What Soil to Fill a Raised Bed With
Use about 1/2 to 2/3 loam or sandy loam topsoil and 1/3 to 1/2 plant-based compost. Do not fill a bed with potting soil, and go easy on manure. Equal part...
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What Soil to Fill a Raised Bed With
Fill it with about 1/2 to 2/3 topsoil and 1/3 to 1/2 plant-based compost. That is the mix University of Minnesota Extension recommends. Pick loam or sandy loam topsoil. Skip very sandy or heavy clay soil.
The Raised Bed Desk splits your total into each ingredient in cubic feet, cubic yards, and bags.
Three Mixes That Work
| Mix | Recipe | Notes |
|---|---|---|
| Topsoil and compost | 60% topsoil, 40% compost | Holds water well. Cheapest in bulk. |
| Equal thirds | 1 part topsoil, 1 part compost, 1 part coarse sand, perlite, pumice, or vermiculite | From Utah State University Extension. Good for heavy topsoil. |
| Bagged raised bed mix | One product | Easy for one or two small beds. Buy one labeled raised bed mix. |
If your topsoil has a lot of clay, University of Minnesota Extension says you can add some sand to loosen it.
What to Avoid
- Potting soil. It dries out too fast in a bed. Keep it for pots and seed trays.
- Mostly compost. Too much compost dries out and can repel water once dry.
- Lots of manure. Manure and composted manure are high in phosphorus. Use them only when a soil test calls for it.
- Peat or coir as the main fill. Both dry out like potting soil. Peat also has environmental concerns.
- Soil from an unknown site. Bought-in soil should not come from ground with plant disease, lead, or pesticides.
Under the Bed
You do not need a barrier between the bed and the ground. University of Minnesota Extension says a barrier can stunt roots. Kill the grass first, loosen the ground with a fork, then set the frame and fill. Add hardware cloth on the bottom only if voles or gophers dig in. On a patio, a water-permeable landscape fabric holds soil in.
Fall Is a Good Time to Fill
Soil and compost are easy to get in fall, and a bed filled now has all winter to settle. Top up the low spots in spring, then plant. Want to use your fallen leaves instead of buying fill? Build a no-dig bed.
Related
Sources: University of Minnesota Extension, Raised bed gardens; Utah State University Extension, Raised Bed Gardening.