Plant and Protect

Expert Advice

The Plant Clinic is a leading source of science-based advice about trees, plants, and landscapes.

Content Detail

The Morton Arboretum’s Plant Clinic is a leading source of science-based advice about trees, plants, and landscapes, helping gardeners and landscape professionals throughout the Chicago region and the world have healthy, attractive, well-chosen plants.

Trained staff and volunteers are available by phone or by email to help with tree and plant selection, identifying and coping with pests and diseases, and other concerns.

The Plant Clinic also accepts samples for assesment, though it does not have a laboratory on-site. Plants requiring lab testing should be sent to the University of Illinois Plant Clinic Extension.

With advice based on research and nearly a century of experience in caring for a wide variety of trees and plants in the Midwest, the Plant Clinic helps promote sound management practices.

Often the Plant Clinic staff can direct guests to mature plants on the Arboretum’s grounds, which can be a great help in choosing the most appropriate plant for a yard or landscape.

The Plant Clinic also has many online resources to help with trees and plants.

For service on weekdays, you may visit the Plant Clinic lobby in person Monday through Friday, between 10:00 a.m. and 4:00 p.m., or call 630-719-2424 from 11:00 a.m. to 4:00 p.m. with questions. You can also email your plant care questions to plantclinic@mortonarb.org at any time.

Plant Clinic Sponsor

At any season of the year, the Plant Clinic is ready to help gardeners and landscaping professionals have lovely and useful gardens and healthy trees and plants.

The staff and volunteers can recommend good trees, shrubs, and other plants for particular conditions; identify plants; and help with questions about insects and pests, soils, pruning, weeds, and many other topics. They can refer callers to a lab for soil testing or help them find a certified arborist through the Illinois Arborist Association.

Here are some tips on how to make the most of a call or e-mail with the Plant Clinic:

  • If possible, know what kind of plant you’re talking about. Be as specific as you can. For example, it’s more useful to say you have a yew or an arborvitae than to say you have an evergreen. If you have the tag that came with the plant, have it handy.
  • If you don’t know what kind of plant it is, examine it closely and be ready to describe it in detail—not just leaves or flowers, but stems, bark, and branches. Taking a photo that you can email or bringing in a sample will help enormously with identification.
  • To help with identification, show samples of different plant parts—the flowers or nuts, for example, as well as the stem and leaves. How the leaves grow on the stem is important information, so take a photo of a twig with leaves attached.
  • Be ready to describe the conditions the plant is growing under. How many hours of sun does it get? How close is it to a sidewalk or driveway? Do you water it? Do you fertilize it? Can you remember when, how much fertilizer you used, and what the formula was? Have you used any chemicals on the plant? How old is the plant? What grows near it?
  • Think about conditions farther afield. Has a neighbor sprayed or treated his lawn? Has there been construction next door? Is your road salted in the winter? The effects of some stresses, such as road salt or drought, may not show up in a tree or shrub for months or years, so try to remember back a while.
  • When you seek a recommendation for a tree or shrub to plant, make a note of the conditions it will grow under, such as sun and soil, and the available space. Be sure to consider if there are overhead utility lines. The Plant Clinic can help you choose a plant that will suit your needs and thrive in your conditions.
  • Find an extensive library of tree and plant advice on the website or see the Tree and Plant Finder to learn about specific plants.

Frequently Asked Questions

Spring

  • Pruning heavily at planting time is no longer recommended. There are two exceptions: bare-root plants and plants you dig yourself to move to another area. Removing crossing and damaged branches will allow more energy to go into making roots and not leaves, which will reduce the water requirements for transpiration during the first season. Be sure to monitor watering needs if soil becomes dry.

  • The leaf disease called apple scab is caused by a fungus. Cool, moist growing seasons favor this disease. Crabapple varieties differ in their resistance to this disease. Fungal spores infect the leaves in early spring, just as the buds are opening. As the leaves expand, they become spotted and scabby. Severe infections can cause the leaves to drop prematurely (and may also infect fruit and twigs). A couple of years of defoliation will not hurt an otherwise healthy tree but repetitive attacks year after year can weaken the tree and leave it vulnerable to insects and other diseases and eventual death.

