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Chicago Tribune
18-05-2025
- General
- Chicago Tribune
Look out for plants that may be problems
The plants in our yards and gardens bring us beauty and joy, but some of them also bring problems. 'A plant can be a problem in a number of different ways,' said Sharon Yiesla, plant knowledge specialist in the Plant Clinic at The Morton Arboretum in Lisle. Many problem plants, mainly trees and shrubs, are called out in the plant information pages of the Arboretum's website ( 'Before you plant anything, check it out to make sure you aren't bringing a danger or a high-maintenance headache to your yard,' she said. We're all familiar with weeds, which take root easily and spread more aggressively than we'd like, and may go places we don't want them or outcompete other plants that we prefer. Some weeds listed on the Arboretum's website are such a problem that they are officially designated in Illinois as 'exotic weeds' or 'noxious weeds.' Invasive plants are another major category. 'An invasive plant is more than just a plant that spreads easily,' Yiesla said. 'It's one that is not native to the area and whose presence negatively impacts, or is likely to impact, ecological, economic or human health.' In natural areas such as forest preserves, national parks, and the Arboretum's restored prairies and woodlands, invasive plants choke out native species and are a major threat to the native ecosystems. May is designated as Invasive Species Awareness Month to call attention to this problem. Exactly which plants are considered invasive varies from place to place, but the Midwest Invasive Plant Network ( and the Invasive Plant Atlas of the United States ( have detailed lists of invasive plants. The Arboretum lists some plants as 'potentially invasive,' meaning that in its own woods, prairies, tree collections and garden, the plant has been observed spreading too readily. 'They are plants we are keeping an eye on, and it may pay to be wary of them,' Yiesla said. Other trees and shrubs — including some that were once commonly planted in the Midwest — are not recommended by the Arboretum because they are too susceptible to extremely serious disease or insect problems. One familiar example is ash trees, which are prey to the emerald ash borer. Another is Austrian pine, which is susceptible to diplodia tip blight, Zimmerman pine moth and other afflictions. 'Austrian pines used to be widely planted, even overplanted,' she said. 'Over several decades, as more and more problems cropped up and more of the trees died, it became clear that they just don't work here.' A final category of problem plants is those that are dangerous because they cause skin irritations or are potentially toxic to handle or ingest. Poison ivy is a familiar example, but other dangerous plants include pokeweed, poison hemlock, giant hogweed and stinging nettle. The Arboretum's lists of problem plants and its recommendations are likely to shift over time, as more information becomes available and as new conditions emerge. 'Our weather will continue to change,' Yiesla said. 'That can lead to stress that makes many plants more susceptible to diseases and pests.' The problem plant information pages can help careful gardeners choose plants that are likely to be beautiful, healthy and easy to care for. 'Thorough research is your best defense to make sure you don't plant a problem,' she said.
Chicago Tribune
04-05-2025
- General
- Chicago Tribune
Choosing a tree? Not so fast.
'I want one that grows fast.' Often, that's the first criterion for homeowners shopping for a tree. But there's a catch. 'A fast-growing tree may require more maintenance and may not live as long,' said Sharon Yiesla, plant knowledge specialist in the Plant Clinic at The Morton Arboretum in Lisle. 'That makes it especially important to do your research and select just the right species or variety for what you want a tree to do.' Look at all the characteristics of the tree, not just how fast it grows. Weigh the pros and cons of the tree and see if it is right for your situation. Some trees that have a reputation for growing up quickly, such as silver maple and cottonwood, have weak wood or poor structure and are susceptible to breaking in storms, she said. Others, such as full-size varieties of arborvitae, may quickly outgrow the space or require frequent trimming. 'There are cultivated varieties of arborvitae that will stay smaller, but you need to choose carefully and not just buy what's readily available,' she said. Some trees with a relatively fast growth rate, such as tulip tree and disease-resistant hybrid varieties of elms, can live for decades without causing problems. Other good choices include the native sycamore, with its interesting bark and form; the native hackberry, a sturdy species that resists most diseases and pests; and the native hybrid Freeman's maple, with its stirring fall color. 'Investigate all aspects of the tree, not just the growth rate,' she said. 'Balance the pros and cons as you make a decision.' In some cases, such as a small tree that will only reach 20 feet, a tree that grows slowly may be preferable. Growth rates are relative. Even slow-growing trees are likely to add 8 to 12 inches a year, Yiesla said. A moderate growth rate usually means 12 to 18 inches a year, while fast-growing trees may add more than 2 feet annually. Before you choose a tree, take a step back and consider carefully what you want it to do. 'If it's for privacy, there may be a better way to make a screen, such as shrubs or even ornamental grasses,' she said. Taking the time to select the right kind of tree can save homeowners substantial expense and trouble in the long term. You can use the Arboretum's Search Trees and Plants tool to look for appropriate trees. It allows you to filter by many criteria, including growth rate. Or consult the Plant Clinic at by email, phone or in person. Pay careful attention to the mature size given for each species or cultivated variety. Remember that trees grow wider as they get taller, and be sure you have enough room. Site any tree well away from paths, driveways and buildings. Even a tree not known for growing fast will thrive better and grow more if you care for it properly. 'Give it plenty of space,' Yiesla said. Spread mulch in an even layer 3 inches deep in a wide ring around the tree, and keep that area weeded. Most importantly, water the tree well. When a tree is young, it doesn't have much of a root system to collect and store moisture, so it needs extra help to get enough water to fuel the growth of roots, branches and leaves. 'Check the soil around the tree often to see if it's moist,' she said. 'Water it deeply whenever the top inch or so of the soil feels dry.' It will be at least two or three years before a new tree can be expected to survive on rainfall. A well-chosen tree, well cared for, can add beauty, shade, privacy and many other amenities to a home landscape. 'Just take the time and trouble to choose wisely, to make sure you're investing in the right kind of tree,' Yiesla said.
