"..... can strimm ok but risk damaging the bark and lower branches on the
beech plants (already tried). ....."

I have used 2 litre pop bottles , cut off top and bottom, then cut up the
length at a slant.
The remains of the bottle coils down like the Tree guards you can get, Gives
young stems protection from strimmer, and will expand as the tree/bush
grows.

--
David Hill
Abacus nurseries
www.abacus-nurseries.co.uk