So Melissa Miles says to fill in the spaces between the logs and top off the bed enough to cover with 1" to 2" topsoil and mulch. Doesn't sound too thick. I'm wondering if your sod would be fine barring any issues from the aeration decreasing.
I'm converting my keyhole-designed garden beds into hugelkultur beds next year. It will follow a swaled contour on which I have fruit trees planted on the down side berm. I'm debating on what type of logs I should get since I currently live in suburbia and don't have the benefit of culling a food forest property.
Fellow Permaculture Enthusiast
Melissa Miles from the Perm Research Design Institute website:
Creating a hugelkultur garden bed is a relatively simple process:
1. Select an area with approximately these dimensions: 6 feet by 3 feet
2. Gather materials for the project: Fallen logs, branches, twigs, fallen leaves (the “under utilized” biomass from the site). Avoid using cedar, walnut or other tree species deemed allelopathic. Nitrogen rich material (manure or kitchen waste work well and will help to maintain a proper carbon to nitrogen ratio in the decomposing mass within the hugelkulter bed).
Top soil (enough to cover the other layers of the bed with a depth of 1 – 2”) and some mulching material (straw works well).
3. Lay the logs (the largest of the biomass debris) down as the first layer of the hugelkulter bed. Next, add a layer of branches, then a layer of small sticks and twigs. Hugelkultur beds work best when they are roughly 3 feet high (though this method is forgiving, and there is no fixed rule as to the size of the bed. That is where the “art” comes in!)
4. Water these layers well
5. Begin filling in spaces between the logs, twigs and branches with leaf litter and manure of kitchen scraps.
6. Finally, top off the bed with 1 – 2” of top soil and a layer of mulch.
The hugelkulter bed will benefit from “curing” a bit, so it is best to prepare the bed several months prior to planting time (prepare the bed in the fall for a spring planting, for example, in temperate northern climates), but hugelkultur beds can be planted immediately. Plant seeds or transplants into the hugelkulter bed as you would any other garden bed. Happy hugelkulturing!