Our landscaper planted several Korean lilacs around our house and I just love them, but I'm not much as a gardener. I've been researching, trying to find when is the best time to trim them because they're getting too big (over 5' tall, covering the first floor windows of the house, which we don't want), and I found they're supposed to bloom twice a year! I suppose they haven't because we've been trimming them every summer or fall. Is there a "best" time to trim them, and is there anything I should to do help them have more blooms? They were trimmed late last year and didn't bloom much this spring. I haven't fertilized them - they've grown like crazy on their own. They've been in the ground probably about 8 or 9 years. Thanks for the help. Lynda
Each time they start to block the windows, start them over by cutting all stems to 18" in winter. You will get no bloom the spring after that but later this treatment will give you a period of years where they look natural and are able to bloom normally. If they get in front of the windows again too fast for this to appear to be working well then dig them up and put them elsewhere - in another part of the yard, on other property, or on the yard waste pile in the transfer station.
You could also prune a bit less vigourously, to keep them looking lovely in the meantime. It really depends on how quickly they're growing, and what you're willing to do when it comes to maintenance. Remember to make clean cuts so as not to let in pests and pathogens. Make your cuts just above an axis where the tree/shrub has buds or eyes below. There are lots of great photos of this on-line, just look up "pruning lilacs" and you should get some great hits. Lilacs can take a lot of abuse, but I've had best results from generally taking off no more than 1/3 of the plant at any given time. You can do more, but it's up to you! Ron B gives you the easiest way to take care of them if you really don't want to be out there every year giving them the snip-snip. Always take out dead and diseased wood, or any broken or cracked branches.
Thanks! They're very healthy, with no broken or diseased branches. They just grow like weeds and need to be cut back so they don't block the windows!