Chicago Tribune
27-04-2025
- Health
- Chicago Tribune
Get to know your trees to keep them healthy
For a healthier landscape and a greener community, taking care of the trees you have is as important as planting new ones. 'We often think about planting trees around Arbor Day at the end of April, because we know more trees make the world better,' said Sharon Yiesla, plant knowledge specialist in the Plant Clinic at The Morton Arboretum in Lisle. 'But it's just as essential to make sure that the trees we've already got are in good health.' Large, mature trees are the ones that do good work for us, providing shade, capturing stormwater, handling air pollution, and making our communities more beautiful, safer and more restful. A tree you plant now will take decades to reach a really powerful size, so the trees that are already big are worth our attention, too. How can you tell whether a tree is in good health? 'Keep an eye on your trees all the time,' Yiesla said. 'Get to know what's normal for them, and watch for things that are different.' Then get expert help to figure out whether the difference is a problem. 'What's normal for one kind of tree may be abnormal for another kind,' she said. The critical question is whether this particular tree looks different from how it did in other years, when you know it was healthy. Some tree symptoms may be caused by diseases or pests; others may be caused by stress, such as compacted soil, drought or severe weather. 'Sometimes it's nothing. Sometimes something bad is happening,' Yiesla said. 'You won't know until you check it out.' Look at the tree's canopy of leaves and branches. Does it have fewer leaves than last year? Can you see bare branches at the top? Inspect individual leaves. Are they normal in size or too small? Are they the same color as usual, or are they too pale or yellowish? Do the veins stand out in a different color of green than the rest of the leaf, indicating that the tree is not producing enough chlorophyll? Are leaves eaten away, leaving only a skeleton of veins? Watch the blooms. If it is an ornamental tree with conspicuous flowers, such as a magnolia, redbud or horse-chestnut, does it flower the way it normally does? Or are there fewer flowers this season? Be alert for fall color. An early color change is a sign of stress. 'If you see fall color in July, there's a problem,' Yiesla said. Often in summer, the problem is drought stress, and it's an urgent call to water your trees in hot weather. Check out the bark. Are there patches of bark falling off? Are there big cracks, bare places or bulges? Are there places where the bark is discolored or feels damp on a dry day? Can you see sap flowing down the bark? Are there fungi growing on the trunk? They can indicate rot inside. Examine the branches. Look for wounds or places with cracked or peeling bark, especially if these occur in more than one place; they may be a sign of canker diseases. Also, look for swellings and growths around branches. 'These may be harmless insect galls, or they may indicate a serious fungus disease such as black knot,' she said. Hunt for eggs. Many insects lay their eggs in masses on the bark of trees. Fuzzy beige patches are likely to be spongy moth egg masses. Small light bumps may be spotted on lanternfly eggs. Get any suspected egg masses identified by an expert before you spray with pesticides or take any other action. To figure out what may be ailing your tree, take clear pictures and submit them to the Plant Clinic ( or other experts, such as university extension services. Take closeups of the top and bottom of damaged leaves, and also farther-away photos that show the overall shape and condition of the tree. The Plant Clinic can also help you identify a tree if you don't know what kind it is. 'Many diseases, pests and stresses only affect certain tree species, or they affect some kinds of trees differently,' Yiesla said. 'You'll be able to take better care of your tree if you know its name.'
