Hi,
I'm planning to use a post-hole-digger to bury trimmings from my trees. Those hole will be some on site compost piles to feed the worms and to make bigger stems disappear faster from sight.
Depending on your land, making such holes is a good or a bad idea.
It depends on the water flow and the water table.
If you make such a hole, and your land is hard clay, you may have all water come/flow to the hole ( water flows to the lower point it finds) .
Imagine if you have a high water table ... Water will raise there first.
So I would dig more holes (twice) than the number of trees that I would plant. So that water could escape elsewhere than just at the feet of the trees.
Well, now, I just need to buy a post-hole-digger - I'll go for the manual operated one - although then I need the strength to get it to drill in the dirt... But that's another problem.
For the trashcans, I dug holes of 2'*2'*2' - 60cm*60cm*60cm . At surface level, it was not a problem, but deeper I had to use a hammer, a burin and a crowbar ... That was some nice meal to deal with ...
Believe me or not, but while digging one hole, it was getting late, so I threw a bucket of water in the hole to soften the dirt for the next day ... Well, the next day, I had to use a bucket to empty the hole ... the water was still there ... The clay jar effect, they call it .