Why would Back To Eden work if you don't improve the soil first?

I have some seriously dense clay soil. It's so dense that some trees don't grow at all after several seasons because the roots never manage to grow out of the brick soil they're in. I mulched heavily but the soil underneath was still solid. I'm also surprised by people who layer cardboard and just dump mulch on top, then plant trees by cutting a hole through and planting in the same original soil.

Anyway I've dug out my soil, filled it with heaps of woodchip mulch, then thrown some of the soil back on top. It rained and after I dug into it just a few days later I can't even really see the mulch underneath- the clay soil has somehow saturated it all. It feels really nice to step on though, very springy and bouncy.

Tim,

Sounds like you have already done your soil some good.  Regarding your specific question, unless it is dead soil—also known as dirt—the soil will contain microbes that will try to break down woody material.  As the chips sir and rot, the pile and soil beneath will start to merge.  Fungi will reach into both chips and clay.  Earthworms will tunnel into both wood chip and clay, mixing the two substances.  Basically just piling on the mulch and doing nothing else will by itself start to heal up your soil.

Eric

I hand tilled the clay with a pickaxe and shovel, added a lot of chips that had composted somewhat for about a year, and then took the broadfork to it.  It really does break down; can just take time.

It takes a lot of time for clay soil to start breaking down.  

I have a couple of areas with clay soil that were chipped for a couple of years but it wasn't as effective as my loamier areas.  I started using the clay areas to pile any kind of biomass I could find.  Also planted some basket willow.  The soil  is getting better.

If your entire garden area is like this you might consider doing some raised beds or hugels to get started with.  Just keep piling on leaf litter, trimmings and etc.

Tim Kivi wrote:some trees don't grow at all after several seasons because the roots never manage to grow out of the brick soil they're in..

This mainly happens because trees are planted in a hole back-filled with improved soil.  It might work better to fill the hole with the native clay so the tree won't feel inclined to keep it's roots in the hole.  Trees are quite capable of rooting through clay.

Try planting loads of daikon radish and leave them to rot in place.  Your yard will smell like rotting cabbage for a while but it really does help.

Healthy soil is a diverse ecosystem. The biota need habitat - food, water, shelter, space - and wood chips provide all of those things directly or indirectly (ie holding water). As mentioned above, the life does the improving of the soil, while the woodchips give it all a safer and richer place to live while they work.

Tim Kivi wrote:some trees don't grow at all after several seasons because the roots never manage to grow out of the brick soil they're in..

If what you're saying is, you dig a hole in the clay, fill it with good soil, and plant a tree, the tree roots might just try to circle within the hole where the good soil is, and not grow properly.
(This is what @TylerLudens is mentioning two posts above)

There are three things you can do to help:
A) Improve the soil *beyond* just the hole you are digging - pile woodchips on, plant diakons, etc... so when the tree roots really start going in that direction after the first two or so years, the soil will have somewhat improved.
B) Dig a *square* hole (roots reaching the corners will be steered towards the clay, rathering than hitting the clay wall and then just going in circles).
C) Mix your good soil with half the native "bad" soil, so the tree is acclimated to it. Chop up any native clods you are putting in it though.

Basically, you don't want an extreme wall-like difference between your tree's starting soil and the soil it'll eventually need to grow into.

As an additional note, Back-to-Eden reduces water requirements, but doesn't eliminate them during droughts or when first planting the tree. Especially during the first year of the tree's growth, make sure you water it. And even when it's a year or two old, give it some good drinks during intense summers or long periods without rain.

Good points Jamin. On your note about “back to eden” being more than just woodchips, an oft forgotten component of his system is that the woodchips were used as chicken bedding first. This obviously means they had nutrients added in manure, and the chicken scratching and biota in the bedding broke it down and turned it.