The short answer
Yes. Raised bed soil can stay; it just needs topping up as it settles and breaks down. Add an inch or two of compost each year. On a 4 × 8 ft bed, 2 inches is 5.33 cubic feet, about 4 bags of 1.5 cubic feet.
How much to add
The University of Maryland Extension says just 1 inch of compost a year can help keep a garden productive. The University of Illinois Extension says a few inches of compost or good topsoil should keep up with settling. NC State Extension’s handbook says raised beds need a 1- to 4-inch layer of organic material after each season, and Washington State University Extension says to replenish beds every year or two to keep their depth.
Measure how far the soil has dropped below where you want it and enter that as the depth in the compost calculator, using the inside size of the bed.
Compost calculator
Open the calculatorDo not overdo the compost
The University of Minnesota Extension warns that regular, heavy applications of compost can build up phosphorus and salts, which can burn seedling roots. Texas A&M AgriLife Extension says not to add more than a 4-inch layer of organic material.
When to replace it
If the soil has serious problems, such as compaction or a soil-borne disease, NC State Extension says the best course may be to remove the old material and refill with a good planter mix. The soil calculator works out the full refill.
References
- Organic Matter and Soil Amendments, University of Maryland Extension
- Refreshing raised bed soil generates exceptional results, University of Illinois Extension
- 16. Vegetable Gardening (Extension Gardener Handbook, AG-831), NC State Extension
- Raised Beds: Will They Benefit Your Vegetable Garden? (FS075E), Washington State University Extension
- Raised bed gardens, University of Minnesota Extension
- Soil Preparation, Texas A&M AgriLife Extension
- Soil, Plots, and Planters (AG-806), NC State Extension