How to Layer
All of your layering materials need to be organic and toxin/petroleum free. Over time, the base layers will decompose, but remember how deep your layers are when digging and turning soil so as not to disrupt your course, raw material.
1. Wood: Lay a thin layer of small twigs, branches, or bark at the bottom of your raised bed. You can also add other materials like newspaper and manure at this first step.
2. Less expensive soil: Add in a less expensive soil or loam, old potting soil, or native soil mixed with inexpensive soil. Don’t add any soil that has weeds in it, potting soil that is moldy or has a pest infestation, or the like. In this layer, you can also add in some leaf mold, compost from your pile, and grass clippings.
3. High-quality soil: Most raised bed plants need 6-12” of good quality soil, so I aim for that depth when I add the “good stuff.” Fill your bed to within an inch under the top edge of the bed — I actually fill mine right to the top, as soil has a way of settling down after watering in.
Note: If you have an existing bed with old soil in it, you can “top” it off with higher quality organic raised bed soil. This is particularly true if your old soil has settled a number of inches down and you not only need better quality but more depth.