Author:Christa

Free the Flare: Maintain Visible Root Flare for Tree Health

January 12, 2024January 12, 2024Maryland Grows4 Comments

Tree planting efforts are picking up as Maryland’s 5 Million Trees Initiative moves forward in 2024. Getting these trees – any landscape trees – off to a good start at planting time and through their first few years of establishment is important for their long-term growth and benefits to the environment.

At Ask Extension, we often receive photos of newly planted trees and older specimens with signs and symptoms of trouble. One of the things we do in our diagnostic process is look to see if there is a “root cause.” Is a girdling root present at the base of the tree trunk? Is the tree planted too deeply? Can we see a root flare? Today I want to bring these questions to the surface and explain why an exposed root flare can help prevent the formation of girding roots and why it matters for tree health and pest management.

a beech tree with a nice sloping visible root flare above the soil line — A beech tree with normal, healthy root flare. Photo: Miri Talabac, University of Maryland Extension (UME)

What is a root flare?

The root flare is the area at the base of a tree trunk where the topmost roots emerge outward. This area is sometimes referred to as the trunk flare or root crown. In many species of trees, the trunk widens and curves outward (“flares”) like the base of a wine glass. This is illustrated nicely in this brief video by the University of Maryland Arboretum and Botanical Garden’s Outreach Coordinator, Meg Smolinkski.

What is the root flare of a tree?

When thinking about the trunk and root system of a tree, it is important to keep in mind: Roots need to be in the soil to get a steady supply of moisture and nutrients. The trunk (stem) portion should be out of the ground where exposure and good airflow help to keep the bark dry.

In our landscapes, we have many trees that are planted too deeply and the root flare is not visible at all. The trunks go straight into the ground like telephone poles. This can result in lower bark rotting, reduced oxygen supply to the roots, disease and pest problems, and girdling roots.

We have an epidemic of planting trees too deeply

At the University of Maryland Extension Advanced IPM Conference for the commercial horticulture industry last month, Jacob Hendee, an arborist for the Smithsonian Institution Gardens, talked about how common it is nowadays to see trees planted too deeply. Burying the root flare has reached “epidemic” proportions in our landscapes, he noted – and it is killing trees.

The main problem he addressed in his talk was that buried root flares can set the stage for stem girdling roots to develop unnoticed. Stem girdling roots (SGRs) grow around the tree’s base, rather than pointing outward away from the trunk as normal roots should. As girdling roots grow and enlarge, they compress the water- and nutrient-conducting tissues in the tree. This interrupts normal plant functions and can lead to symptoms such as leaf yellowing (chlorosis), smaller-than-normal leaves, leaf scorch (browning), branch tip dieback, and bark cracking. SGRs can and do result in overall tree decline and eventual failure.

girdling roots are present at the base of a tree that has too much mulch — An example of girdling roots. Photo: M. Talabac, UME

An illustration showing the growth of sapwood in a tree - In year 5 it is all sapwood, in year 10 the sapwood outlines the heartwood and in year 15 there is a larger ring of sapwood on the outside circumference — Looking at a cross-section of a tree trunk, the light-colored portion is the water-conducting sapwood (xylem). Source: Jacob Hendee, Smithsonian Gardens

An illustration showing how a stem girdling root grows around a trunk and constricts - limits the growth of the water conducting xylem ring — When a stem girdling root forms around the trunk of a tree (represented in orange in the diagrams), it compresses and kills the water-conductive sapwood, which can result eventually in a dead tree. Source: Jacob Hendee, Smithsonian Gardens

Trees under moisture stress due to stem girdling roots become more susceptible to pests and diseases. Scale insects are significant pests of some landscape trees, as are some types of beetles and other insects. If a tree develops a pest issue, the pest may be secondary to the problem that made the tree vulnerable to the pest in the first place – stress.

