My garden is flanked by a number of evergreens, including Leylandii and
Cypress, which were planted back in the 60s.

Last year one of our Leylandii completely died. We had it cut out, by
the guy who trims them each year.

I'm now really concerned as the same seems to be happening to my 20ft
Cypress and, to a lesser extent, to my 35ft Cypress planted a few feet
from the stump of the Leylandii.

Is there anything I can do to save them, they're considerably more
attractive than the neighbours!!

First thing to do is figure out why they're looking bad... insects,
disease, root compaction, climate, soil moisture...

The second thing to know is that by the time most folks notice a tree
is looking bad, it's been in trouble for at least a year or two. Sometimes,
particularly with insect infestations or drought, they can be saved
with prompt action. Sometimes it's just not possible.

As an example the city I grew up in decided to widen a street,
and "saved" a number of nice oaks by building smallish retaining walls
around the rootball about halfway out from the crown on the street side
and in the process, changing the soil level around the trees,
and then chopped the roots that were where they would protrude into a
road bed. Oaks are pretty unhappy about having their roots damaged, or
even disturbed. Took about 10 years for the trees to die, and the
city spent a lot of money trying to save them -- they really would have
been better off simply removing the trees to begin with and planting
something new. Or deciding they really didn't need a 6 lane city
street. But those trees were basically goners as soon as the first
bulldozer went by.

Kay