The short answer
A raised bed on open ground takes a mix of topsoil and compost. Pots take potting mix. Compost is an ingredient, not a fill on its own. Read the bag: a product called “garden soil” or “organic soil” may contain little or no mineral soil.
What each one is
| Product | What it is | Use it for |
|---|---|---|
| Topsoil | The upper layer of soil: broken-down organic matter mixed with mineral soil (clay, silt and sand), in the University of Maryland Extension’s definition | The mineral part of a raised bed mix, a new lawn, leveling |
| “Garden soil” and “organic soil” bags | Often no mineral soil at all: the University of Maryland Extension says bags sold as organic soil typically contain no topsoil | Check the ingredients before using it as topsoil |
| Bulk “topsoil” from a yard | Often landscaping fill, a mix of sand and compost, according to Washington State University Extension | Ask for the mix and a soil test before you buy |
| Potting mix or potting soil | A light mix for containers | Pots and seedlings; the University of Minnesota Extension says it dries out too quickly in raised beds |
| Compost | Broken-down organic matter | Mixing into beds and topping up each year; NC State Extension advises against filling a planter with compost alone |
Which one for your job
A raised bed: topsoil plus compost, from two parts to one up to equal parts; the recipes guide compares the published mixes and the soil mix calculator counts the bags. A bed on paving: compost with a soilless mix, as the University of Maryland Extension gives for hard surfaces. A pot: potting mix; the pot size pages give quarts and cubic feet. A lawn or a low spot: topsoil, measured with the topsoil calculator. A yearly top-up: compost, with the compost calculator.
Raised bed soil mix calculator
Open the calculatorBefore you buy topsoil in bulk
Topsoil sales are not regulated in Maryland, and the University of Maryland Extension suggests asking a nursery or topsoil dealer for soil test results. Its guide describes good topsoil as dark and crumbly with an earthy smell, and says not to buy soil that is very high in sand or clay, smells foul, or has grayish mottling or a chalky, sticky or rough texture. The bulk buying guide covers delivery and the other checks.
References
- Growing Vegetables in Raised Beds, University of Maryland Extension
- Organic Matter and Soil Amendments, University of Maryland Extension
- Raised Beds: Will They Benefit Your Vegetable Garden? (FS075E), Washington State University Extension
- Raised bed gardens, University of Minnesota Extension
- Soil, Plots, and Planters (AG-806), NC State Extension