enigma expounded:

lots of suckers from the roots.

Good. I've seen old lilacs that are reduced to only one trunk, they
don't seem to survive being cut back severely (the farm I work on has
lilacs that hadn't been trimmed for over fifty years, two of them died
when the Squire cut them back against my wishes. He's the boss, but
sometimes I really wonder why he asks me).

Cut back each plant after they bloom - and take out the largest trunks
completely. They say to get an overgrown shrum under control to cut
back by one third over a three year period.

do lilacs respond to layering as a propagation method?

Yea, but why not just dig one of the suckers with roots and use that
to increase?
--
Ann, gardening in Zone 6a
South of Boston, Massachusetts
e-mail address is not checked
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