Hendee emphasized that maintaining a visible root flare and preventing SGRs are practices of Integrated Pest Management (IPM). IPM involves using physical, cultural (plant care), and biological methods to manage pests and diseases, leaving chemical pesticides as a last resort. In the example of tree care, correct planting and monitoring to prevent stem girdling roots are key steps to preventing tree stress. Instead of thinking about killing secondary pests that show up on trees, think about how to prevent stressful growing conditions from the beginning and during the life of a tree. Trees with minimal stress are more resilient to insect pests and less likely to be overwhelmed by them or need intervention to recover.

How do stem girdling roots get started?

Hendee noted that plant care practices, both before planting (at the nursery), during planting, and afterward (over-mulching) contribute to this problem.

1. Many trees are grown too deeply in the nursery. Girdling roots can start to form inside nursery pots when the roots hit the container and start circling. This issue can worsen when young trees are moved into larger containers as they grow (such as saplings being transplanted into a bigger pot as they mature) and their roots are not loosened or pruned to correct deformities. Larger trees are sometimes planted too deeply in the nursery field and come to the customer in “ball and burlap” form with the root flare already covered in soil.

2. Many trees are planted too deeply at the time of installation. If the planting hole is dug too deeply, the root flare gets buried when the soil is filled back in, and often then further covered with mulch. In that situation, stem girdling roots can develop and worsen undetected.

3. Tree flares are often buried deeply in mulch. Too often we see huge piles of mulch – sometimes one foot high or more “mulch volcanoes” – around trees. This will keep the bark moist and can encourage new roots to sprout from the trunk above the main supporting roots (the flare). Those adventitious roots will grow upward for oxygen and may begin to girdle the flare and trunk. They will also be more vulnerable to moisture stress since the mulch does not retain water in the same way soil does. There is absolutely no horticultural basis for putting a big mound of mulch around a tree like this!

Mulch piled over 1 foot high around a young tree near a parking lot - there is no visible root flare - this is a mulch volcano — An example of incorrect mulching. Photo: Dr. David L. Clement, UME

mulch was incorrectly placed on top of a girdling root around the base of a tree — Here fresh mulch was incorrectly placed on top of a girdling root and up against a tree trunk. Photo: C. Carignan, UME

What can you do? “Free the Flare”

1. Check the roots at planting time.
If you purchase a container-grown tree, ensure it is free of circling roots inside of the pot. If you do find roots that are circling the root ball, cut through those roots with a pruner or other sharp tool. Set the roots in the planting hole so that they are pointing in an outward direction.

Prevent girdling roots when planting a container-grown tree

2. Keep the top of the root flare visible.
Root flares should be above the soil line. Plant so the root flare is 2 to 4 inches above grade. When purchasing a container-grown or burlapped tree, you may need to wash away some of the soil to see where the root flare begins. If a landscaper is installing a tree for you, make sure they set the tree at the correct depth.

soil from a container-grown tree was washed away to reveal that the top of the root flare had been sunken too deeply in the pot — A hose was used to wash away the soil from a container-grown tree, revealing the top of the root flare. The difference in the lower bark color (on the trunk) indicates that the plant was several inches too deep in its container. Photo: M. Talabac

When a root flare is visibly present, it can help deflect any stem girdling roots that begin to grow, forcing them away from the trunk. It also makes it easier to see where girdling roots begin to form. Monitor the root flare area of your tree(s) regularly and cut through any circling roots that begin to grow. It is easier to cut wayward roots when they are small. The process of locating and remediating stem girdling roots on older trees can be very expensive.

Also note that some species of trees are more prone to developing girdling roots (e.g., maples), and sometimes girdling roots develop below the soil surface where they are not easily detectable except by above-ground clues. If you see symptoms of water stress in the canopy of an otherwise sufficiently-irrigated tree (e.g. leaf scorch, smaller-than-normal leaves), consult with a certified arborist for a tree assessment.