    Management of the disease includes cleaning up infected leaves that have fallen to the ground. The fungus can over winter in these leaves and then infect new leaves in spring. Fungicide sprays are available, but must be applied in spring as new leaves emerge, and repeated at labeled intervals. There are a number of excellent varieties of crabapples resistant to apple scab.

  • Before moving any tree it is important to consider that any tree taller than 8 feet, or with a trunk larger than 2 inches in diameter, is difficult to move without special equipment.  If a plant is movable, the best time to move it to a new location is in early spring, while the plant is dormant. Moving a plant while it is actively growing will diminish its chance of survival. This is particularly true of conifers, which have only one growth spurt a year.

    Moving a tree to a new location will require trenching, digging, and severing its roots. Several days before digging, water the plant to ensure moist soil. Moist soil will hold together in a ball and adhere to roots better than dry soil.

  • This is a very common question with many plants. There may be numerous reasons why your plant will not flower. First, age may be a factor. Many woody plants go through a vegetative phase of growth before they produce flowers. This juvenile stage can last anywhere from 2 to 10 years, depending on the species. Crabapple, wisteria, and lilac are some of the more common plants that can go through this phase.

    Temperature can have an effect on flowering plants. Sometimes a plant may survive the winter only to have its flower buds damaged by a late spring frost. Inadequate snow cover may not provide the insulation some plants need, causing damage to flower buds.

    Pruning at the wrong time of year can eliminate spring flowering. Most spring-flowering shrubs form their flower buds in late summer and early fall. Pruning anytime during this period will remove the flower buds. The best time to prune spring-flowering shrubs is just after they finish blooming. Also, as shrubs age, older stems should be removed to allow younger stems to grow, which results in a more vigorous and better flowering shrub.

    Finally, consider the growing conditions for your particular plant. Plants in need of full sun will flower poorly if grown in the shade. Fertilization, especially with excess nitrogen, will promote vegetative growth instead of flowers.

  • You might not be doing anything wrong. Eastern redbud (Cercis canadensis) is a 20 to 25 feet high native tree that occurs over an extended range of the Eastern United States. Plants that are grown from a southern genetic source are not as cold hardy as a plant that has been grown in northern areas. It is recommended to purchase redbud trees originating from a northern source.  Eastern redbud grows best in a moist, well-drained soil in part shade or full sun with adequate moisture. Plants do not tolerate standing water.  They will benefit greatly with a 3- to 4-inch layer of organic woodchip mulch.

  • Plants that will grow in dry shade include red chokeberry (Aronia arbutifolia), common sweetshrub (Calycanthus florida), gray dogwood (Cornus racemosa), American hazelnut (Corylus americana), St. Johnswort (Hypericum), Virginia sweetspire (Itea virginica), spicebush (Lindera benzoin), bayberry (Myrica pensylvanica), nine bark (Physocarpus opulifolius), jetbead (Rhodotypos scandens), wayfaringtree viburnum (Viburnum lantana), and blackhaw viburnum (Viburnum prunifolium). All plants should be monitored for watering needs in dry periods and will benefit from a layer of organic mulch.

  • Yes, there are several clinging vines that will attach themselves directly to a surface by means of holdfasts (adhesive discs) or small aerial roots. They work best on a rough surface such as stone, wood, masonry walls, and tree trunks.  Trumpet vine (Campsis radicans), climbing hydrangea (Hydrangea anomala ssp. petiolaris), bigleaf wintercreeper (Euonymus fortunei), English ivy (Hedera helix), Virginia creeper (Parthenocissus quinquefolia), and Boston ivy (Parthenocissus tricuspidata) will all attach to a brick wall.

