I have an old lilac bush that I would like to propagate. Suckers work, but I would like more control over amount, uniformity, and size. I had heard that they root readily from hardwood and semi-ripe cuttings, but after several failed attempts, I came here for some help. So, how are these cuttings taken?
From this site
Propagation by cuttings is one of the most popular ways to propagate lilacs. Cuttings should be taken when new green terminal shoots are produced. They should be four to six inches long, but should not be left out too long, because they will wilt easily and die. The cutting should be dipped in a rooting hormone like IBA (Indolebutyric acid) which aids the plant. The cuttings can be placed in a media with peat, vermiculite and perlite. Each cutting should contain 2-3 nodes, which are the growing points where the leaves are attached. The leaves aid in rooting by producing carbohydrates for the rooting plant. The cuttings should never be allowed to dry out and should be kept moist at all times. The cutting should root within 3-6 weeks. Once roots appear, you can place the plant outside in a desirable location.
What should be noted is that you need strong shoots that have a little bit of woodier stem and you need the strongest rooting hormone you can get. It used to come in three strengths and I recommend the strongest.
Take cuttings in the spring.
Try various rooting mediums but constant moisture, higher humidity levels and bottom heat are required. The quote recommends an artificial soil-less mix but I would also try floral foam, glasses of water or even pure perlite.
The trick with cuttings is lots of humidity to compensate for the lack of roots, lots of light and air movement to prevent mould. For many this means a greenhouse.
Well I must have gotten lucky because I was doing a clean up pruning of my dwarf lilac in early spring here in zone 4b. I took a cutting that was crossing through the plant and for fun just stuck it deep in the soil next to my other lilac. What do you know? It now has leaves and flower buds and looks pretty happy. No rooting hormone either.
I cut back my lilac bushes to make them into trees. Had close to 100 cuttings. Just for fun we dug 30 holes in a row and put the drip system on them and put 30 of the cutting straight in the dirt. No fertilizer, or growth hormone. Just water. And we are in Northern Nevada in harsh desert bad soil conditions. 23 of the clippings never wilted. They also rooted. How do I know? That was 2 years ago. The clippings are now 6' tall.