To fill a raised garden bed effectively, follow these expert guidelines:
Basic Soil Mix for Raised Beds
- Use a mix of three parts organic matter (such as garden compost, leaf mold, or well-rotted manure), two parts sharp sand, and seven parts topsoil. This blend provides good fertility and drainage for most plants
Layering and Filling Techniques
- For deep raised beds, you don't need to fill the entire depth with expensive topsoil. Instead, use a layered approach starting with bulky organic materials at the bottom, then topping with quality soil.
- Begin by laying down a wire mesh or hardware cloth to prevent rodents, then add a layer of cardboard or shredded paper which will decompose over time
- Add large organic materials such as logs, branches, wood chips, straw, or leaves as the bottom layers. These materials decompose slowly, enrich the soil, improve aeration, and retain moisture
- On top of these layers, add a mixture of native soil, compost, or potting mix to fill the top 12 to 18 inches, which is where most plant roots will grow
Benefits of Using Organic Fillers
- Logs and branches add nutrients as they break down but may cause the soil level to sink over time, requiring annual top-ups of soil or compost
- Straw and leaf mold decompose faster, improving soil structure and microbial activity
- Compost should be mixed into the topsoil layer to provide nutrients and support beneficial soil organisms
Additional Tips
- For beds with compacted or clay soil beneath, loosen the subsoil before filling and consider mixing compost with purchased topsoil in a 1:1 or 1:2 ratio for the top layer
- Use weed barrier cloth or burlap at the bottom of the bed to prevent weeds and soil erosion
- Water the soil after filling to help it settle and fill any air pockets
This method balances cost, soil quality, and plant health by combining inexpensive organic materials at the bottom with nutrient-rich soil on top, ensuring a productive raised garden bed.