3. Don’t overdo it with the mulch!
Keep a mulch-free buffer zone around the root flare. Hendee suggested leaving a 3 to 12-inch area bare around the base of the tree. Think of it as a donut hole: mulch should be laid down in the shape of a wide, shallow donut rather than a big heaping mound. The total depth of the mulch should be only about 2 to 4 inches.

how to mulch correctly - free root flare - mulch free buffer around the base of the trunk - 2-4 inches of mulch depth - broad mulch width — Mulch applied correctly. 1 Free root flare, 2. Mulch-free buffer around the root flare, 3. 2 to 4 inches mulch depth, 4. Broad mulch width. Infographic by Smithsonian Gardens

For further exploration of these topics and correct tree-planting procedures, I recommend the following resources:

Show Me Your Root Flare (PDF) | Clemson University

Girdling Roots | University of Maryland Extension

Planting and Care of Trees | University of Maryland Extension

Problems With Over-Mulching Trees and Shrubs | Rutgers

By Christa Carignan, Certified Professional Horticulturist & Coordinator, University of Maryland Extension Home and Garden Information Center. Read more posts by Christa.

Illustrations used with permission from Jacob Hendee, Smithsonian Gardens

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Make and Plant a Bucket Garden

August 11, 2023August 10, 2023Maryland Grows2 Comments

If you don’t have space for an in-ground garden or access to a community garden, planting in 5-gallon containers can be a great option for making a “bucket garden” along a sunny walkway, balcony, or porch. In this video, Extension Specialist Jon Traunfeld demonstrates how to make a self-watering container garden using 5-gallon buckets and a few basic materials. You can get these buckets for free from restaurants, bakeries, and grocery stores. They are used for shipping food products and then they are usually thrown away afterward. This is a great way to give them a second use!

Tomatoes, peppers, and basil are some of the most popular plants to grow in a bucket garden. It is too late to start those plants this season, but in late summer, you can still plant kale and other leafy greens, carrots, beets, and perennial herbs. Use our Vegetable Planting Calendar as a guide.

Instructions for the self-watering bucket garden are also available on the University of Maryland Extension website, on the self-watering containers page.

By Christa K. Carignan, Coordinator, Digital Horticulture Education, University of Maryland Extension Home & Garden Information Center. Read more posts by Christa.

What’s Eating My Rose Leaves?

June 16, 2023June 16, 2023Maryland Grows1 Comment

roseslug sawfly damage on rose — Roseslug sawfly damage on rose. Photo: UME/Ask an Expert

Q: My rose leaves have white spots and holes in them. What causes this and how do I treat it? Is there a natural remedy that does not involve powerful chemicals?

Answer: It looks like your rose has symptoms of sawfly damage. Check the undersides of the leaves and look for tiny green larvae that look like little worms or caterpillars. These are the juvenile stage of an insect called roseslug sawfly.

Roseslug sawflies are neither slugs nor flies. They belong to the same order of insects as wasps, bees, and ants (Hymenoptera). Adult female sawflies use their unique ovipositor (egg-laying part) to saw a small slit in a leaf or stem where they lay their eggs. When the eggs hatch, the larvae feed on the leaf surfaces and cause an etched or scratched appearance. Some roseslug larvae chew through the leaves entirely. Damaged foliage turns brown and curls up as the season progresses.

bristly roseslug on rose leaf — Bristly roseslug *(Cladius difformis).* Photo: Whitney Cranshaw, Colorado State University, Bugwood.org

bristly roseslug sawfly adult — Bristly roseslug *(Cladius difformis)*, adult stage. Photo: Whitney Cranshaw, Colorado State University, Bugwood.org

In Maryland, there are three species of roseslug sawflies that cause damage to roses: the bristly roseslug sawfly, the roseslug sawfly, and the curled rose sawfly. Most of the feeding activity on roses in Maryland is seen in May and June, but some sawfly larvae can continue to be active until fall. Other insects, such as Japanese beetles, also cause chewing damage on rose foliage (typically in June-July).

rose-brown-leaves — Browning and leaf curling from rose slug sawfly damage. Photo: UME/ Ask an Expert

The best way to manage roseslug sawflies without chemicals is to monitor your plant(s) for damage symptoms early in the season (start looking in May) and manually remove any larvae (squish them or pick them off and discard them). A forceful spray of water from a garden hose targeted toward the leaf undersides can also get them off. Once dislodged, they cannot climb back up into the plant. Horticultural oil and Spinosad also work well against sawflies. Read and follow the product label instructions for the correct application procedures.

