by Randall H. Miller

The Morton Arboretum is a world class, 1700-acre botanical garden of woody plants in Lisle, Illinois, 28 miles west of downtown Chicago. It is dedicated to collecting and studying woody plants from around the world, with the goal of learning how to grow them in ways that improve our environment.

Joy Morton (1855-1934), the proprietor of Morton Salt Company, founded the Arboretum in 1922 on his 735 acre Thornhill Estate. Joy was the eldest son of Julius Sterling Morton (1832-1902). Julius originated Arbor Day, and served as Secretary of Agriculture between 1893-1896 during President Grover Cleveland's second term. He established "Plant Trees" as the family motto, and Arbor Lodge, the family home in Nebraska City, Nebraska, is now a state park. In keeping with his family's motto, Joy was inspired to create a Midwestern Arboretum after visiting Harvard University's Arnold Arboretum.

In conceiving his Arboretum, Joy Morton sought the advice of the Arnold Arboretum's Dr. Charles Sprague Sargent. Sargent suggested Joy visit specific notable European Botanical Gardens, recommended landscape architects to design the facility, and encouraged the inclusion of an herbarium and library. Joy followed Sargent's advice, and hired Landscape Architect O.C. Simonds to create the original Arboretum design. This design was later expanded by Clarence Godshalk who served as the Arboretum's Director from 1937-1966. Joy appointed seven Morton family members, including his son Sterling and daughter Jean, along with two Morton Salt Executives to the Board of Trustees. Following Joy's death in 1934, Jean (Cudahy), served as Chairman of the Board until her death in 1953, when Sterling took over. Upon Sterling's death in 1961, his daughter Suzette (Davidson) acceded, and served as Chair until 1977 when she selected the current Chair, Charles Haffner III.

Now, the arboretum has expanded to 1700 acres and is home to 30,000 plants of 3,600 different types. It has extensive paths, and features an Administrative Building, the Thronhill Building (used for education), a Visitor's Center and a Research Center. Three hundred thousand people a year visit to study and enjoy the woody plants.

WOODY PLANT COLLECTIONS

Plants at the arboretum are grouped into geographic, taxonomic, and horticultural garden collections. Plants from around the world are evaluated for adaptability for use in the Chicago area's climate, and each plant is labeled with its name, location and date of acquisition.

Geographic Collections

There are 13 different geographic groupings, including Woody Plants of China, of Northern Illinois, of the Eastern United States, of the Ozarks, and the Appalachians. The China collection alone has over 770 plants representing 300 species, the Appalachian collection has 160 species, and the northern Illinois collection, while not started until 1981, already has over 120 plants.

Taxonomic Collections

The Arboretum has 21 Taxonomic Collections planted by family. Notable among them is the Elm family (Ulmaceae) collection. Started in 1926, it was one of the first taxonomic collections at the Arboretum, and with around 200 trees, it this is now one of the largest elm collections in the world. This collection has helped in the Arboretum's research locating trees resistant to Dutch Elm Disease and other common elm maladies. The Rose Family (Rosaceae) Collection is another major goup, with over 270 species including crabapples, mountain-ash, spireas, hawthorns, and roses. The pine family (Pinaceae) includes around 700 plants of 150 different types, and contains many outstanding specimens.

Horticultural Gardens and Collections

The horticultural gardens and collections are organized around either themes or plant types. An example of a theme collection is the Hedge Garden, a formal garden first planted in 1934, but renovated 60 years later. It features 30 sheared hedges, and 28 unsheared "natural" hedges of both deciduous and evergreen trees and shrubs. Other themes include the Fragrance Garden, Four Seasons Garden, and the May T. Watts Reading Garden. Adjacent to the Fragrance Garden are the Joy Path Gardens which feature bulbs and perennials setoff against a backdrop of flowering trees and shrubs. Examples of horticultural gardens centered on plant types include the Ground Cover Garden and Dwarf Woody Plants Garden. The Ground Cover Garden displays 500 different woody and herbaceous ground cover plants arranged for sun, partial shade and shade.

RESEARCH

Research has always been a priority at the Morton Arboretum. It has a practical orientation, probing for solutions to problems in cultivating trees and other plants in urban settings. Work concentrates around the Research Center that was opened in 1982, but extends to allied institutions or organizations. Research areas include the Herbarium, Urban Horticulture, Plant Pathology, Developing New Trees for Landscapes, Tree Roots in Urban Landscapes, Soils and Tree Growth, Natural Areas Ecology, and Rare Plant Conservation.