  • Select a sunny spot, protected from wind.  The more sunlight, the longer butterflies will stay to find food, shelter, and mate.  Some shade is important for resting in the heat of the day. Choose a mixture of perennials and shrubs to provide a continuous source of nectar for your butterflies. Suggested shrubs include: butterfly bush, blue spirea, cotoneaster, deutzia, hazelnut, New Jersey tea, St. Johnswort, sumac, and weigela.  Suggested perennials include: bee balm, butterfly weed, catmint, chives, coneflower, daisy, daylily, gayfeather, Joe Pye weed, mint, phlox, thistle, verbena, and yarrow.

  • Major tree roots often grow within a few inches of the soil surface. Some species, such as maples, grow roots particularly close to the surface. Removing these roots may disrupt the moisture supply to the tree, causing serious stress. Covering them with soil could cut off the oxygen supply to the fine roots in the soil below. Both situations could lead to decline. The best solution is usually to mulch the area under the tree with compost or wood chips. These materials are porous enough to allow sufficient oxygen supply to the soil and may actually encourage fine root growth.

  • Yes if you want to protect your tree. Emerald ash borer populations are still high in some areas. Where populations have declined the beetles are still able to fly to noninfected trees. Trees exhibiting more than 40 percent decline are not likely to recover. Trunk injections with Emamectin benzoate (Tree`Age) provides at least two years worth of EAB control to large trees under high population pressure.

  • Dormant oil is a heavy-weight horticultural oil used to smother over-wintering insects. It does not work on all insects; however it will work on soft scale species such as magnolia scale. To be effective it should be applied in early March, when temperatures remain above 40 degrees and more important, before leaves start to emerge.

Summer

  • No treatment is necessary. What you see are plant galls, which are swollen, abnormal growths that appear on the leaves, twigs, and flowers of many plants. They will not seriously affect the health of your oak. Most galls are caused by chemicals produced by small insects, such as mites or aphids, during egg-laying or feeding activities on the leaf buds. These chemicals cause plant cells to swell, creating the galls. The insect may live inside the gall for a brief period before completing its life cycle.

  • A mild infestation of Japanese beetles can be controlled by picking them off the plant and dropping them into a container of soapy water. A strong spray of water into trees can get them to move elsewhere. Avoid using pheromone traps; Japanese beetles are flying insects and the traps will bring in more beetles than they catch. Chemical sprays for Japanese beetles can be harmful to beneficial insects and are not recommended. Soil insecticides provide short-term control if applied mid-August through September.

  • Ideally mulch should only be 1 to 3 inches deep on the soil surface above the root system. Applying more than 4 inches may injure plants by keeping the soil too wet and limiting oxygen to the plant roots. Keep mulch away from the base of plants, and do not let it rest against the bark. Around individual plants mulch should form a donut shape, not a volcano.

  • The yellowing of leaf tissue due to the lack of chlorophyll, the green pigment in leaves, is known as chlorosis. Symptoms of chlorosis can vary depending upon the cause, but generally leaf tissue will turn a yellow-green while the veins remain green. Symptoms can appear over the entire tree, but may be more severe on one portion of the tree than another.

    A major cause of chlorosis in the maples is a deficiency of manganese. Although not actually lacking in the soil, these nutrients become unavailable to plants where the soil is heavy and alkaline (pH above 7.0). Other possible causes of chlorosis include poor drainage, damaged roots, grade changes, or compacted soil.

    Management for chlorosis symptoms varies with the cause, but the most lasting results are obtained by improving the tree’s rooting environment. Apply a 1- to 2-inch layer of organic compost (e.g., leaf mold) to the soil surface, followed by 3 to 4 inches of organic mulch (e.g., wood chips). Be sure to water during drought periods to minimize stress.

    While there are several effective treatments available, they may have to be used annually. Soil fertilization treatments produce the best results, but are usually the slowest to respond. Soil treatment is best done in early spring through mid-May. For mildly chlorotic trees, fertilize with a nitrogen or nitrogen- and sulfur-based fertilizer.

