Lilac Care

I can still picture the lilacs that grew in our yard when I was growing up, likely planted by my grandmother. The clusters of lavender flowers had a fragrance that could not be imitated. The oldest known lilacs planted in our country date back to 1750. They are not native to North America. Out of more than twenty species, all but two derive from Asia. The common lilac (Syringa vulgaris) originated in Europe.

Lilacs grow best in full sun and slightly acidic to alkaline, well-drained soil. They may take three to four years to establish, but once they do, they can live for many years. You do not need to fertilize them often. Doing so may result in all foliage and no flowers. To ensure abundant flowering, cut off all faded blossoms to a set of leaves each year. Not doing this will prevent flowering for the following year. Flower buds form the summer before they bloom, so pruning branches later in the year will remove future flowers. The yearly removal of one-third of the oldest stems will prevent your plant from becoming tall and leggy.

Lilacs do not come without issues, though. Powdery mildew is a frequent problem. It is a fungal infection that spreads through spores in the air, thriving in warm, humid conditions. A fungicidal spray is the best time to fight this disease in the initial stages. If it is heavily infected, remove the infected leaves or branches.

Lilac borer is a clear-winged moth that lays eggs at the base of the lilac. The larva will bore into the stems leaving sawdust and sap near the bottom. Pruning out the infected branch will help with this.

Oystershell scale looks like tiny little oysters sprinkled all over the bark. Control these piercing-sucking insects with horticultural oil or pruning out the pests.

Bacterial blight is a blackening of new growth, leaves, and buds caused by Pseudomonas syringae. It also appears as irregular spots on the leaves ringed by yellow halos. A copper spray may help manage during the early spring each year and prevent the problem before the buds open. Prune the infected stem Immediately and destroy all diseased plant parts. Remember to dip your pruners in an alcohol solution between each cut to avoid spreading the infection. Prune only when the weather is dry, with no rain forecast for a few days.

Leaf scorch occurs after excessive rainfall or watering suffocates the root system leaving the plant unable to support itself, causing leaves to turn brown and drop off. Prune out dead branches.

European hornets may strip the bark from lilacs to get the sap underneath and use the bark to make their papery nest. These hornet colonies die off in the winter. The affected branches may be pruned out.

After pruning out unwanted, diseased leaves and branches, dispose of them by burning or placing them in a tied bag in the trash. Do not compost them. The disposal avoids spreading the disease, and if using any pesticide, always read and follow the labeled directions.