I would appreciate the advice of the learned folk here please.
We have 2 lilac trees (Syringa, I think) in very close proximity. One bears
white blooms, the other purple.
You may have guessed that I am a beginner.
These were planted by my mother 40-50 years ago. A few years later my father
planted some leylandii immediately to the south of the lilacs to provide a
screen.
Neither the lilacs nor the leylandii have seen any attention in many a year.
The leylandii grew to 12m+, put the lilacs in permanent shade and demolished
the garden wall.
The lilacs slowly reached out for light (I am presuming) until the main
stems/trunks were about 30 degrees above horizontal and were only supported
by the remains of the garden wall. If upright they would be 5-6 metres
For reasons I won't go into here I have not been able to give this much
attention since my father passed away 5 years ago.
For the last 4 years I have jacked up, and propped, the trunks of the lilacs
a few inches every winter. They are now at about 40 degrees.
Severe winds and prevailing conditions have caused the leylandii to
'disappear' over the last few weeks and the lilacs will now be able to have
the benefit of full sunlight.
It is lovely to see these once again. Also I can rebuild the wall and
reinstall a gate.
I have googled for advice which ranges from prune in autumn to prune in
spring immediately after flowering to cut it down at ground level.

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.

Thank you,
Nick.