Penney. 

It's understandable that your lilac bush suffered during the drought. Lilacs are relatively hardy, but extreme conditions can definitely take a toll. Pruning your lilac bush can help it recover and thrive again.

The ideal time to prune lilacs is immediately after they finish blooming in late spring or early summer. This is important because lilacs set their flower buds for the following year on "old wood" (growth from the previous season). Pruning too late in the season will remove those buds, resulting in fewer flowers next year. However, when dealing with a plant that has been stressed, you can also do some pruning during the dormant season. Late winter or very early spring, before new growth begins, is Ok for removing dead or damaged wood.

Tips for pruning lilacs. Remove the dead wood first. Prune out any dead, diseased, or damaged wood at ground level. This helps improve air circulation and light penetration. Air circulation and light penetration will help keep the plant healthy. Prune about one-third of the oldest stems to the ground. This method, known as rejuvenation pruning, stimulates new growth. And If you want to control the size of your lilac bush, trim back the younger stems by about one-third of their length. Always cut just above a pair of healthy buds to encourage proper growth.

Recommendations for a lilac recovering from a drought. Avoid heavy pruning, especially in the first year after a drought. The plant needs time to recover. Watering, ensure the lilac receives adequate water, especially during dry periods. Deep, infrequent watering is better than shallow, frequent watering. Mulching, apply a layer of mulch (2-3 inches) around the base of the plant to help retain moisture and regulate soil temperature.

Summerizing

• Prioritize removing dead and diseased wood.
• Thin out older stems gradually.
• Water and mulch to support recovery.

Here are links to university factsheets on pruning and caring for lilacs. Thank you for using Ask Extension.

Minnesota

Iowa State