My mother was a lifelong rhododendron and azalea enthusiast, around age 60 she decided to establish a new species bed. The bed was roughly triangular about 60' on the short sides. With a small stream running along one side. She determined that the native soil was inadequate for the task and needed to have the rocks screened out and amendments added - the top 2' (yep 24" here). The soil was clay loam so it was determined that it needed to be amended with sharp sand and decayed wood. The sand was delivered 10 yards at a time as she needed it, the decayed wood was mined out of every rotting stump within several hundred feet of the work site.
My folks lived on about eight forested acres on a mountainside, the stumps were left from the place being logged in the 1920s, most were Doug fir and cedar, 6-12' in diameter and up to 10' high.
She worked on this project and completed in about 3-4 years, when she was done the stumps were piles of the un-rotted bits with several 10-12" hemlock standing on 8-10' tall buttress roots above the remains. The species bed was done, she planted it with a wide variety of rhododendrons from dwarfs to tree types.
I do not know just how many yards of soil she sifted or how much sand and rotten wood was incorporated into it. Bottom line is this was done by a survivor of breast cancer who had two radical mastectomy operations that had taken all of her chest muscles as well.
The rhody bed exists to this day, the last time I saw it about four years ago the tree types were thirty feet or more high. I hope the folks that bought the place can appreciate it! I also hope that they like rhododendrons and azaleas because that project was not her first or last just the biggest!