Compost vs River Rock: Size, Cost, and Which to Use

Compost

Decomposed organic matter used as a soil amendment to improve soil structure, fertility, and water retention. Quality compost is dark, crumbly, and earthy-smelling. It adds beneficial microorganisms and nutrients that support healthy plant growth and improve poor soils.

River Rock

River rock is naturally rounded stone from river beds and glacial gravel deposits, washed and screened into size bands from 3/4 inch to 8 inches. It costs $40 to $100 per ton in 2026, weighs 1.35 to 1.6 tons per cubic yard, and is the go-to decorative stone for dry creek beds, garden beds, borders, and drainage swales where the rock needs to look good and stay put. It costs two to three times what crushed stone costs because it is sorted and washed, and because the supply is limited to places with river gravel.

Compost

• ✓ Soil amendment
• ✓ Garden beds
• ✓ Lawn top-dressing
• ✓ Raised beds
• ✓ Tree and shrub planting
• ✓ Seed starting mix

River Rock

• ✓ Landscaping
• ✓ Dry creek beds
• ✓ Decorative borders
• ✓ Drainage swales
• ✓ Water features
• ✓ Ground cover

Compost

• + Dramatically improves soil structure and fertility
• + Increases water retention in sandy soils
• + Improves drainage in clay soils
• + Adds beneficial microorganisms
• + Reduces need for chemical fertilizers

• − Quality and composition vary widely between sources
• − Can be odorous when fresh
• − May contain weed seeds if not fully composted
• − Too rich for direct planting — must be mixed with soil
• − Settles significantly after application

River Rock

• + Best-looking bulk stone, natural mixed colors
• + Never decomposes, one-time install
• + Drains fast and rarely clogs
• + Large sizes stay put in moving water
• + Available in sizes from 3/4 inch to 8 inch cobbles

• − Expensive, $40 to $100 per ton
• − Never packs, so it is a poor surface to walk or drive on
• − Heavy and awkward to spread
• − Holds heat in full sun
• − Hard to clean leaves and debris out of

Compost

Fine, crumbly texture when fully decomposed. Dark brown to black color. Should smell earthy, not sour or ammonia-like. Screened compost has been filtered to remove large uncomposted pieces. Mushroom compost is a byproduct of mushroom farming and is particularly nutrient-rich.

River Rock

River rock is sold by size band: 3/4 to 1 inch (sometimes called large pea gravel), 1 to 2 inch (egg rock), 2 to 3 inch, 3 to 5 inch, and 5 to 8 inch cobbles. Every piece is smooth and rounded. Colors are a natural mix of tan, brown, gray, cream, rust, and black, with regional loads that run mostly one shade. Single-color sorted rock costs more.