Nick writes


Light and better conditions are now available to the lilacs.
If I take some of the weight out of the crowns are they ever likely to do
well or succeed?
I really don't want to cut them down. My wife and I enjoy both the plants
and the blooms but there is also some sentimentality on my part.

If they were mine, I would cut back the almost horizontal 'trunk' by
about half, leaving any branches that are growing near the 'base'. That
would encourage more new shoots from the 'base', which, now the
leylandii are gone, would tend to grow vertically. They would start
flowering in about 3 or 4 years. Once the new growth is really
established (2-3 years time), you can cut the horizontal stuff back more
and more.

Even though lilac is tough, I don't like cutting back anything too
severely because there's always a slight chance it won't recover. So I'd
look to be pruning and re-shaping over about 3 years (with other shrubs,
an accepted technique is to cut about a third of the branches right down
to the base each year).

If you do do the job gently over a few years, you can always keep a
straggly branch or two to make sure you have some flowers each year.

Don't overdo things, and let the plants teach you how to go about it.

This heavy pruning can be done over the winter (not when frosty) while
the tree is dormant.

After-flowering pruning in the spring is light tidying up of a tree that
is already in good shape. Doing it in spring allows the whole summer
for regrowth and formation of flower buds - you won't get any flowers
the following year on branches that have only had the
autumn/winter/spring to grow in.
--
Kay