Jaques d'Alltrades wrote:

However, what's done is done. Compost or well-rotted manure can be
spread as a mulch and the worms will soon take it down into the topsoil.


That's the intention.

Excellent. If you can bear the sight of it, you can pile cardboard,
grass mowings, manure, kitchen scraps (but not meat, it attracts the
rats), straw, paper etc to knee-height, water it well (with added urine)
then cover it with black plastic, peg the plastic down and leave it
until spring.

In the meantime, your friends the worms will get to work, and you'll
find a fine tilth of well-structured soil when you uncover it.

It'll take a long time in my experience to rot Leylandii, it's more
resitant than most to rotting (which is an advantage if you use the
timber outside). We have cut down quite a number of large (up to 18"
diameter and 50ft high) Leylandii and also had some Aspen trees felled
for us. The aspens rot away in a year or so, none of the Leylandii
show any sign of rotting yet.

--
Chris Green