You ay a tall screen, What is your idea of tall?
Leylandii can reach a height of over 100ft.Of the 6 seedlings produced in
Leighton Hall, Powys, Wales in 1870 one was measured in 1971 and was just
over 100 ft and growing well
They can.......if happy....put on 3ft to 4ft a year, and I have 3 trees, One
green and the other 3 Variegated which at the age of around 13 years are
well just over 49 ft.
Here in the UK there is a very strong movement to ban the planting of
Laylandii as they get out of hand so fast. They are often planted at 3ft
spacing with the idea of making a 6 to 8ft hedge, then they don't get
trimmed for a year or so and neighbours complain that they no longer have
light.
They should be clipped from an early age to thicken them and to hold the
growth rate down a bit, remember they will grow sideways as well as up, and
Nothing grows under them. One of the slowest growing of the family is
Leylandii Castlewellan Gold.
There are now around 14 different clones of Leylandii being grown in the UK.
Just be very careful if you are thinking about planting them.
By the way if you cut back into the old growth they don't regrow and you are
left with a horrible looking mess.

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