Marcia in Cedar Falls wants to take a slip, or cutting, of her dwarf Korean lilac bush. I haven’t found anything specific to dwarf lilacs, so I will assume… unless told otherwise… that dwarf lilacs will act the same as non-dwarf lilacs.
There are different ways to get new plants started from old ones. The main two to try are taking a cutting or digging up a sucker plant right by the parent bush. There is also the layering method.
Although I have found different reports of people doing short pieces, it seems that 6″ lengths are the best to cut from the parent plant. Cut the branch you want at an angle with a sharp knife or clippers. If you are taking this a distance from the parent, keep the cutting moist and cool. Pull the bottom few leaves off the end and dip it into rooting hormone. You can find this at almost any place that has a nursery. Stick it in a pot of dirt and place in a warm spot and make sure it gets plenty of water. The pot will be its home for the first year and then you can transplant it to its new home the second year. It won’t have any flowers until the third year, but it will be worth it. Most of what I read said to take more cuttings than you think you’ll need. It sounds like some won’t make it and if they do, you can always give it to a friend!
Many older plants will have new plants growing near the base. These are suckers or runners. I just did this method a couple of weeks ago with some lilacs for my mom and dad. Pick out a nice tall one, or at least make sure it looks healthy. Dig around it and when you find the main root connecting it to the mother plant, chop through it. Make sure you have as much root as you can get with the baby. You can put this in a pot or just in the ground. Make sure it gets plenty of water and sunlight. Mom said the five we dug up are doing great. At least they were before the big heat and humidity of the last couple few days.
I have heard of this method, but have never tried it. In this method you dig a small trench near the branch you will be using. Leave it attached to the mother plant. Drag the branch down, lay it in the trench with the top part of the branch bent upward out of the trench. Cover the trench, and flat branch, with dirt and pin or prop the bent part to stay up. A couple things I have read on this mention that you should make a little cut on the branch where it is bending up, but other articles didn’t say anything at all about it. And the ones that did, didn’t make it clear which side of the branch to cut. Either way, you need to leave it in the trench for a year to allow for root development and then you can uncover it, cut through the branch in the ground and transplant it to your desired location.
There are a couple of other ways, including seed propagation and they are listed in a handout given to North Dakota State University horticulture or biology majors (it isn’t clear) and is a pretty nice source of information.
All in all, it sounds fairly simple to get lilacs to propagate, but it appears that some of the methods take some time to get results. Whichever way you decide, good luck!