft) × depth (inches) ÷ 12. Divide by 27 for cubic yards, which is how bulk material is sold and delivered. Anything over about one cubic yard is usually cheaper delivered in bulk than in bags. The raised bed soil calculator does this and estimates bag counts.
Filling deep beds cheaply
For beds deeper than about 12 inches, the bottom third can be coarse organic matter — small logs, branches, leaves, straw — with the growing mix on top. It breaks down over a few years, feeding the bed, and you top up as it settles.
Keeping it good
Soil in a bed loses volume and fertility as organic matter breaks down and crops remove nutrients. Add an inch or two of compost each season, keep the surface mulched or planted, and avoid compacting it by never standing on the bed.