Two sawfly larvae are present on the undersides of rose leaves. Photo: C. Carignan

Predatory insects and birds help to manage sawfly populations naturally. Adding more flowering plant diversity to your landscape will provide food and habitat for beneficial animals that in turn help to reduce future pest problems.

Rose shrubs usually recover from sawfly damage eventually, as long as they are not struggling from other ailments or stressors such as drought.

Additional Resources

Sawflies | UME Home & Garden Information Center

Rosie Defoliators | Bug of the Week, University of Maryland, Department of Entomology

By Christa Carignan, Maryland Certified Professional Horticulturist, Coordinator, University of Maryland Extension Home & Garden Information Center. Read more by Christa.

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

Great Grasses for Maryland Landscapes

March 13, 2020August 18, 2022Maryland GrowsLeave a comment

What are some beautiful plants that are relatively easy to maintain and unappealing to deer? Take a look at the ornamental and native grasses!

Ornamental grasses are plants that provide year-round beauty, texture, persistent ground cover, erosion control, and a variety of additional benefits. They are:

Available in many heights and forms suitable for different landscape situations
Helpful in trouble spots like slopes or places where a living screen is desired
Relatively easy to maintain by pruning back once each year
Generally distasteful to deer.

If you are planning to add native plants to your landscape, add a few grasses to the mix. Grasses provide winter shelter for beneficial insects and seeds for birds. Some even have interesting associations with small butterflies called skippers. For example, the Leonard’s Skipper uses little bluestem, switchgrass, poverty oatgrass, and bentgrass as host plants. That means that when these insects are in their juvenile stage (caterpillars), they can only feed on these types of grasses to survive. As adult skippers, they fly off to feed on the nectar of other flowering plants. They are delightful to watch “skipping” around a butterfly garden!

ornamental grasses in winter — Ornamental grasses provide textural interest in a garden in the winter. Here they are beautiful in combination with remnant seedpods and the red berries of winterberry holly in the background. Photo: C. Carignan

There are about 350 species of grasses in Maryland. They are the primary plants found in native meadows and there are even grasses, such as Eastern bottlebrush grass (Elymus hystrix), that thrive in our state’s shaded woodland areas.

Eastern bottlebrush grass *(Elymus hystrix)* Photo: Chris Evans, University of Illinois, Bugwood.org

The Maryland Native Plant Society has named 2020 “The Year of the Grasses”. All year long, through their monthly events and plant walks, you can learn about Maryland’s grasses and their native habitats.

Ornamental and native grasses are readily available at garden centers and native plant sales. Be sure to avoid invasive ones like Chinese silvergrass (Miscanthus sinensis).

switchgrass — Switchgrass *(Panicum virgatum) ‘*Shenandoah’. Photo: Mikaela Boley

For some great choices, check out my colleague Mikaela Boley’s excellent guide to Ornamental and Native Grasses for the Landscape on the Home & Garden Information Center website.

If you already have ornamental grasses in your landscape, now is a good time to prune them. Grasses that turn brown in the winter should be cut down to about 2″ above the ground in early spring before new growth begins.

By Christa K. Carignan, Coordinator, Digital Horticulture Education, University of Maryland Extension Home & Garden Information Center. Read more posts by Christa.

Helen’s flower hails pollinators

February 3, 2020September 15, 2022Maryland Grows2 Comments

common sneezeweed flowers — *Helenium autumnale.* Photo: Beverly Turner, Jackson Minnesota, Bugwood.org

Helen’s flower is an underdog when it comes to native plants. It is not as well known or as popular as butterfly milkweed, bee balm, or black-eyed Susans — but perhaps it’s time for its day in the sun. It makes a nice addition to a pollinator garden.

