I'm wanting to do some high density planting with some new apples trees, pear trees, peach trees. I'm wanting to way overdig the hole when I plant these new trees. for high density planting, the trees are spaced approx. 5-feet apart. So I'll have three trees and each center will be 5-feet apart. I'll mark the area and dig out ALL of the soil in that area. I'll dig to a depth of approx. 4-feet. Then I'll pile on some firewood logs, compost and some grass clippings to add nitrogen. Then I'll just top it all off with the soil I dug out of the hole. Plant my three trees at their 5-foot interval (in a triangle pattern). My thinking is I'm creating a mico-hugelkulture mound. Will this work? because we're going to have two rows. that means one row with FOUR high density tree clusters. And a second row with three high density tree clusters. So SEVEN holes four feet deep. I'm very open for suggestions. I'll have a guy with a backhoe for the dig.
I think the organic matter might sink, thus disrupting the tree roots over time. Also, the area might turn into a sort of pond, and drown the trees. And compost below ground could generate alcohol which could damage roots.
But I am not sure I understand exactly what you are trying to do. So maybe my criticisms are irrelevant.
I have some above-ground hugelkulture mounds. But I've seen where people are digging a trench and putting a lot of the logs underground. Supposedly the logs will act like a sponge and retain moisture and as they break down, they help provide nutrients to the soil. But this is my first year with anything hugelkulture. so I'm trying to experiment with it. I read good things I haven't seen anything specifically talking about small hugelkulture experiments. However, to plant three fruit trees on a 5-foot spread, the hole would have to be 8-feet in diameter x 4-feet deep. I would pile logs up t abut 2-feet. Then I would add about 6" of grass clippings to compensate for the nitrogen problem associated with hugel mounds. Then I'd add 6" of topsoil plant the three trees. And top it all off. on the surface I'll use a couple sections of newspaper and wood chips to sheet mulch to inhibit weeds. But I honestly have no idea if it will work or not. I had never thought about the fermentation of alcohol.
just trying for a little more research before I plant 27 *expensive* trees. That would suck A LOT to do all that work and spend $50/tree, and then watch a catastrophic fail happen in my front yard. so still in research (and ASK people smarter than me) phase.
I planted a jabuticaba tree (look it up - they're awesome) down in South Florida on a pit filled with chunks of a downed tree. I packed it down as hard as I could and watered in dirt, etc., before I planted.
A few months later, the area had sunk in by a few inches and started to eat the young tree. I had to dig it out, add more fill, then re-plant.
I think the idea is sound; however, you may want to wait for settling to occur before planting. Either that or just plant tree seeds and let the young trees adjust as conditions change. They seem to be a lot more resilient.
Logs would not be such a problem as far as alcohol, bad bacteria, etc. But grass clippings certainly would be. They would mat together into an airless mass, rather as if they had been stuffed into a trash bag. And all that stuff would be right under your trees.
Well I tried putting organic matter in those holes for the trees. It looks like the trees sank down some. I ended up losing quite a few trees (mucho sadness). of the 23 trees I put into the ground, only eleven trees survived. Oh well. Fall is here again. I'll be planting some replacements (big sigh).
One thing I tried on a whim, when all of my trees were looking really awful, I went to the local fish market and go ten gallons of fish guts. I made a water-slurry of that fish and poured a significant amount around all of those trees. Some of the trees I thought were DEAD ended up coming back.