River Rock Raised Beds: Trench Foundation, Mortar Core, Formed Face

Building 2×4×8 ft raised beds with free river rock (football to beach ball size). Round rock won't dry-stack stably. Best method:

Recommended: Formed Face + Mortar Core

1. Dig shallow trench for first course.
2. Plywood forms (rectangles for length/width).
3. Place rocks flat against form interior.
4. Pour cement/rubble mix behind rocks (1 cement : 3 sand).
5. Work up to top; cap with rocks when cement firms.
6. Remove forms → rock-faced wall with solid core.

Mortar Mix

• Pre-mixed Portland (add water) OR batch: 1 Portland : 3 cement sand.
• Mix in plastic wheelbarrow with flat hoe → thick pea soup consistency.
• Let slake 5 min before use.

Cement Safety

• Not toxic to plants (confirmed by organic cert testing).
• Only edge effect: faster drying near wall.

Alternative

If rocks are flat-sided: dry-stack with cement rubble behind for stability, 6–8" wide flat top for sitting.

Resource

Rock wall examples: avant-gardening.com (virtual tours).