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HOW TO USE THIS BOOK

MIDWESTERN GARDENING and landscaping take into account the changing seasons, so we present our book on woody species in sections entitled Spring, Summer, Fall, and Winter. Spring focuses on spring flowers. Summer looks at summer flowers and shade. Fall features leaf color. In winter, bark, decorative shapes, and evergreens become the focus. Each season is subdivided into shrubs and trees (species sometimes overlap) and contains a selection of alphabetically listed (in red) nonnative (introduced, alien, exotic) woody plants that are popular in the Midwest (each followed by one or more native species, listed in green). For maximum accessibility, we list the plants by their common names. Later references to the plant use only the first common name listed. Following a plant’s common name or names, we list its family, genus, and, in parentheses, species. When we repeat the genus name, it is abbreviated, as in this example: H. cinerea instead of Hydrangea cinerea. We provide the nonnative plant’s origin (not shown in USDA PLANTS), frequently Asia or Europe. Next we present the plant’s height, notable ornamental features (flowers, fruit, fall color), and cultivation requirements. We provide Ecological Threat notes, based on USDA PLANTS maps designating nonnative plants naturalized in the Midwest (eastern half of the United States). USDA PLANTS maps reveal the great extent to which nonnative woody and herbaceous species have moved into our midwestern ecosystems. Using “I” for “Introduced” and defining the term as “naturalized,” USDA PLANTS states, “In general, introduced plants are likely to invade or become noxious since they lack co-evolved competitors and natural enemies to control their populations.”¹ No single clear controlling entity defines the term invasive, or designates a species as being invasive or not. To determine if a nonnative plant is invasive, we relied on data from a variety of invasive plant organizations and governmental resources that evaluate plant species for invasiveness. For information on these resources, please see Selected Bibliography and Resources.

Following each nonnative plant entry is at least one midwestern native woody species (listed in green) that resembles the nonnative plant in height, notable ornamental features (flowers, fruit, fall color), and cultivation requirements. An entry in, say, Spring may mention summer fruit, fall color, or overwintering leaves or berries, so we cross-reference to identify native woody species that have multiple seasons of interest. The US National Arboretum defines a native plant as “one that occurs naturally in a particular region, ecosystem, or habitat without direct or indirect human intervention. We consider the flora present at the time Europeans arrived in North America as the species native to the eastern United States.”² “Even though their offspring reproduce and spread naturally (without human help), naturalized plants do not, over time, become native members of the local plant community.”³ We verified that a plant is native, “N,” through USDA PLANTS, and checked its subordinate taxa (varieties) and maps for distribution. A Nature Note following each native plant entry references some of the vital connections between the native plant and wildlife, especially butterflies, other native insects, and birds. Because most native insects (including butterflies) lay their eggs on native plants, and require them for successful reproduction, and most birds feed caterpillars (larval stage of Lepidoptera—butterflies/moths) and other insects to their offspring, we provide the number of Lepidoptera species hosted by many of the native woody species, based on Douglas Tallamy’s studies on butterfly and moth productivity. (Please see Selected Bibliography and Resources for Native Woody Species and Native Herbaceous Species in Descending Order of Lepidoptera Productivity.) We note when a plant has become rare, threatened, endangered, or extirpated in the region, according to information provided by USDA PLANTS. Our sources include the Morton Arboretum’s “Not recommended” species, and “Plants Tolerant to Black Walnut;”⁴ Christopher Starbuck’s “unusual trees” for specimen planting;⁵ and data from “Average and Maximum Lifespan of Virginia Trees.”⁶

Selecting popular nonnative shrubs and trees was an eye-opener. The choices offered by most mail order catalogs, big-box stores, generalist nurseries, and garden centers are between one nonnative and another nonnative plant. Nonnative plants commercially offered are often invasive species and their hybrids and cultivars. Because popular nonnative plant cultivars sold as “safe” to natural areas reduce—but do not eliminate—viable seeds, at this time all cultivars of nonnative invasive plants remain invasive.⁷

Evaluating popular native woody species was also revealing. “Nearly every plant currently available is a cultivar of a native.”⁸ To determine a plant’s true identity, read its label; its Latin name should be listed. If you have questions, have the proprietor provide a USDA PLANTS printout. Enter into a computer search screen the plant’s name(s) as shown on the label followed by USDA PLANTS. “I” for “introduced” is a nonnative plant that has naturalized. “N” is for “native.” Maps show the plant’s distribution. USDA PLANTS does not provide cultivar/nativar information. However, the plant’s label should. (See Introduction, p. 9). Have the seller verify that a native plant is not a cultivar/nativar.

