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.
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.