Creating Well-Draining Soil for a Raised Perennial Bed

You’re building a raised bed for perennials and small shrubs and want to know how deep to make it and what soil mix will provide excellent drainage.

Bed Depth

Most perennial roots concentrate in the top 4 inches. Add 8–10 inches of new soil; that’s sufficient for perennials and small shrubs. For larger shrubs, you can dig into the native soil and blend.

Recommended Soil Mix (by volume)

• 30% clay (for water and nutrient retention)
• 10% coarse sand (play sand)
• 40% finely ground pine bark
• 20% composted organic matter (manure, cotton burr, leaf mold, humus, or a blend)

Clay is valuable—it holds moisture and nutrients through winter and summer. Omitting it makes the bed dry out too fast.

Sourcing Materials

• Clay: Ask local builders or bulk soil suppliers; pool companies often have excess.
• Pine bark, cotton burr, leaf mold, humus: Garden centers (bagged) or bulk mulch/soil yards.
• Your composted oak/maple leaves: Excellent leaf mold—use them.
• Bagged topsoil/compost: Variable composition; mostly bark and sand. Acceptable for texture.

pH Considerations

Test the blended mix. Most perennials thrive at pH 6–6.5; acid-lovers like hollies and azaleas prefer 5–5.5. Adjust with lime or sulfur as needed.