Helenium autumnale is the species name of this North American native perennial plant. It goes by the (somewhat unfortunate) name of “common sneezeweed” because dried parts of the plant were formerly used for making snuff to induce sneezing. As an ornamental garden plant, it is not known to prompt sneezes from pollen dispersal (it relies on insects for pollination) and I prefer to address it by its lovelier common name, Helen’s flower… or just plain Helenium.

Wild Helenium autumnale boasts cheerful yellow button-like flowers tended by a skirt of turned-down petals in late summer to fall. Its natural habitat in Maryland includes swamps and moist riverbanks, so in your garden, it will like a location where it has some regular soil moisture. It can grow in full sun or partial shade and stretches in height from 2 to 5 feet tall. The flowers support a variety of pollinators such as bees, wasps, syrphid flies, butterflies, and beetles.

A wide variety of cultivars of Helenium are now available. They range in color from bright canary yellow to orange and crimson and various combinations in between. Many of the cultivars tolerate drier soil and have a more compact habit.

Mt. Cuba Center in Delaware conducted field trials of 44 Helenium species and cultivars from 2017 to 2019. They evaluated plants for their habit, vigor, disease resistance, floral display, and pollinator visits.

helenium flowers in a garde — *Helenium flowers in a garden, “The warm glow of early Autumn” by hehaden, Flickr*

Given the high interest in pollinator gardens right now, I was curious about their observations of pollinator visits in particular.

The native Helenium autumnale had the most observed pollinator visits (162), while the cultivar H. ‘Zimbelstern’ came in second (151). Both of these had excellent powdery mildew resistance as well. Other cultivars such as Helenium autumnale ‘Can Can’ and H. ‘Tijuana Brass’ also had excellent ratings for these two characteristics. The best performers in the study overall (considering all the characteristics evaluated) were ‘Kanaria’, ‘Zimbelstern’, and ‘Can Can.’

The native Helenium autumnale had the most observed pollinator visits (162), while the cultivar H. ‘Zimbelstern’ came in second (151).

For all the details and results of the evaluation, read the report online.

If you plan to start (or add to) a pollinator garden this spring, do consider adding Helen’s flower if you have a moist site in full sun or partial shade. Mt. Cuba’s report provides good information on plant care, including staking and pruning tips and recommendations for managing the two most common diseases — powdery mildew and aster yellows.

To purchase plants, check the Maryland Native Plant Society’s website for spring native plant sales and nursery sources.

Visit the Home & Garden Information Center website for additional resources on native plants and gardening for pollinators.

By Christa K. Carignan, Coordinator, Digital Horticulture Education, University of Maryland Extension Home & Garden Information Center. Read additional posts by Christa.

Q&A: Can you recommend apps or websites for plant identification?

December 9, 2019December 9, 2019Maryland Grows2 Comments

taking a cell phone photo of a plant — *A well-focused photo of a flower can be uploaded to an app for identification. Photo: Dan Adler*

Q: Can you recommend apps or websites to help with plant identification?

A: The Picture This app does a good job with basic plant identification and works both on iPhone and Android. Take a good clear photo of any distinguishing features of your plant (e.g., flowers, fruits, leaf arrangement) for the best results. When you upload your photo to the app, it uses artificial intelligence technology to compare the details of your plant to those in its database of 10,000+ species. It will come up with the most promising matches within seconds.

In my experience, Picture This is not always accurate, but it does well most of the time. It is the best app I have found for plant identification. It will often get you to the correct plant family or genus, if not the exact species. The app also provides information about growing conditions and care tips for your plant.

Another good app is iNaturalist. This app was developed jointly by the California Academy of Sciences and the National Geographic Society and also works both on iPhone and Android. It has a large community of users, including scientists who contribute to it and use some of the data for their research.

taking a photo of a leaf with phone

Similar to Picture This, you can submit your photos to iNaturalist and the app searches a database to find the best match. You also can crowdsource an answer by asking for help from people who use the app. Knowledgeable members of the iNaturalist community will identify and verify your observations. In addition to plants, iNaturalist identifies insects, birds, other animals, and even fungi.

