Topsoil vs Mulch: Which to Use
Topsoil and mulch serve different purposes in the garden. Topsoil is a growing medium — plants root into it. Mulch is a surface covering — it protects the soil above the root zone. Here's how to choose.
Key Differences
| Property | Topsoil | Mulch |
|---|---|---|
| Purpose | Growing medium (roots grow in it) | Surface protection (roots grow under it) |
| Depth | 4-12" (new beds, raised beds) | 2-4" (surface layer) |
| Density | ~2,000 lb/cu yd | ~500-800 lb/cu yd |
| Composition | Mineral soil + organic matter | Bark, wood chips, leaves, straw |
| Cost | $30-50/cu yd bulk | $20-40/cu yd bulk |
| Decomposition | Doesn't decompose (permanent) | Decomposes over 1-3 years (needs replenishing) |
When to Use Topsoil
- New garden beds (need 6-12" of growing medium)
- Raised bed construction (fill with topsoil mix)
- Lawn installation (4-6" before seeding or sod)
- Leveling low spots in the yard
- Filling holes from removed tree stumps
When to Use Mulch
- Top of existing garden beds (2-3" layer)
- Around trees and shrubs (suppress weeds, retain moisture)
- Pathways (3-4" for walking surface)
- Playground surfaces (6"+ of playground mulch)
- Winter protection for tender perennials
Can You Use Both?
Yes — this is the ideal approach for new beds:
- Install 6-12" of topsoil (growing medium)
- Plant your plants
- Apply 2-3" of mulch on top (protection)
Never mix mulch into the soil as a growing medium — decomposing wood chips rob nitrogen from the soil and stunt plant growth.
Use the Calculators
- Topsoil Calculator — for growing medium volume
- Mulch Calculator — for surface protection volume