Question
I live in Monroe Washington and have 5 lilics bushes that have been in the ground 6 years.  Please give information on cutting them back.  I want them to be shorter so do I cut them back down to about 6 inches off the ground so they can grow back up to 3-4 feet?  

Answer
Lynette,
It's tough to keep a regular lilac at 3 - 4 feet.  Even the dwarf "Miss Kim" lilac grows to 5 feet tall and wide.  If you cut them to the ground, they will shoot up FASTER then before, mostly tall, straight growth.  This is because when you do a renewal pruning and cut a plant to the ground, the plant wants to replace what it's lost as soon as possible - the leaves feed the root system, so the plant works quickly to replace them in order to sustain life.  

Yes, you can do a such a renewal pruning on lilacs, but I think you'll be unhappy with the results - the plant will put out straight, tall shoots and these won't start blooming for about 4 or 5 years, and once they start to bloom they will be too tall again.  The other strategy would be to prune them down my half, but again, the plants will work to replace what they've lost and it will take a few years to start blooming again.  

In short, lilacs are not a good plant for trying to control growth and size.  If it's not possible for them to grow to their full height (the size of small trees) I'd transplant them to a location where they can grow naturally.  

If you want to try the renewal pruning first, do it in the spring (April or May - if you want you can wait until just after bloom) and once they are cut down water the plants well once a week if it doesn't rain.  Don't fertilize - if you do it will just make the plants too tall too quickly.

I hope this helps!
C.L.