"Janet Tweedy" wrote
Lilac that's never been pruned? How do you even go about working out
which third of the stems need doing. Is it best to take out weedy
growth first then 1/3 rest of stems? Looked it up in books but though
they say in a cavalier manner, that you just pruned after flowering
and take out a third it doesn't help much if you can't see the wood
for the trees! Can't find anything much on the smaller rarer lilac
either.

Any advice would be appreciated.

I don't know how you'd tackle a very large common lilac, but last year
we cleared an area where I'd got a rather overgrown and out of shape
small flowered one (I believe it's Syringa meyeri) which must be at
least 20 years old. I cut it right down to a stump about 9" from the
ground in a kill-or-cure fashion. This year it has sprouted lots of nice
new shoots all round and is making a neat little shrub again. So as far
as this type of lilac is concerned it seems to be tough as old boots.
--
Sue