  • Dutch elm disease (DED) is one of the most serious diseases to affect American elm (Ulmus Americana) and has killed thousands of elms across the United States. Prevention and early detection continue to be the keys to protecting elm trees from Dutch elm disease. Many of the new cultivars available in the nursery market are resistant but not immune.

    The disease is caused by the fungus Ophiostoma ulmi. It can be transmitted by two species of the elm bark beetle that carry the fungus from an infected tree to a healthy tree, or transmitted through root grafts between trees growing within close proximity to one another. Because elms are most susceptible during the spring and early summer, when bark beetles are present, avoid pruning during this period to reduce the risk that the tree will contract the disease. Maintain good tree maintenance practices such as thoroughly watering during extended periods of drought, providing a 3- to 4-inch layer of compost and mulch around the base of trees, fertilizing, and periodic pruning to ensure your tree remains healthy and vigorous.

  • Generally speaking, plants get most of their water and nutrients from the top 12 inches of soil. The key is to keep roots moist, but don’t overdo it. Let the top few inches of soil dry out between waterings so that the roots and soil organisms can breathe.

    Newly planted trees and shrubs need thorough watering after initial planting and must be watered regularly until the roots have properly developed (two to three years). Concentrate on watering the root ball. Place a garden hose at the base of the plant and let it run slowly, soaking the soil to a depth of 2 to 3 inches. Watering too much or too little can result in injury to the plant.

    Established trees and shrubs will require supplemental watering if we have not received adequate rainfall. Trees and shrubs should receive at least 1 to 2 inches of water every seven to ten days throughout the growing season, more during an extremely dry period. Water plants slowly, deeply, and thoroughly under the canopy zone (from the trunk to the ends of the branches) rather than daily.

  • These sound like the symptoms of viburnum crown borer. Viburnum crown borer adults are clearwing moths that emerge from May to August and closely resemble wasps. They typically lay eggs in cracks on the stem about 12 inches above the ground. Small holes and the presence of a sawdust-like material are signs of a borer. When the eggs hatch, young larvae tunnel downward into the base of the plant, eventually killing the stem. Stressed plants are more susceptible to borer attack, so try to keep plants healthy by applying mulch around the base and watering well during dry periods. Chemical sprays are available and should be applied in June when wasps are active.

  • Your magnolia tree has magnolia scale. Scale insects are sucking insects that produce a sap that often causes leaves to turn black from sooty mold. Heavy infestations can cause twig dieback and kill branches. The adult scale continues to grow throughout the summer. They are covered with a white, mealy wax. The adult mother scale will give birth to young larvae, called crawlers, in late August to mid-September. The best time to kill the magnolia scale is when the young crawlers are present. There are a number of products available, including seasonal horticulture oils, insecticidal soaps, and chemical insecticides.

  • This may be the damage caused by viburnum leaf beetles. The larval stage of the beetle feed on new leaves for two to three weeks, causing numerous holes in the leaves. When mature, the larvae crawl to the ground, usually in mid-June, and pupate in the soil. Adults emerge from the soil (early July) and also chew on the leaves. Their feeding damage forms irregular round holes in the leaves. The beetles are about ¼-inch long and generally brown in color.

    The adult beetles will be mating and laying eggs from summer into fall. There is one generation of the beetle each year. Heavy and repeated defoliation by the viburnum leaf beetle can lead to death of the shrubs. Insecticides can be used on the larvae in May and June when they are feeding and on the adults in summer when they are feeding.

Fall

  • This seasonal needle loss, also called fall needle drop, is a natural occurrence triggered by weather and seasonal changes. Evergreens do not hold their needles forever; as they age, the needles will turn yellow, then brown, and then drop off. The change can be gradual or, with some species, quite rapid. It does not always occur every year. As long as needle drop is restricted to older growth and is not excessive, it is a normal and natural process.

