How can I prune a VERY TREE-trunk like lilac?

Question

The plant is basically this one thick stem (never maintained) with a few branches off of it. Even the branches are like tree-thickness.

It is basically one tree stalk with branches off of it (never maintained).
I need to know what to cut; should I leave any of it; and HOW/with what to cut such a thick stalk?

Answer 1

You could try to force it to produce buds lower down on the stem by cutting off the top by one-third. Then next year cut it down again to 1/2 the origianl height. Is there enough light to support lower branches? I heard this works for shrubs that can produce new bud, but is does not work for many evergreen trees like spruce.

Answer 2

An overgrown lilac will never bloom well. Most of the wood on it is too old for flowering and for all you know is the privet base that the original lilac was grafted onto. You would be better off cutting it down and starting with new 2 year-old ones.