Not true in my case. We got tree surgeons in to do the job. They told us
we could chop off one-third of the height at any one time; then give the
trees a year or so to recover, and then take off another third of the
height. We've done this successfully (touch wood) on our hedge. Now we
trim the hedge back twice per year (spring and autumn).




"Dave Painter" wrote in message
...
Leylandii, do not grow from old wood so lopping the top off will cause the
trees to die back.
They need to be trained from an early age, regularly and frequently.

If they are 20 foot now you should be able to take off about two foot,
then
in three or four months
take another foot off.
Then you will be looking at taking new growth off every three months.
Hopefully your trees will 'thicken up' and become more of a hedge/bush
rather than individual trees.

My fathers trees did not, they gradually died back from the base until all
that was left were the trunks
about 12 foot high. These have been pulled out and replaced with a garden
fence.

Our neighbour had hers removed when it hit 80 foot after about fifteen
years
growth.

YMMV

Dave