Herbarium

The Herbarium, with 165,000 specimens, is the third largest arboretum herbarium in North America. Dr. Charles Sprague Sargent seeded it in the early 1920's with donations. It includes specimens collected in the early 1900's by E.J. Palmer, 20,000 others from the Yellowstone National Park area by Erwin Evert, and representatives from the western panhandle of Florida and southern Alabama. Vouchers of plants for the National Cancer Institute's Anti-AIDS and Cancer Testing Program are also housed in the Herbarium.

Urban Horticulture

Urban Environments impose stresses on trees they often do not find in nature, and may not be adapted to withstand. The Urban Horticulture program at the Morton Arboretum is dedicated to expanding the diversity of plants suitable for urban environments. It has been developed to determine the horticultural, ecological and aesthetic values of trees and shrubs, and their suitability for wide use in urban landscapes. To assess plants for their commercial potential, and to develop new techniques for cultivating woody plants.

Plant Pathology

Plant pathology research at the Arboretum has several focuses: the susceptibility of various oak species to Armillaria root rot, and how long tree pathogens can persist in mulch and how to safely treat mulch if there is a problem. Finally, it examines how a plant growth regulator that stimulates root growth may impact tree diseases.

Developing New Trees for Landscapes

Plant collections at the Arboretum provide resource for a developing woody plants adapted to growing conditions in the Chicago area. The focus is not only on environmental adaptations, but also on ornamental character. An important part of this initiative is the Elm Breeding project. Elms have been under siege from Dutch Elm Disease, Elm Leaf Beetle, and Elm Yellows. The Elm Breeding project leverages the Arboretum's outstanding elm collection to develop cultivars resistant to these maladies.

Tree Roots in Urban Landscapes

One of the great contributions to arboriculture in recent years has been work originating at the Morton Arboretum on tree roots. Most trees have root systems that spread far beyond the tree crown, and are mostly located in the top 18" of the soil surface. Insufficient rooting space, poor soil drainage and compaction are conditions frequently found in urban areas that stress plants, and make them more susceptible to opportunistic insect and disease pests. Treatments derived from research at the Morton Arboretum attempts to improve tree health by recreating natural rooting conditions. Recommendations now include surface mulching, sold amendments, soil replacement, and elimination of competition.

Soils and Tree Growth

Research in the Morton Arboretum's soil Characterization Laboratory attempts to characterize urban soil, and develop soil in natural areas of Northern Illinois. It examines the effect of chemical contaminant on tree growth, and creating fill soils that are suitable for woody plant growth. Soil development research currently centers on wetland hydrology in northeastern Illinois. Work is underway to restore and develop riparian corridors in the Chicago area.

Natural Areas Ecology

The Morton Arboretum has emphasized natural ecosystems for 60 years. Recent work centers on habitat restoration, natural area management initiatives, and conservation of rare and endangered plants. Six hundred acres of the Arboretum are oak woodland. This vast area provides an outdoor laboratory to develop tactics to suppress invasive exotic plants. Research not only focuses on the plants, but on the system, including animals, fungi and soil.

Rare Plant Conservation

The Arboretum joined the Center for Plant Conservation of the Missouri Botanical Garden in 1996. The Center networks 28 arboreta and botanical gardens to maintain a National Collection of Endangered Plants. For its part in the project, the Morton Arboretum collects specimens or seeds of rare plants with the goal of re-introducing them into the wild. In particular, the Arboretum has developed a dolomite and gravel prairie for endangered species from that environment.

EDUCATIONAL PROGRAMS

The Arboretum also has a full schedule of Seminars, Workshops and Special Events for people ranging from the home gardener to the professional. They offer certificate programs for naturalists, home landscape horticulturists, and botanical artists. They have also recently hosted international symposia on elms, and the landscape below the ground.

CONCLUSION

The Morton Arboretum is another legacy of the Morton Family who have also given us Arbor Day. The Arboretum was managed and developed by Morton family members for 75 years. It now comprises 1700 acres, 30,000 plants, extensive plantings, a Research Center, a Visitor Center and an Education Center. It has Woody Plant Collections grouped on geographic, taxonomic and horticultural themes. It also features research focuses centered on Urban Horticulture, Plant Pathology, Developing New Trees for Landscapes, Tree Roots in Urban Landscapes, Soils and tree Growth, Natural Areas Ecology, Rare Plant Conservation and an Herbarium. The Arboretum also hosts an extensive schedule of seminars workshops and special events. Three hundred thousand people per year visit to study and enjoy one of the great arboreta of the world.

This article was compiled from information included in the Morton Arboretum home page, www.mortonarb.org.

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