Question: Lilacs: the ones I have are old with 3-4 inch trunks as well as many younger ones and countless suckers. I have pruned out over years and tried to maintain 3 to 5 of the old trucks (per plant) in the tree form. I cannot keep up with the new sprouts and the suckers are always spreading outward from the plant. I have cut out suckers with root back to plant, placed weed fabric over surrounding ground, etc. but they just keep coming back. How in the world do you “train to a tree form” or at least eliminate the sucker/sprouts?
Last year I purchased “Sucker Stopper” for D&B and it worked well on some but is awful expensive and did not go very far.
Answer: Thank you for your question!
Keeping suckers from forming on a lilac is darn near impossible as that is just their growth habit. Training to a tree form takes diligence and much pruning. Just continue to cut off or treat the suckers and keep the main trunk pruned down to a reasonable height. To rejuvenate an old lilac, plan on pruning out 1/3 of the stems this year, 1/3 the second year and the last 1/3 on the 3rd year. This will encourage new suckers to fill in and replace the ones that have been cut out. That won’t help with getting a ‘tree’ form but it will work with the suckers that want to continue to grow.
There is a tree that is called a Japanese Tree Lilac (Syringa reticulate) that is a tree. It has plumes of white lilac type flowers that bloom in late spring and is a smaller tree. It won’t get above about 25 or 30 feet tall.
I hope you find this helpful. Happy Gardening!