When is the best time to trim trees and bushes?

Question

Mature Aspen has drought damage, brown, unproductive branches. Lilac bushes had very little blossoms, growing out, not up.

Answer 1

late fall......................lilacs need old cow or horse manure and a ring of lime 18 inches from center.

Answer 2

You can take down the dead branches of the aspen know or tie the dead branches with landscaping tape and do the job once the leaves drop.  the tape will direct you to the branches that need pruning.

the best time to prune the lilacs is as soon as they stop blooming.  Take off the branches that have no leaves.  Cut off the dead blooms.  Prune back rangy branches  up to one third of their length, but always leave some leaves on the branch.

If you are at least 3 months from your first frost day go ahead and fertilize the plant with an acid based food such as those for rhodys and azaelas.  This will generate some plant growth well in advance of frost.  Fertilizing later will only produce growth that is frost tender and will die.