How much compost for a 100 sq ft vegetable garden?

Two inches is a moderate amount for a vegetable plot on tired but workable soil. Oregon State University Extension suggests more, 3–4 in, when building a new bed on poor ground, and 1/4–1 in a year once a bed is established, so this figure sits between the two.

What to know about compost for a 100 sq ft vegetable garden

A hundred square feet is a 10 × 10 plot, but it is also almost exactly three 4 × 8 raised beds (96 sq ft of soil surface). So the same 17 bags would give three beds a generous 2 inch top-up, and half of it covers the yearly inch that keeps them full as the organic matter breaks down. For filling a new bed rather than topping one up, see How much soil for a 4×8 raised bed.

Mix it in, don’t just lay it on top. Oregon State suggests working compost into the top 8–12 in of soil for a new bed. A spading fork or a broadfork does this in an afternoon at this size; a tiller is optional.

At about two-thirds of a cubic yard, you are in the awkward zone for buying. Many landscape yards sell a half-yard minimum, which would be not quite enough, and a full yard leaves some over for next spring. Seventeen bags is a lot of plastic but only one or two car trips. Some towns give away or sell municipal compost cheaply; check whether it is screened.

Watch the long run. Year after year of heavy compost can load the soil with phosphorus and salts. A soil test every few years tells you when to drop to a thinner layer.

Building the bed up with soil as well? How much topsoil for a 10×10 garden bed covers the same footprint 6 inches deep. For lawns, where compost goes on far thinner, see How much compost to topdress 1,000 sq ft of lawn.