lilac

Lilac Rejuvenation by Pruning

Maryland Grows2 Comments

Each year, the spring and summer seasons seem to go faster and faster, and 2024 is no exception. If you have a lilac shrub, you can probably still imagine the sweet fragrance and beautiful flowers from a few months ago. I get several questions each year about lilacs, so the blog today is going to answer some of those inquiries! 

A few years ago, we decided to begin excavating for our new garage in late summer, and unfortunately, had to move a lilac shrub. The transplanting was not as high of a priority as it should have been, and the shrub suffered tremendously the following year. We gave it a season to see if it would recover, but ultimately, it was too damaged. At that point, we decided to try rejuvenation pruning and cut everything back to 6” above the soil line in hopes that the shrub would come back and have a better overall shape and appearance. We had nothing to lose as the plant was suffering, not growing, and not flowering. 

A lilac that was transplanted at the wrong time of the year and damaged. Photo: A. Bodkins, UME

Question:  What is rejuvenation pruning?

Answer: Lilac rejuvenation pruning involves cutting the entire woody shrub back to a few inches above the soil surface. This can be done if a shrub is really scraggly or if you want to change its shape entirely. Last summer, my parents had to do a construction project behind their very large, 20+-year-old white lilac, and they had to cut it back to the ground. It seems to be rebounding just fine, though!

University of Nebraska-Lincoln Extension guidance recommends doing rejuvenation pruning in late winter or very early in the spring.

March 8th: First sign of life on the rejuvenation pruning. Photo: A. Bodkins, UME
a lilac bush that was pruned severely now has new green leaves
June 4th: Regrowth progress. Photo: A. Bodkins, UME

Question: My lilac has not bloomed for the last several years. What could be wrong? It used to be beautiful each spring! 

Answer: Lilacs need full sun to bloom. Often in people’s landscapes, as trees mature, lilacs get less sun than they once did, leading shrubs that once produced abundant, full blooms to have limited to no blooms.

Question: Why did my lilac bloom in the fall?

Answer: Environmental stress can cause out of season blooming. Some examples include drought, excessive heat, defoliation from pests, heavy pruning, insects, or diseases. 

Question: What time of year should I prune my lilac?

Answer: Many spring-blooming, woody shrubs will set the flower buds for the next season’s growth in late spring or early summer, so be sure to prune for shaping and maintenance purposes as soon as the shrub is finished blooming for the current growing season.

For more information on lilacs, see the Home and Garden Information Center’s page, Lilac: Identify and Manage Problems — particularly the sections on diseases, insect pests, and heat-tolerant and powdery mildew-resistant varieties. 

Remember, you can always contact your local University of Maryland Extension office or use Ask Extension to get answers to all your gardening questions.

By Ashley Bodkins, Senior Agent Associate and Master Gardener Coordinator, Garrett County, Maryland. Read more posts by Ashley.

 

Q&A: Why are lilac leaves brown and curling?

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Irregular brown spots and blotches appear on lilac leaves, followed by leaf curling and defoliation in late summer. Photo: UME Ask Extension

Q: My lilacs look like death-warmed-over this time of year. Do you know what’s wrong, and is there anything I can do at this point?

A: Lilacs are sadly not very well-suited to our mid-Atlantic conditions. We’re at the southern edge of their heat tolerance, so while they weren’t among the best flowering shrub choices to begin with, climate change is only going to worsen their prognosis. Several types of leaf-spotting fungi and bacteria, plus general heat stress (which also increases their vulnerability to borers), results in foliage that looks quite beat-up by late summer. Brown spots, crispy leaf edges, and bare stems from premature leaf drop are all typical. You can explore lilac ailments and their management on our lilac diagnostic page.

No fungicide will reverse these symptoms once they appear, and while they might work as a preventative if applied before bud-break (and re-applied repeatedly well into the summer), it’s simpler to just grow something else if a plant is going to be that much of a hassle. This is especially true if the treatments don’t work and the plant still winds up looking horrible. Fungicides also carry the risk of harming other organisms.

For now, you can rake up and dispose of any fallen leaves, though this isn’t a foolproof way of removing a source of infectious spores. Cut down the oldest, thickest stems this winter (they tend not to bloom well at that age anyway) and open up the canopy by selectively removing some stems that contribute to foliage crowding. You can do this thinning after bloom next spring.

For anyone really wanting to grow lilac despite these challenges, try cultivars with above-average disease resistance and heat tolerance. While not immune to problems, they perform much better, even if they don’t look exactly the same or have blooms as large or heavily perfumed. ‘Miss Kim’ is a round, compact-growing cultivar with pale lavender-purple flowers that’s been around for decades. Other varieties are now available with pink or deeper purple blooms, some of which even rebloom a bit, sporadically producing flowers into summer and early autumn, though high heat could still hamper that.

dwarf lilac with lavender flowers
Dwarf lilac species and hybrids handle Maryland conditions much better than the traditional varieties. Some recent introductions will also re-bloom sporadically later in the summer. Photo: M. Talabac

All lilacs, but especially the traditional, classic “French” types, should be planted in a location with great air circulation (so, not up against a fence or wall) so wet leaves dry quickly after rain, dew, or irrigation. Wet foliage is more easily infected by pathogens.

The main perk of growing lilacs is fragrance, so if you want a scented replacement, consider: Winterhazel (Corylopsis), Koreanspice Viburnum (Viburnum carlesii) and its hybrids, Summersweet (Clethra), Seven-son Flower (Heptacodium), Carolina Allspice (Calycanthus), various deciduous Azaleas (Rhododendron viscosum and several others), Mockorange (Philadelphus), and Fragrant Abelia (Abelia mosanensis). Their scent characteristics, flower colors, mature sizes, and preferred growing conditions may differ from lilac, but nothing is going to be an exact substitute. Plus, several of these species will offer the additional bonus of showy autumn foliage or (for the native ones) better wildlife value. These are just some shrub ideas; there are also fragrant perennials and, if you have the room, several fragrant trees.

By Miri Talabac, Horticulturist, University of Maryland Extension Home & Garden Information Center. Miri writes the Garden Q&A for The Baltimore Sun. Read more posts by Miri.

Have a plant or insect question? University of Maryland Extension has answers! Send your questions and photos to Ask Extension.