I have a lilac bush that is about 8 ft from a rental house that I have. it was planted by a renter years ago. now it is getting tall, about 15 ft and is starting to spread out. the limbs are getting so tall and thick that if you cut one off it makes a big hole in the bush. I was wondering the best thing to do with this. cut it down to about 3 or 4 ft and let it start over, get rid of it altogether, ? what would you do?

 

If you cut it down, it'll come back fuller and bushier. They're pretty hardy I think, so no matter how it's cut down, it comes back.
I love them and wouldn't get rid of it.

 

I agree, it's pretty hard to go wrong by severely trimming them. You have a base that is all leafy. Then you have a void in the middle. That void should be your target height. Leave all that leafy base and selectively cut down any large branches that are taller than that. Identify the branch, follow it down to the ground. Then try to cut those branches off as low as you reasonably can without cutting off any of the low canopy branches.

Once the tall stuff is gone you can selectively shape what is left.

I wouldn't chop it all down right now, that would starve the bush of nutrients. It looks like it's just been neglected for a few years.

 

It depends on the look you want and have fast you want to move. At my house, when I want to change the look, I'll trim about 1/3 of the plant to what I want. This can leave big holes but leaves much of the plant in it's original form so it's look isn't so shocking. Also, taking only a portion of the plant reduces shock so it quickly recovers.

With my rental houses I whack them off to the final size I want when pruning in fall, winter and spring. It looks rough for the first month but the plant soon recovers. I would be hesitant to cut back a lilac hard during the hottest summer months unless you really don't care if it lives or dies.

 

All good advice. Each year, going forward, cut a few of the oldest shoots to the ground and that will promote new shoots.

 

You can just cut the lilac bush off at chest height, ~5-feet, with a bow saw and it will grow back fine.

Lilac wood is very soft and tears, so you make two cuts, the first 1/'3 of the way through, then the second all the way through. If you have a consistently damp patch / border area on the property, you can simply jam pencil to broomstick sized trimmings into the soil and about 1/3 of them will root and grow.