As a result, large, overgrown specimens are often leggy and unattractive. Old, neglected lilacs can be renewed or rejuvenated by pruning.
Home gardeners can choose between two different pruning methods. One way to renew a large, overgrown lilac is to cut the entire plant back to within 6 to 8 inches of the ground in late winter (March or early April). Jul 08, The less drastic approach to getting an overgrown lilac back into shape is to use the third rule. Prune a third of the oldest branches all the way to the ground each year for three consecutive years. Start by taking out the thickest stems first. Lilacs bloom on newer growth, so the blooms will be on the new younger branches growing out from older trunks.
Therefore as the bush gets older and older and puts out more and more new branches, since it blooms better on those newer branches, gradually the blooms are all way up high and unreachable to gather for bouquets. Old lilacs can be cut back to a foot high in late winter, but I don't know about trying that in June, and definitely not if you want flowers next spring.
Lilacs bloom on old wood, not new shoots. I'm sure that your bush will send up lots of new growth now, and I would put off cutting back any branches during the growing season until you see some.
Aug 27, The Lilac borer (or ash borer, a type of clearwing borer moth) tunnels into lilac branches. Signs include sawdust, sap and frass (excrement). Some plants tolerate this damage. Others experience dieback of branches and sometimes death of the entire plant. People are unlikely to notice them. Jun 10, If the trunks are very thick, you may need a saw. Cut each branch back by 1/3 to 1/2. The lilac will grow back, but it'll take a season or two. If you discovered that your plant was grafted, be sure not to cut below the bushfelling.buzz: K.
Trim unhealthy branches after carefully selecting the five strongest branches and loosely stringing them at the base. Using garden shears, cut all other branches about 1 inch from the ground. Be careful not pull or tear away at any of healthy limbs. Remove string from remaining bushes. Shrub lilacs and bush lilacs are short and compact. Tree lilacs can grow up to 25 feet ( m.) high and have a tree-like appearance, but their many stems tend to get them classified as bushes.
They are not technically trees, but they get big enough that you can treat them as if.