  • You may want to wait until a bit later in the season to prune your trees. In early fall, the wounds caused by pruning close more slowly than at other times of year. For most trees, the best times for major pruning are in late fall (when plants are dormant) or in winter to early spring because wounds heal faster. Some plants, such as maple, elm, birch, and walnut are considered “bleeders” and should not be pruned in early spring when sap begins to rise. Wait on these trees until the leaves have emerged.

  • It depends on which type of hydrangea you have. Hydrangeas do not need to be pruned every year. Hydrangeas that flower on the old wood, such as oak-leaved hydrangea (Hydrangea quercifolia) and bigleaf hydrangea (H. macrophylla, such as Endless Summer® and Twist n Shout®), should be pruned right after flowering or during the summer. Annabelle (Hydrangea arborescens) and panicled hydrangeas (H. paniculata, such as Limelight) flower on new wood produced the same year, so they can be pruned in the late winter or early spring before they bloom. Avoid summer pruning or you will remove the new flower buds. Use the heading back technique to prune at the appropriate time of the year.

  • Clematis is divided into three basic categories to determine pruning times:

    • Group 1 (Type A) is typically a species of clematis (C. alpina and C. macropetala and their cultivars) that flowers in early spring. These vines produce their flower buds on the previous year’s stems. They can be pruned to keep them within their growing space, or to remove dead and unsightly foliage. They usually do not require pruning, but if needed, prune right after flowering is finished.
    • Group 2 (Type B) contains the large-flowered hybrids. This type normally blooms in the spring and possibly again in the fall. All of the clematis in Group 2 bloom on old wood (actually on short shoots from old wood) and should not be pruned except for removing deadwood in early spring after the leaf buds have begun to open slightly.
    • Group 3 (Type C) consists of the popular summer-blooming varieties, such as the C. viticellasC. jackmanii types; the herbaceous species, such as C. integrifolia and C. recta; and the late bloomers such as sweet autumn clematis (C. terniflora). They all produce flowers on new wood in the current year and should be pruned back in late winter to early spring to about 12 to 14 inches above the ground. Leave at least two pairs of buds, a total of four buds, on each stem of the plant to insure new growth.
  • All plants, especially conifers and broadleaf evergreens (e.g., boxwood and rhododendrons), are susceptible to winter desiccation from drying winds. Be sure plants have adequate soil moisture before the ground freezes. Shading plants from winter sun and airborne salt spray can also be helpful. Fasten burlap or plastic to stakes on the exposed side of plants. To prevent broken branches from heavy snow load, gently brush fresh snow from the branches before it freezes. Allow ice-encrusted branches to melt off naturally.

  • Cool-season grasses such as feather reed grass (Calamagrostis) can be divided from late winter to early spring or from late summer to early fall.  In the upper Midwest, spring division is the most reliable. Warm-season grasses such as fountain grass (Pennisetum) and silver grass (Miscanthus) should be divided when they are in active growth; late spring to early summer is the ideal time. Fall division of warm-season grasses is generally not recommended.

  • Those spots are a symptom of tar spot, a fungal leaf disease. It is primarily a cosmetic disease that will not kill the tree. Initial infection occurs in the spring and appears as small, yellowish spots. As the season progresses, the spots enlarge to roughly ¾ inch in diameter and the center becomes raised and turns black, resembling a glob of tar on the leaf surface. To reduce or eliminate tar spot, remove fallen leaves from the ground and discard them.

  • One of the best preventative measures to protect plants against animals is to construct a cylinder of hardware cloth, chicken wire, or fencing around plants to protect against the rabbits, mice, and deer that damage the bark and chew on twigs. Set up the fencing in the fall so stakes or support can go into the ground easily before the soil freezes. More persistent problems may require more vigorous management.

  • Spring flowering bulbs are planted in the fall, ideally in September and October, to allow them to establish roots before the top growth begins in the spring.  Planting too late may not give the bulb enough time to develop adequate roots. If it is November and the ground is not yet frozen, go ahead and plant your bulbs.  Water them well to settle the soil and then cover the soil with a thin layer of mulch or ground-up leaves to insulate the soil.  If you cannot dig holes, consider planting them in containers to force indoors later. The planted containers will require a 10- to 13-week cold period (an unheated garage works well) to trigger bulbs to grow roots and initiate flowers.

