by DEBRA MARTIN FEDDERSEN, Winona County Master Gardener volunteer
Lilacs are one of my favorite spring-blooming shrubs with their purple or white flowers and delightful scent, so why were they blooming in late September and early October? In some cases, it could be the variety of lilac that has been planted. There is a variety called the “Bloomerang” lilacs, by Proven Winners, that will re-bloom in August or September. Or, sometimes a Dwarf Korean lilac will re-bloom late. But mostly what I was seeing are the “old fashioned” heritage lilacs that have been planted as hedges or are decades old and are normally the harbinger of spring. Characteristically, the leaves on these fall blooming lilacs were in the process of falling off or have already been dropped.
Lilacs typically will bloom in the spring and will start to set flower buds right after they bloom. If you need to prune your lilac scrubs the best time is right after they bloom. If you prune before they bloom, say March or April, or too late in the summer, you will remove the buds and not get any flowers. Once they have gone through a normal summer, fall and winter, they will bloom the following spring. The trigger to bloom is actually a hormonal response to the weather — the warmer temperatures during the day, cooler at night and the 12 hours or more of sunlight.
This year, the weather (which this fall has been outrageously pleasant!) and the amount of moisture tricked (some may say “stressed”) the plants into thinking they went through a little winter. We’ve had warmer temperatures, but we’ve had cool temperatures, too, so it’s that fluctuating temperature that caused the shrubs to confused the fall for spring and prompted those plants to bloom.
The downside is that the shrubs will have less blooms or no blooms this coming spring. The lilac plants will be just fine and will re-sync in the spring to set buds for the spring of 2023.