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

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.

Abiotic Disorder – The Garden Thyme Podcast

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It has been a weird spring weather wise, and that weird weather may have stressed some of your plants out.  In this months episode we are talking all about abiotic disorder in the garden.  Abiotic disorder in plants are caused by non-living factors such as weather,  and the enviroment .   We will give some examples of what we have seen so far this year,  and what you should be looking for in your garden . 

We also have our: 

  •  Native Plant of the Month  (Bottlebrush grass)at 26:45
  • Bug of the Month (Green Lacewing) at 30:15
  • Garden Tips of the Month at 36:45

 If you have any garden-related questions, please email us at UMEGardenPodcast@gmail.com or look us up on Facebook.

The Garden Thyme Podcast is brought to you by the University of Maryland Extension. Hosts are Mikaela Boley- Senior Agent Associate (Talbot County) for Horticulture, Rachel Rhodes- Senior Agent Associate for Horticulture (Queen Anne’s County), and Emily Zobel-Senior Agent Associate for Agriculture (Dorchester County).

Theme Song: By Jason Inc

Q&A: Why do my hollies and other evergreens have brown and pale leaves?

holly with leaves showing sections of brown and pale color
Winterburn symptoms on holly. Photo: David L. Clement, University of Maryland Extension

Q: Several of our evergreens (different kinds) have brown or pale, bleached-looking leaves. Do they have a disease already, and can anything be done? Is it preventable in the future?

A: Most likely it’s winterburn, especially since most infectious diseases won’t cause symptoms this early and seldom impact several unrelated plants to the same degree. Winterburn is an abiotic disorder or injury – abiotic translates to without (a-) life (biotic) – meaning the condition has a non-living cause. Abiotic plant disorders are environmental, and causes include wind, water, temperature, and soil pH. In comparison, biotic factors would include insects, mites, fungi, or bacteria.

No treatment is recommended because the damage has been done, but winterburn is rarely a serious threat to a plant’s long-term health. As new growth resumes, the plant will eventually shed the damaged leaves. If it’s too much of an eyesore, you can selectively trim away the worst of it this month. Causes for winterburn typically involve a combination of cold temperatures, wind, and exposure to sun. Any autumn pruning that results in tender regrowth is priming a plant for winterburn, which is one reason it’s not recommended.

Why are cold-hardy evergreens damaged? Leaves “breathe” through tiny pores on their surface, and this gas exchange also allows water vapor to leave the leaf. Moisture leaves our bodies the same way – picture foggy breath on a cold day. Breezy days, especially in winter’s drier air, speeds-up this evaporation, as can the sun’s weak warmth. Meanwhile, during cold snaps, moisture in the surface layers of soil freezes, which prevents roots from absorbing it. Since the plant cannot replenish all of the moisture it’s losing, the leaf tissue starts to essentially freeze-dry. A thaw won’t reverse the damage because the cells have been injured, just like skin with frostbite. (Unlike our skin though, which can heal to an extent, leaf tissue can’t repair itself.)

Broadleaf evergreens are more vulnerable to winterburn than needled evergreens because the leaf surface area and evaporation potential is so much greater. Younger plants also have greater vulnerability because they are still establishing roots. This is the main reason it’s risky to plant evergreens late in the fall. Cherry laurel, boxwood, holly, rhododendron, camellia, and southern and sweetbay magnolias are common winterburn victims in our area. Plants kept in containers are also susceptible because their roots dry faster and experience more drastic temperature swings than they would in the ground.

The only actions you can take to minimize winterburn risk is to site evergreens out of the brunt of winter winds and to periodically monitor their root zones for moisture, irrigating when dry during a warm spell. Plants overwintering in pots can be sheltered a bit near a wall or windbreak, but don’t bring them inside as the interruption of dormancy may detriment their health.

Learn more and see additional photos on the Home & Garden Information Center website: Winter Damage on Landscape Plants.

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

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

Why is My Tree (Or Shrub or Flower) Dying? Abiotic Problems Could be the Cause

freeze damage on hydrangea
Hydrangea leaves damaged by a late spring freeze. Photo: D. Ricigliano

Professionals in the landscape and greenhouse industry, trained horticulturists, and Master Gardeners often use the term “abiotic disorder” when diagnosing a plant problem. To the layman, this can be very confusing. To add to the confusion, signs and symptoms you see on your plants can look very similar to the damage caused by insects and diseases.

Surprisingly enough, the vast majority of plant problems are not caused by insect pests or diseases. Typically, the first thought that comes to mind when a plant is looking “ill” is that some insect or fungus has attacked it without much thought that it could be something else.

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