Latest news with #SpencerCampbell
Chicago Tribune
11-05-2025
- General
- Chicago Tribune
After bloom, give shrubs a trim
Make plans now to prune spring-flowering shrubs, such as forsythia, lilac, viburnum and flowering quince, after they finish blooming. 'We don't prune these shrubs in winter because we'd be cutting off the buds that will open into spring flowers,' said Spencer Campbell, Plant Clinic manager at The Morton Arboretum in Lisle. 'Instead, we wait until after we've enjoyed their bloom, and then we prune them if they need it.' Timing is important. Ideally, you will prune these shrubs after they have bloomed but before they start forming the buds that will become next spring's flowers. 'There's a window of six or eight weeks,' he said. Prune flowering shrubs selectively, using hand pruners to remove only those stems or branches that need to go while leaving most branches to keep the shrub's natural form. 'Don't shear flowering shrubs into smooth shapes with a hedge trimmer,' Campbell said. 'It looks unnatural, and it will tend to reduce their bloom.' Think about your reasons for pruning before you start the job. 'Look the shrub over each year and assess what needs to be done,' he said. 'You don't always need to do much.' Be careful not to remove more than one-third of the stems in a shrub in any year, so the plant will always have enough leaves to support itself. Different species will require different pruning treatments. For advice on how to prune shrubs by species, go to Some possible reasons to prune are to remove dead or diseased wood; to keep an attractive, balanced form; to control the size of a shrub; to eliminate competition or collisions between branches; and to prevent the plants from becoming overgrown. For example, a forsythia is most attractive when it has an upright shape. However, it's a vigorous plant that easily becomes an unruly tangle. To tame it, keep those stems that have the most graceful, upright and arching form. Cut the more disorderly ones within an inch or two of the ground. Lilacs, too, can easily become overgrown. To keep a lilac shrub under control, 'take out two or three of the thickest, oldest stems each year,' Campbell said. Those older stems will be replaced by newer stems that usually bloom more. In general, follow some simple steps for routine pruning. First, cut out dead wood — dried-out, brittle branches that have no leaves. Remove branches that are broken or injured. Then look for branches that are crossing or rubbing against each other. To end the conflict, choose one branch to keep and remove the other. Prune out branches that make the shrub look awkward or that cause any obstruction, such as sticking out into a sidewalk or blocking a window. To reduce a shrub's overall size, remove the longest branches at their bases and cut other branches back to where they join a main stem. Remove any unwanted suckers that have sprouted from the shrub's root system. This guidance will work not only for spring-flowering shrubs but also for those that bloom in summer, such as rose of Sharon, summersweet or panicle hydrangeas. You will have more choices about timing with most summer-blooming shrubs, since they usually form their flower buds in spring. 'You can prune them after they finish blooming or wait until winter when they're dormant,' Campbell said. It's not necessary to deadhead, or remove spent flower heads, from shrubs and flowering trees. 'The plant will discard those by itself in time,' he said. 'The only reason to prune them out would be to make the shrub look more tidy.'
Chicago Tribune
29-03-2025
- General
- Chicago Tribune
Pussy willow can grow in a sunny, moist site
In early spring, bits of fluff appear along the branches of some willow shrubs, silvery gray and as soft to the touch as a kitten's paw. They may seem furry, but these are actually the flower buds of pussy willow (Salix discolor). The hairs are insulation, protecting the flowers inside the buds against cold weather until they bloom in late March or early April. 'Pussy willow is a large shrub or small tree that can be part of a home landscape if you have a site with plenty of space, full sun and moist soil,' said Spencer Campbell, Plant Clinic manager at The Morton Arboretum in Lisle. 'Children love it.' Pussy willows can be seen in the Children's Garden and the Willow Collection at the Arboretum. By early April, the bunches of silvery hairs, called catkins, will become tiny yellow flowers. Rich in pollen and nectar, these blooms are an early-season feast for many kinds of pollinating insects, including several kinds of native bees. The shrubs also host the larvae of 18 kinds of butterflies and moths, including eastern tiger swallowtail and mourning cloak butterflies. If you'd like to try growing pussy willow in your yard, check the tag to make sure you have chosen the native plant, Salix discolor. Several other non-native willow species have similar buds and are sometimes called pussy willow, but they don't provide the same support for native insects, and some of them are invasive. Most importantly, be sure to get a male plant. 'There are male and female plants, and only male pussy willows develop the pretty, silvery catkins,' Campbell said. Be aware that pussy willow has some requirements. 'It's not a small shrub,' Campbell said. 'It can grow to 25 feet tall and wide.' When it's not blooming, a pussy willow is unspectacular, but it is big enough to be a good privacy screen. The size can be controlled somewhat by pruning. Regular pruning in winter to open up the plant and remove the oldest stems will also result in larger catkins. A full-sun site with at least six hours of direct sunlight daily is essential. 'The branches need lots of sunlight to develop catkins,' Campbell said. Avoid planting a pussy willow near sewer pipes, since its fast-growing roots will seek out moisture. Pussy willow is a wetland plant and cannot tolerate drought. 'The good news is that it doesn't need well-drained soil, as long as there is plenty of organic matter,' he said. It might be a good choice for a low spot that always seems to be wet, or as the anchor and focal point of a rain garden. When you prune a pussy willow in winter, you can enjoy the branches and buds indoors. Make a fresh cut at the base of each stem and immediately place it in water. Keep the branches in a cool place for a few weeks. When the buds open to show the silvery fur, you can preserve them at that stage by removing the branches from water so they dry out and do not go on to bloom. Like many fast-growing trees and shrubs, pussy willows are relatively short-lived. 'The willow is likely to live 20 to 25 years, long enough for the children to enjoy it,' Campbell said. 'And in that time, it will feed a lot of bees and butterflies.'