Our focus on native plants in the Midwest, an admittedly broad and imprecise region, is complicated by the existence of varying definitions, categories, and climate zones. We include locations with similar native plant gardening conditions: Arkansas, Illinois, Indiana, Iowa, Kansas, Kentucky, Michigan, Minnesota, Missouri, Ohio, Wisconsin, and Ontario, Canada. Our suggestions for native shrubs and trees apply to most adjacent states and the states within the eastern broadleaf forest province (see below).

USDA Hardiness Zones Maps show ten different zones, each of which represents an area of winter hardiness for the plants in our landscape. This book provides information on each entry’s zones, but some are changing. For example, the U.S. Department of Agriculture puts Chicago into Plant Hardiness Zone 5b, with the outlying areas falling into the slightly colder Zone 5a. The Arbor Day Foundation’s updated hardiness map places the Chicago lakefront and southern suburbs into the upper reaches of Zone 6.⁹ For the most current guidance in choosing plants that do well in specific parts of the region, refer to the USDA Hardiness Zone map. Plants that share midwestern hardiness zones but are native to entirely different geographical locations and ecosystems are poor choices for midwestern landscapes. “Hardiness ratings alone are inadequate to guide landscapers in selecting the most successful plants,” states the US National Arboretum.¹⁰ Another way of analyzing the region to which a plant is native is by its plant province or regional vegetation type. Most midwestern states we reference fall within the eastern broadleaf forest province or vegetation type.¹¹

Many homeowners, gardeners, and landscapers seek to benefit the greatest number of Lepidoptera (butterflies/moths) and the birds that eat and feed the caterpillars to their offspring, by planting their host plants. To determine if a butterfly is local in your area, Jeffrey S. Pippen, of Duke University’s Nicholas School of the Environment, recommends accessing Butterflies and Moths of North America. (Please see Butterflies, Moths, and Other Insects in Selected Bibliography and Resources.) We show the number of caterpillar species produced by many of the native host plants. For a consolidated listing, please see Selected Bibliography and Resources for both Native Woody Species and Native Herbaceous Species in Descending Order of Lepidoptera Productivity.

Some plants in this book may be familiar under other names, both common and Latin. Because a plant’s botanical name is its only positive identification, its botanical name should be verified before making a purchase or before incorporating plants even when they have been provided by a neighbor or friend. Occasionally botanical names change, so if one doesn’t ring a bell, check its current status. This is also true of animal names, especially butterflies, whose common and scientific names have changed significantly, some quite recently, over the past century.

Shrub and tree heights, blooming and fruiting times, and cultivation requirements can vary with a plant’s geographical location and because of light and soil differences and other environmental factors. These variations can give rise to different information from different sources. For the best results, before you purchase a shrub or tree discuss its specific requirements with the purveyor or landscaper. We do not delve deeply into the many diseases and disorders that affect woody plants or the toxicity of various species to humans and animals. As one midwestern state extension agency points out, “Despite providing our trees and shrubs with all their necessities, diseases and insects can still cause problems. In most cases, however, healthy mature trees and shrubs are able to defend themselves against minor insect and fungal disease exposure without intervention by us.”¹² “If you can minimize environmental stress by choosing plants suitable for your light, soil, and temperature conditions, most of them should grow reasonably well, and if not, try them in another spot or get something else,” writes William Cullina, adding, “I firmly believe that there is no plant worth growing if it must be maintained by applications of poisons.”¹³ Hybrids and cultivars bred for disease resistance may be less susceptible to a particular disease but not to all diseases and problems. A study notes, “It is important to note that the term disease resistance does not mean that the plant is completely immune to disease but instead refers to a plant’s ability to minimize infection by the pathogen. Unfortunately, no cultivar is resistant to all diseases.”¹⁴ In fact, like the Irish potato, because cultivars and nativars are genetically deprived of a variety of the “tools” necessary to adapt to change, “They could be considered more vulnerable by virtue of their sameness,” writes Wild Ones.¹⁵

Native woody species play an indispensable aesthetic and environmental role in midwestern urban, suburban, and rural landscaping. We encourage consumers to patronize native plant nurseries and when hiring landscapers or visiting general nurseries, to insist that these establishments provide you only with true native species.