Carolyn Plank, Master Gardener
It’s getting exciting out there! Spring has sprung, the snow has melted, and the rain is bringing us much needed moisture to help our lawns green up and our plants to bloom. One of the most anticipated early blooming shrubs are the fragrant lilacs which come in colors from white to pink to lavender. This article will tell you what you need to know about planting, pruning and some common lilac diseases.
There are several different varieties of lilacs which bloom at various times from April to mid-May, mid to late May, and May to September. They typically bloom for 10-14 days depending on the weather. Lilacs make great hedges, foundation plants and large borders. Once established they can live a very long time. Our lilac bushes lived for over 50+ years until we made the tough decision to remove them.
Lilacs thrive in full sun and well drained soil high in organic matter. Too much shade reduces flowering and can increase powdery mildew. Proper spacing increases air circulation and helps prevent diseases. Two to three years after the plant is established, start fertilizing lilacs every few years with an all-purpose shrub fertilizer. New plantings grow fast when young but may take a few years to bloom. In order to ensure repeating blooms in the following year, prune lilacs immediately after blooming.
This link will take you to a video from the University of Minnesota - Extension Morris on planting lilacs.
Lilacs are subject to several different diseases:
· Fungal disease causes yellowing/browning of the leaves that will die back.
· Lilac borers will cause sawdust, sap and frass (powdery refuse). For more information on lilac borers go to https://content.ces.nssu.edu (North Carolina Extension).
· Verticillium Wilt is caused by two fungi and has no cure for this disease.
· Lilac Pseudocercospora (leaf spot).
· Herbicide damage causes cupping/browning on one side of the plant and not the other.
Use proper plant care such as watering, mulching and fertilizing to help prevent disease. If you find lilac disease you can try various methods to help the shrub. You can try pruning the diseased areas out of the shrub. Remove the leaves that have fallen so they don’t keep reinfecting the shrub. Watch the plant the following year for permanent damage. If you are unsure what disease is plaguing your lilac shrub, you can send a sample to the U of M Plant Disease Clinic to be properly diagnosed. Another option, if the shrub disease is out of control, is to cut it down to the stump. Most likely, it will shoot regrowth. We did this to our backyard lilacs and the bushes came back beautifully.
One last option, which we did with the assistance of a certified arborist, is to remove the diseased plants. We tried to prune out the dead and diseased branches but they looked horrible afterwards. So, we made the difficult decision to remove them all. Now on to replacing the big empty spot.
Photo credits: University of Minnesota ( 1, 2, 3, 6, 7), City of Edmonton (4), Wisconsin Horticulture Extension (5)