Based on the results, this fall I redid my garden beds using:
1. Vertical hugelkultur
2. Large quantities of wood chips dug in the soil.
In small test beds this year these 2 techniques did the best.
Just completed 4 beds, here are pictures of building one.
Dug down average of 2.5 feet. At that depth I hit a layer of pottery-like clay that would be unusable for garden soil.
This bed is 3.5 feet wide and 12' long.
Added wood scraps, from splitting wood, at the bottom.
First layer of vertical stumps, packed closely together.
Added dirt mixed in with wood chips and then put a 2nd layer of vertical stumps.
More dirt and lots of wood chips.
Added a 3rd layer of branches, partially rotted and began building retaining walls from logs and 1/2" rebar.
No pictures, but did add a 4th layer of larger branches placed horizontally on top of here.
Here are 2 completed beds, built with retaining walls.
Also made 2 other beds without retaining walls. Those ones only had 2 layers of logs, one vertical, one horizontal. So they did not raise the soil level as much.
The only cost for these beds was the rebar (~$30). All the logs, stumps, and chips were free. Lot of digging though. Didn't get a chance to go to the gym for the last 6 weeks :)
Roughly the top 6" or more of soil in each bed does not contain logs or branches, just dirt and wood chips. This is to make it easy in future years to dig in more wood chips with a normal shovel if this will be needed. The soil is very thick clay and I believe I'll need to dig in more chips in a couple years.