There are basic videos online to help you learn how to use the features of iNaturalist. Some nature centers and community groups occasionally offer hands-on workshops to learn and practice using the app. For example, if you are in the vicinity of Montgomery County, Maryland, the Maryland Native Plant Society’s January 28, 2020, meeting in Kensington will focus on how to use some of the more advanced features of iNaturalist (Discover the Full Capabilities of iNaturalist).

In my experience, Picture This has been more accurate with plant identification whereas iNaturalist is stronger for identifying insects and other animals. Since these tools are still developing, it is a good idea to check the results with another reference to verify the identification. For example, you can submit your photo(s) to the Home and Garden Information Center’s Ask an Expert team if you would like further assistance or more information about our local plants in particular. As more people use and contribute to plant identification apps, surely they will improve and become more refined.

potted plant and a laptop computer

There are also several Facebook groups that are helpful for identifying plants. The ones I have found most useful are Plant Identification, Maryland Native Plant Society Discussion Group, and Capital Naturalist. There are many others. In your Facebook account, find the Groups section and search for your topic of interest, whether it be houseplants, trees, flowers, or something else. There are groups for everyone and you can use them to crowdsource an answer or simply follow along and learn more about your subject of interest. Be sure to read and follow the rules of the groups you join.

Have fun, plant explorers!

By Christa K. Carignan, Coordinator, Digital Horticulture Education, University of Maryland Extension Home & Garden Information Center

Q&A: What is this white growth on my cherry laurel shrub?

September 25, 2019February 15, 2024Maryland Grows4 Comments

*An infestation of white prunicola scale on cherry laurel. Photo: University of Maryland Extension*

Q: We have cherry laurel shrubs that were growing very well for a few years. Yesterday, I noticed some of the leaves on one side of a laurel were brown. When I looked closer, I found that all of the branches inside were covered with a white substance. What is it? What can I do about it?

Answer: The white substance on the branches is an infestation of white prunicola scale. Scales are very tiny insects that feed on plant sap. Their feeding leads to leaf yellowing, browning, and eventual dieback of branches.

Scale insects are challenging to manage. The waxy white substance they produce provides a form of protection from desiccation and predators. They produce three generations each year, so if a population is not controlled all at once, they can continue to reproduce and be a persistent problem.

When there is a heavy infestation of white prunicola scale and dieback is severe, it may be best to remove the shrub altogether rather than try to treat it. Depending on where the infestation is located, you may be able to prune out branches selectively and discard them.

Fertilized female scales overwinter on the bark of the branches, so another step in management is to apply a dormant rate of horticultural oil during the dormant season (when deciduous plants have lost their leaves). You can first use a soft-bristled brush to scrub off the scale patches gently. Then apply the horticultural oil.

If female scales remain on the shrub, juveniles (called “crawlers”) will emerge in the spring. Crawler periods vary from year to year depending on temperatures. For this species, new generations may be out in May, mid-July to mid-August, and September.

The tiny juvenile crawlers are salmon-colored. You can place a simple trap to detect their activity; wrap a piece of double-sided tape around a few branches. When you see crawlers stuck to the tape, that is the ideal time to apply horticultural oil. Oil spray is the least harmful to beneficial insects such as ladybird beetles, which you want to keep in your landscape because they help tamp down on other pests.

White prunicola scale is a fairly common problem on cherry laurels. Residents who have these shrubs should check them periodically for leaf yellowing and white spots on lower branches. Scales are easier to manage if you catch them early.

By Christa K. Carignan, Maryland Certified Professional Horticulturist, Coordinator, University of Maryland Extension Home & Garden Information Center

More on this topic: Cherry Laurel: Identify and Manage Problems, from the University of Maryland Extension (February 2024)