Mulch is cheaper upfront and better for plant health; rock costs more on day one but almost nothing afterward. As a rule of thumb: use mulch in planting beds you tend, and rock in low-maintenance zones — borders, drainage paths, and areas where you never want to top anything up again.
Head-to-head comparison
| Wood mulch | Rock (river rock / gravel) | |
|---|---|---|
| Upfront cost per yard | $25–$50 | $50–$150 |
| Replacement | Top up yearly | Essentially never |
| Plant health | Feeds soil, holds moisture | Radiates heat, adds none |
| Weed control | Good with 3" depth | Good with fabric underneath |
| Slopes | Washes out in storms | Stays put |
| Around trees & veggies | Ideal | Avoid |
| Fire-prone areas | Combustible | Fireproof |
The 5-year math
A 200-square-foot bed at 3 inches needs about 1.85 cubic yards. With mulch at $35/yard topped up yearly, five years costs roughly $200–$300 including the initial fill. The same bed in river rock at $100/yard costs about $185 once — then nothing. Rock usually breaks even around year three, sooner if you pay for installation labor each spring. Those figures assume you know the quantities: how many bags of mulch in a yard and how much a yard of river rock weighs set the delivery cost on each side.
Where each one wins
Choose mulch for vegetable gardens, tree rings, and any bed you replant — it cools roots, feeds the soil as it breaks down, and is easy to dig through. Choose rock for drainage swales, house perimeters (termite-safe), slopes, high-wind or wildfire zones, and xeriscapes. Many yards use both: mulch inside the beds, a rock border where the lawn mower edge runs.
Get quantities for either option with our mulch calculator or river rock calculator — both convert the same bed dimensions into yards, bags, and tons.