We built our raised garden beds 2.5' tall for ease of use, but when it came time to fill them I looked for a low cost solution. We knew we needed to bring in good soil for the garden since our native dirt is mostly clay, but the cost of that much topsoil was shocking!
Then I stumbled upon Hugelkulture, a gardening technique in which you layer compostable material like logs, branches, leaves, hay, and compost.
The decaying wood and composting material provides long term nutrients and generates heat. The logs and branches store water and slowly release it back into the soil. A win for your plants and wallet!
See the quick video tutorial and pdf document for more information!