Step 4: This step is to help build the soil up, while also leveling out the surface area, and to provide nutrients to the garden bed, as the organic matter decays and turns into soil.
We heavily covered our cardboard with lots of leaves (the leaves were at varying stages of decomposition,) grass clippings, and wood ash. For the wood ash I took burnt charred logs from my fire pit and crumbled them up in my hands almost into a powder. The wood ash will provide nutrients while also acting as natural insecticide and pesticide.
It’s okay to put larger chunks of wood ash in the pile also, as they will decay and will hold nutrients - slowly releasing nutrients over time during the decay process.