  • It depends on what type of oak you are trying to grow. Acorns from oaks in the white oak group (white, bur, swamp white) ripen in one year and will germinate as soon as they are planted in the fall. The oaks in the red oak group (red, pin, Hill’s) require two years to reach maturity before they will germinate.

  • The idea that oak leaves are too acidic to use as mulch is an old myth that you can happily ignore. Although oak leaves do contain tannins, the tannins are only slightly acidic and will not affect the growth of mulched plants.  In fact, leaves of all kinds can be a gardener’s best friend.  In nature, fallen leaves remain on the ground where they break down with the help of soil organisms, returning organic matter back to the soil. These nutrients act as a natural fertilizer for trees and shrubs. Decomposing leaves used as mulch also help to insulate the soil from extreme temperature fluctuations, increase the soil’s capacity to hold moisture, and eventually provide a more favorable root environment.

    It helps to mow or shred leaves before using them around your trees and shrubs or adding them to the compost bin.  This makes the leaves decompose faster and prevents the leaves from forming a tight mat that prevents water from interacting with the plants’ root systems. For best results, do not apply any more than 3 to 4 inches of leaf mulch.

Winter

  • As you search for that perfect holiday tree, careful selection for quality and freshness can keep the holidays safe and attractive. Needles should be firmly attached and pliable.  Pines retain their needles the longest, with Scots and red holding their needles longer than white pine.  Spruce trees drop their needles the fastest.

  • Rabbits can harm plants by eating small twigs and buds or clipping stems at a clean, 45 degree slant or knifelike cut.  Rabbits generally feed no more than two feet above the ground or at snow level. The best way to discourage and protect plants against rabbits is to enclose the plant in a cylinder of fencing. Chemical repellents will also discourage browsing but will need to be reapplied after a heavy rainfall.

  • If your juniper appears to be planted much too high, that could cause problems in the future. Erosion of the mound of soil could expose roots to the cold of winter and to drying air. Since it is frozen leave it alone, the soil and mulch provide some insulation for winter, then next spring when the ground has thawed, consider having the plants replanted to the correct depth.

  • If there actually is rot in the trunk it will continue to rot and get worse over time. Should the tree be hollow it could become a hazard and crack or break in the right circumstances.  It is not our recommendation to clean out cavities and wounds. Every situation is different. But when a wound has occurred the tree naturally develops a layer of cells that act as a barrier to compartmentalize the wound from the rest of the tree. You do not want to compromise this area. Have an arborist look at the tree and evaluate it for the best diagnosis.

  • The black growths on your tree are due to a fungus called black knot. This is a serious disease that affects plums and cherries (Prunus species). The conspicuous black gall does not appear until the second year of infection. As the knot grows it eventually cuts off the flow of water and nutrients to the branch, causing stunting, wilting, and dieback. Gradually the entire tree may weaken and die if the severity of the disease increases.

    Unfortunately it is very difficult to control. Pruning is the most important control measure. Research has shown pruning can reduce infection by 80%. Prune off all knots in late winter or early spring before growth starts. Bury, burn, or compost all discarded plant material. Pruning cuts should be made at least four to eight inches below any swellings or knots because the fungus grows beyond the edge of the knot. Pruning tools should be sterilized between cuts using 1 part bleach to 4 parts water.

  • Pruning is a process that not only removes wood, it encourages the growth of new wood. Try taking some of the stems down all the way to the ground. Then new growth will come from the base of the plant and will take a little longer to get tall. This will also open the plant to more light which will encourage development of more flowers on the remaining stems. If you still cut stems back half way, be sure to cut directly above a bud. Stubs occur when pruning cuts are not close enough to the next bud.

