Chinook winds blow away wood mulch. This Alberta gardener wants decorative rock—grey limestone or black lava—for beds with tulips, lilies, hostas, and rhododendrons. Concerns: sharp edges, heat, pH effects.
| Rock | pH Effect | Heat | Sharpness | Best For |
|---|---|---|---|---|
| Limestone | Raises pH (alkaline) | Moderate | Angular, sharp | Alkaline-loving plants only |
| Black lava | Neutral | High (absorbs sun) | Porous, rough | Succulents, xeric beds |
| River rock (Alberta/Montana rainbow) | Neutral | Low (rounded, light) | Smooth | Mixed perennial beds |
| Rundle (dark grey) | Neutral | Moderate | Angular | Contrast, modern look |
Alberta/Montana rainbow river rock (2–3″) is ideal: rounded (no stem damage), neutral pH, light color reflects heat, locally sourced (Burnco, landscape centers). Keep a 3–4″ mulch-free ring around plant crowns.
Avoid limestone near rhododendrons (acid-lovers). Lava rock overheats hosta crowns. River rock is the safe, attractive, wind-proof choice.
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