How often should I replenish soil in deep raised beds?
Written by
Benjamin Miller
Reviewed by
Prof. Charles Hartman, Ph.D.Deep raised beds don't require surprising soil turnover either, due to their weight and volume. Shallow beds must be completely overhauled every 1-2 years, whereas 18" or greater beds will retain their fertility for much longer. Hefty dressings of mulch each year suit my deep beds better than a complete soil turnover. Your garden will benefit from the stable ecosystems created with less work.
Annual Top-Dressing
- Layer depth: Add 2-3 inches compost each spring
- Material choice: Well-aged manure or leaf mold works best
- Timing: Apply before planting season begins
- Benefits: Replaces nutrients without disturbing soil structure
Partial Refreshment
- Frequency: Replace top 6 inches every 3 years
- Soil mix: 60% topsoil, 30% compost, 10% perlite
- Root protection: Avoid disturbing lower root zones
- Ecosystem preservation: Maintains established microbiology
Complete Replacement
- Rare need: Only necessary every 4-5 years
- Indicators: Persistent disease or compaction issues
- Volume management: Remove soil in sections over weeks
- Amendment: Add 20% fresh compost to new soil
The meaning of less need is explained by the volume advantage. More soil means more reserves of nutrients, as well as a greater diversity of soil life. My deep beds maintain a constant nitrogen level for three consecutive years. The shallow beds exhaust their nutrients quickly and require constant renewal. Your deep bed settles down into a self-sustaining, self-repairing ecosystem.
Top-dressing is very important. Apply the compost evenly on the surface. Let earthworms mix it naturally. I do not want to till and disturb my mycorrhizal networks. Water the application well. This way, your plants get slow-release nutrients through the growing season.
Deepening the beds improves the soil's structure over time. Organic matter accumulates and forms stable aggregates. Water infiltration is improved, and erosion is decreased. Soil tests indicate that the soil texture has improved over the past 5 years. Your garden develops substantial resilience to withstand drought and heavy rain with minimal attention.
Read the full article: The Ideal Raised Bed Depth for Your Garden
