The message
from Chris Hogg contains these words:

I've just taken out a leylandii hedge and want to improve the soil
before planting something else next spring. I have access to fresh
horse manure. If I dig it in this autumn, will it have
rotted/composted or whatever, sufficiently so as not to damage the
roots of the new plants when I plant them next year?

Should do - as long as it doesn't freeze from the time you put it in to
the ime you plant the new hedge.

I'd suggest putting bonemeal and bones in the bottom of the
trench/holes. Releases calcium and phosphates very slowly.

--
Rusty Hinge
horrid·squeak&zetnet·co·uk
http://www.users.zetnet.co.uk/hi-fi/tqt.htm