Chicago Tribune
05-04-2025
- Climate
- Chicago Tribune
For cherry blossoms, choose carefully
Many small ornamental trees brighten the Chicago region with their spring blooms: redbuds, crabapples, serviceberries, magnolias, wild plums and many more. Cherries, not so much. The Japanese cherry trees (Prunus serrulata) that bloom in a cloud of pink in Tokyo and Washington, D.C., rarely thrive in this area, according to Sharon Yiesla, plant knowledge specialist in the Plant Clinic at The Morton Arboretum. One problem is the Chicago climate, which is more challenging than the milder conditions of Japan and the U.S. Southeast. 'Some cultivated varieties of Japanese cherries are said to be hardy in Zone 5, but the wild swings of weather we get in spring tend to be too much for them,' she said. 'They're also very susceptible to winter damage.' Japanese cherries are prone to disease, including a fungal infection called black knot. 'It's almost impossible to control,' Yiesla said. 'The only thing you can do is prune out the infected branches every winter.' Other pests and diseases that afflict Japanese cherries include powdery mildew, borers, mites and tent caterpillars. 'A Japanese cherry tree in the Chicago area is likely to be high-maintenance and short-lived,' she said. Another popular but troubled tree is Higan cherry (Prunus subhirtella), often sold in a weeping form. Like the Japanese flowering cherry, it is a short-lived tree that is susceptible to many insects and diseases when stressed. With so many other flowering trees to choose from, it's easy to find one that would be a better bet. For example, redbud (Cercis canadansis) is a native tree that is robust and lovely, with lavender-pink flowers that bloom along its dark branches. Several species of white-flowering serviceberry, including the Chicago-area native downy serviceberry (Amelanchier arborea), thrive in local landscapes. What if you have your heart absolutely set on a cherry? All hope is not lost. Sargent's cherry (Prunus sargentii) is more winter-hardy and adaptable than Japanese flowering cherry or Higan cherry. It grows in several places at the Arboretum, among the heart-lifting displays of crabapple trees and magnolias. Sargent's cherry has showy pink flowers in early spring and attractive, shiny brown bark. Like most trees with conspicuous spring flowers, it needs a full-sun site. 'It's not immune to all the ills of cherry trees, but Sargent's cherry does better here than most other species,' Yiesla said. The Plant Clinic ( can suggest other kinds of small spring-blooming trees that are well suited to this region. 'There's a flowering tree for every yard,' she said.
Chicago Tribune
15-03-2025
- Climate
- Chicago Tribune
Some crops need a cool start
Before too long, it will be time to start planting vegetables — at least some vegetables. 'Some crops, such as carrots, radishes and most leafy greens, actually prefer to grow in cooler soil before the heat of summer,' said Sharon Yiesla, plant knowledge specialist in the Plant Clinic at The Morton Arboretum in Lisle. Other vegetables, such as tomatoes, peppers and melons, need to wait at least until May, when the soil is thoroughly warm and any danger of frost is past. Cool-season crops can be started from seed indoors in early spring and the seedlings transplanted outdoors in April in the Chicago region, once the soil is thoroughly thawed and drained. 'You can start them from seed yourself or purchase transplants,' Yiesla said. 'You also can sow seeds of many cool-season vegetables directly into the garden soil, although it will take longer to get a crop.' Most cool-season vegetables sprout grow best in spring temperatures in the 50s, and the foliage can tolerate a night or two of freezing temperatures about 32 degrees, or even a sprinkling of snow. 'That's a good thing in the Chicago area, where our spring weather is extremely erratic,' she said. To hedge your bets against both cold spells and hot spells, space out each crop by sowing the seed or setting out transplants in batches over a period of two or three weeks. Make sure you choose a full-sun site for all vegetables, well away from any source of shade such as tree branches overhead. Cool-season vegetables include carrots, radishes, parsnips, turnips, beets, asparagus, peas, onions, garlic, kale, spinach, lettuce, potatoes, cabbage, cauliflower, Brussels sprouts and broccoli. 'Most leafy greens will turn bitter if they grow in hot weather,' she said. 'Time them so you can harvest before July when the real heat sets in.' Warm-season vegetables, on the other hand, thrive in the heat of summer and can't tolerate either having their seeds in cool spring soil or having their leaves nipped by cold weather. These crops include tomatoes, peppers, melons, beans, cucumbers, pumpkins and other hard-shelled squash, zucchini and summer squash, eggplant, sweet potatoes and sweet corn. Because the warm part of the Chicago-area growing season is so short, warm-season crops are usually started from seed indoors and grown for several weeks before they are transplanted outdoors. 'Plan your garden so you can plant them out in mid-May to early June,' Yiesla said. Some relatively cold-tolerant herbs such as parsley, cilantro, chervil, chives, dill and oregano, can be planted outdoors in mid-spring. Others, such as basil and thyme, are more tender and need warmer weather. 'Plant your basil when you plant your tomatoes,' she said. Not all varieties of any vegetable are the same. Some have been bred to be more tolerant of cold or heat, or will take more or less time to reach maturity. 'Read the seed packets or the catalog descriptions carefully,' Yiesla said. 'They will give you the specific information you need to plan when to plant each vegetable variety.' Planting times will usually be given in reference to the average expected date of the last frost. In most of the Chicago area, that is about May 15. 'That's just an average, though, and we have sometimes had frosts in late May,' she said. Play it safe by consulting the long-term weather forecast before you set out warm-season vegetables or other tender plants. Cool- and warm-season vegetables have different needs because they originally came from different climates. Kale, for example, comes from the Mediterranean region, where the winter is much like a cool Chicago spring. Tomatoes are native to Central America, which never sees a freeze. Potatoes come from the high, cool Andes mountains of Peru. 'Their genes tell plants when to sprout and grow,' Yiesla said. 'We need to plan our gardening around their basic natures.'