Chicago Tribune
09-02-2025
- Climate
- Chicago Tribune
Know your numbers to tell if plants are hardy
When you're considering whether to add a plant to your garden this season, a crucial piece of information is its hardiness zone, usually given in a phrase like 'Zone 5' or 'Zones 4-7.' But what, exactly, does that mean? The numbers refer to the U.S. Department of Agriculture's Plant Hardiness Zone Map, which divides the country into geographic zones that have similar average winter temperatures. Higher zone numbers refer to warmer areas; lower-numbered zones are colder. 'The zone number given for a plant tells you the coldest zone in which it's likely to survive the average winter,' said Spencer Campbell, Plant Clinic manager at The Morton Arboretum in Lisle. Because plants have evolved in a wide range of places and climates, some species can withstand winter temperatures that others can't. For example, Eastern white pine trees, big bluestem grass and hostas can survive cold temperatures that would kill palm trees, canna lilies and impatiens. 'Those tolerances are called hardiness, and they're used to assign plants to the hardiness zones,' Campbell said. Most of the city of Chicago is in Zone 6. Much of the suburban area is in the slightly colder Zone 5. To find out your garden's hardiness zone, search by ZIP code on the USDA map at If a plant label or catalog description lists only one zone, such as Zone 3, that is the coldest zone in which the plant is winter-hardy. The plant also will be hardy in warmer zones with higher numbers. For example, a plant labeled for Zone 3 (northern Minnesota west to northern Montana) will surely be able to survive winters in Chicago's Zone 6. Each zone is divided into two subzones, A (colder) and B (not quite as cold). For example, the extreme northwestern corner of Illinois, including Galena, is in Zone 5A, while the rest of northern Illinois, including much of Chicago's suburbs, is in the slightly less cold Zone 5B. Nearly all of Chicago is in Zone 6A, but a narrow sliver along Lake Michigan is in the marginally warmer Zone 6B. When you're shopping for trees, shrubs or perennials, the hardiness zone should be one of the first things you check. 'There's no point in dwelling on plants that don't have a chance of making it through your winter,' Campbell said. At the same time, bear in mind that the system of hardiness zones has limitations. A zone number is not a guarantee. 'Many factors affect plants in winter,' Campbell said. 'If a Zone 5 plant dies in Wheaton, it may have been killed by an especially cold night, or stressed by drought or compacted soil or a pest or disease, or transplanted too late in the season. Or there may be a combination of factors that weakened the plant so it couldn't survive the cold.' Summer is a different matter. Hardiness zone numbers are only about winter cold. They say nothing about how plants will handle heat, drought, humidity, or any other climate condition. If a label says Zones 9-11 (Florida), all it tells you is that the plant will be killed by temperatures below freezing. There are no zone police. No standardized system or central authority assigns plants to hardiness zones. Very few plants have gone through rigorous scientific testing for hardiness. For most ornamental plants, the zone classification of each plant represents a general consensus based on decades of growing experience. For native plants, the zones may be based on where each plant is found in nature. In the case of a newly introduced cultivated variety, or cultivar, the plant breeder is responsible for putting the plant through years of trials and assigning it to a zone. 'Sometimes it turns out that a plant's assigned zone doesn't work in practice,' Campbell said. 'Plants are adaptable, but they don't always perform the same way in gardens as in field trials.' The zones are based on averages. 'Averages mask extremes,' he said. 'Each of these areas can have cold spells that are much colder than the average, and those extremes can kill plants.' The current USDA hardiness map is based on average low winter temperatures in the years 1991-2020. The climate is changing. Because average winter temperatures have been rising in recent decades, the zone map was revised in 1990, 2012 and 2023, shifting most places in the United States into slightly warmer hardiness zones. But plant-killing cold spells still happen even in the new warmer zones. 'The critical thing to remember is that the climate is also becoming more variable and unpredictable,' Campbell said. Sudden weather shifts have become more frequent, and winter freeze-and-thaw cycles can damage plants as much as bitter cold. Given the uncertainties, the smart move for a gardener is to play it safe. 'Choose plants that are rated for your zone or a colder one,' Campbell said. 'Care for your plants properly all season so they are healthy and well prepared for winter, and make sure to protect their roots with mulch.'
