Can we trim a lilac back in the fall

Question

We have a lot of dead branches and too much height, just want to shap it for next spring.

Answer 1

You can prune it back without worry of harming the plant, but you will be pruning back the buds for next springs blooms.  They should be pruned back right after the flowers fade. You can prune out the dead branches and thin the plant a bit, and still have a nice display of blooms next season, but I would not do any drastic pruning, unless you do not care about the blooms.

Answer 2

Listen to the plant doctor.  Only trim out dead branches now.  Reduce height after the blooms fade in the spring.

Answer 3

ditto to the two above, also, pruning may encourage tender new growth which would only be damaged by sudden cold.  late summer or wait 'till spring