Raised Bed Soil Depth Guide
The right soil depth depends on what you’re growing. Shallow-rooted crops like lettuce and herbs need 6 inches. Most vegetables need 8 to 12 inches. Root crops like carrots and potatoes need a full 12 inches. If your raised bed sits on top of native soil (no barrier at the bottom), roots can extend beyond the fill depth, so shallower fill works.
For beds on concrete, decks, or with a bottom barrier, fill to the full bed height. Factor in 10 to 15% settling. Soil compresses after the first few waterings, so slightly overfilling is better than underfilling.
Soil Types and When to Use Each
| Soil Type | Cost per Cubic Yard | Best For |
|---|---|---|
| Garden soil | $25 to $50 | In-ground beds, amending existing soil |
| Raised bed mix | $35 to $60 | Raised beds (blended for drainage and nutrients) |
| Potting mix | $8 to $15 per bag | Containers, indoor plants (lightweight, sterile) |
| Compost | $25 to $40 | Amending soil, top-dressing, improving structure |
| Topsoil | $15 to $30 | Filling, grading, covering large areas |
Common Raised Bed Sizes
| Bed Size | Volume at 6″ | Volume at 12″ |
|---|---|---|
| 4 x 4 ft | 8 cu ft (0.3 cu yd) | 16 cu ft (0.6 cu yd) |
| 4 x 8 ft | 16 cu ft (0.6 cu yd) | 32 cu ft (1.2 cu yd) |
| 4 x 12 ft | 24 cu ft (0.9 cu yd) | 48 cu ft (1.8 cu yd) |
| 3 x 6 ft | 9 cu ft (0.3 cu yd) | 18 cu ft (0.7 cu yd) |
