Question
Hi Tom, I bought a 5Ft Lilac bush last year and it did great the 1st year. A few weeks ago I trimmed it and now has only a few flower on it. I just learned that the flower will come on the old branches and not on all of them so I would like to prepare myself for next year and to know when to prune and how much... Oh and there are liitle 'sprouts' coming up around the base now too.
Can you help me?
Thanks, Mirella

Answer
Hi Mirella,
Thanx for your question.  The best time to prune lilacs is after they have finished blooming.  Don't prune too severely.  Just deadhead the flowers. I would just remove dead growth and growth that is unkempt.  The little sprouts coming up at the base are called suckers.  I would keep these down to a minimum and dig them up.  You can give them away or compost them but if allowed to grow, they will take energy from the main plant. You can allow some to grow to replace dead growth.

Lilacs do not require annual pruning, however cutting off blooms from main
stems within a week after blooms have faded will help the plant concentrate on preparing more flower buds and not seeds. If your lilacs become too tall, and the number of blooms declines, you can rejuvenate the plant by cutting 1/3 of all main stems that have a diameter of at least 1-1/2 inches.  

Cut these main stems down to 12 to 15 inches from the soil. This will
stimulate the growth of new shoots. Pruning in this way over a three-year period will refresh the plant while it still continues to flower.

I hope this helps.
tom