If the lower portions of your mature lilacs, which are most likely shaded, are losing their leaves the plant will usually become leggy and unattractive. This means that you have become the owner of an overgrown and large lilac plant that needs your help. This can be very unattractive with a large plant, and the common purple lilac can reach a height of 15 to 20 feet when mature, so they do become quite large. These older or neglected lilac plants can be rejuvenated by correctly pruning them. There are two methods available for home gardeners to choose from with lilacs in this situation.
The first method is to cut the whole plant back to within 6 to 8 inches of the ground during late winter, which for most of us would be March to early April. Severely pruning the plant in this manner will induce a large number of shoots to appear during the next growing season. Let the plant go during this growing season, but in late winter cut back all of the smallest, weakest shoots to ground level and keep several of the strongest and healthiest shoots. In this manner you will begin to form the framework for a better and healthier plant. On the shoots that you have chosen to keep, to encourage branching, cut them back to just above a bud.
The second method will be performed over a three year period. Begin during the 1st year in late winter. Start by removing about 1/3rd of the old large stems; be sure to cut them back to ground level. During the 2nd year, once again in late winter, cut out about half of the remaining old stems. Once gain make sure to cut them back to ground level. Also take this opportunity to thin out some of the new growth that has occurred during this time, making sure to leave several of the healthiest, well spaced new shoots and stems. During late winter of the 3rd year, remove all of the old stems that are remaining and once again thin out the new growth and shoots, keeping the strongest and healthiest. Lilacs typically bloom at 3 years of age or older, so this method will allow you to enjoy some blooms each spring till you have rejuvenated the entire plant.
When properly pruned, an older neglected lilac can be turned into a plant that will be a wonderful addition to anyone’s lawn or landscape and can be accomplished in only a few years. After reaching this point, pruning should become a part of the regular maintenance for your lilacs. Removing the oldest branches every 3 to 5 years will help keep the plant healthy and vigorous for years.
