Mike

I have read reports on here that if you trim a Leylandii back to the
trunk/bare branch it won't grow green stuff again. This was just after I
had taken one right back to said trunk and bare branches :-((

2 months later growing the green stuff and now a lovely screen again
:-))

Mike

I agree with Mike. I've also seen Leylandii bush up to a thick hedge
from bare trunks after the green top was cut off.