  • Winter can be a great time to prune while trees are dormant, but ultimately pruning depends on the age of the tree and goals for pruning. When trees are young, we are trying to develop a good form and strong structure and will likely be pruning yearly. After a tree has been in the landscape for a few years, hopefully the structure and form are set, and we turn to removal of problem branches and repair of damage, so pruning may not be needed every year. With older, mature trees it would be best to prune as needed. Basically that would involve looking at all the trees each year and only pruning the ones that have a need (storm damage, broken limbs, rot, disease, and crossing limbs). Talk to your arborist and see if he will give you an estimate on that type of plan. The Illinois Arborist Association has a website that lists companies with certified arborists (www.illinoisarborist.org).

  • When the temperature in winter is extremely cold, we expect to see some tip dieback (winter burn) and browning on evergreens, including broadleaf evergreens such as holly and rhododendrons. Winter burn occurs when evergreens naturally transpire but cannot replenish lost moisture because the ground is frozen.  Smaller plants fare better if there has been adequate snow cover to insulate them.

    Be patient and wait to see how well the new growth emerges before doing any severe pruning.  The new buds for this year’s growth on evergreens are in the tips of the branches; on holly they are hidden where there is a leaf attached. Surprisingly plants  can withstand extreme cold and will push out new growth once winter has lessened its grip. Most evergreens start to show growth sometime in early to mid-May.

  • Great question. Once a tree is past the stage of successful treatment, the question “Why keep it?” must be asked. If the tree is past treatment, it will be in decline and most likely die in a year or two. We have learned that ash trees contain  less water content than other trees, such as an oak, so when an ash tree is dead it becomes brittle with the possibility of becoming a hazard. The infested tree also contains a population of developing larvae. Removing that tree during the dormant season reduces the local population of emerald ash borers by destroying the tree at a time when those insects cannot spread to other trees. Reducing the population may not have a big impact in heavily infested areas, but could be useful in areas where the insect is less prevalent.

  • What you are describing sounds like a stem canker. There are no sprays to control cankers. Remove the infected stem to the ground in dry weather. Be sure to sterilize tools between cuts so the disease is not spread to a healthy stem.  Red twig dogwoods benefit from regular pruning. Pruning older stems promotes new growth, which has the brighter red color.

  • This winter injury is known as frost cracking. The bark of young trees can split open when temperatures drop quickly. It occurs most commonly on the south or west side of the tree where the sun warms the bark. The warmth expands the bark, then temperatures drop and the bark contracts more rapidly than the live wood below. A vertical split is the result. It becomes more obvious in the spring when the tree trunk starts to put on girth.  There is no treatment for bark splitting. The wound typically heals itself but can be vulnerable to disease as it heals. Keep the tree healthy by watering in dry periods. Wrapping is not recommended.

The Morton Arboretum is a leading source of science-based advice about trees, plants, and landscapes.

‘How-To’ Advice

Find expert advice on how to care for the trees and plants in your home or community garden or green spaces.

Solve a Problem

Learn about common tree and plant issues and how to deal with them in your home and community gardens.

Plant Selection

Get expert help selecting the right tree or plant for your planting site.

Tree and Plant Finder

Search tree and plant profiles for descriptions and details that can help you make knowledgeable choices to plan and maintain your home, garden, or community landscape.

Plant Records Database

You can search, browse, and learn more about the plants in The Morton Arboretum’s living collections by visiting the BRAHMS Online website and browse herbarium specimens from across the Chicago region in the vPlants website.

Selecting and Planting Trees Guide

This publication highlights key factors to consider when planting a tree, including planting site characteristics, purchasing a quality tree, planting a tree, and maintaining the newly planted tree.

Northern Illinois Tree Species List

Download and view this guide, which describes species that grow well in Northern Illinois and recommends best planting sites and best practices.

Plant Health Care Reports

Get the scoop on what’s in bloom, active pests and diseases, growing degree days, weather data, and more from the experts at the Arboretum’s Plant Clinic.

If you have used the Plant Clinic service and would like to provide some feedback, please follow the link below and fill out a short survey:

Plant Clinic Client Survey