Our view of the diversity and uniqueness of the existing plant collection at the Arboretum begins with the pre-settlement bur oak grove. It has been estimated that the largest bur oak trees are over 300 years old. The bur oak grove covers 12 acres on the hilly eastern fringe of the site. Tropical looking umbrella magnolias thrive beneath the oaks and display their 8” flowers atop 2’ long leaves. Impressive native trees among the grove include an enormous basswood, giant black cherries, white oak, shagbark hickory, black walnut and hackberry – contributors to Rockford’s beginnings as a furniture manufacturing center.
Over fifty species and cultivars of coniferous evergreens on site represent 9 groups from North America, Europe and Asia. Firs, Chamaecyparis, junipers, spruces, pines, Douglas fir, yews, arborvitae, and hemlock flourish with several stately plants of most species. The best of the lot include lush Nikko firs, contorted Meyer’s spruce, spiny Irish juniper, columnar spires arborvitae, and the shaggy threadleaf false cypress (Chamaecyparis pisifera ‘Filifera’). Most of the evergreens are forty or more years old.
Many plants thrive here near their northernmost outpost. Brilliant scarlet flowering red buckeyes, clumsy-looking devil’s walking-stick, snow white flowering dogwoods, dainty flowered Enkianthus, sourwood, Carolina silverbells, Japanese pagoda tree, sweetgum, Linden viburnum, wisteria, and emerald Moraine ashes enhance the site’s outstanding diversity. Plantsmen consider the flowering dogwood and sourwood two of Eastern North America’s most beautiful native plants. Klehm dogwoods flower and fruit reliably and the half dozen plus sourwoods reward us with their white lily-of-the-valley-like flowers and flaming red fall color.
Several plants found on the site are quite rare in cultivation. The spiny Hemiptelea from Northern China was a small tree unknown to all but Dr. Ware from Morton Arboretum. Fontanseia, a willow-like plant of the olive family, is another oddity. Three 30’ Meyer’s spruces have not made the pages of Hortus Third, the hefty reference we use to standardize plant names found on site. American chestnuts survive in the arboretum, despite having been decimated from their native range by the imported chestnut blight. Almost overlooked was an interesting groundcover from the Appalachian Mountains called shrub yellowroot that displays its dainty celery like leaves in two area of the Arboretum.
Klehm’s trees and shrubs represent all major floristic regions of the Northern Hemisphere. The arboretum’s exotic forests are reminiscent of Europe, Eastern and Central Asia, as well as Eastern and Western North America. Our European component includes mature Norway and English hedge maples, English oaks, English elm, European beeches, Horse chestnut, Austrian mugo and Scotch pines, as well as European species of larch, horn-beam, spindletree, and mountain ash. Corktrees, false cypress, katsuratree, Amur maple, Japanese red and white magnolias, flowering- quince, and various honeysuckles represent Eastern Asia. Forest giants of Eastern Northern America include American beech, yellow buckeye, cucumber tree and tulip tree. Western North America’s splendid conifers Ponderosa pine, Colorado blue spruce, Douglas firs, and succulent concolor firs complete the list.
Other specialties include our magnificent collection of six species of birch: Mature paper birches, various European white birches, New England’s gray birch, flaky barked river birches, coppery barked yellow birch, and the cherry-like sweet birch. The latter two species contain fragrant oil of wintergreen in their buds, twigs and bark. The fragrant shaggy white flowering fringetree, a small tree of the southeast United States and favorite of Thomas Jefferson at his Monticello estate, is so floriferous and fruitful that literally hundreds of naturalized plants occur throughout the arboretum. The tree collection also contains uncommon trees native to central and southern Illinois such as Shummard and scarlet oaks, Ohio buckeye, redbud, shellbark and mockernut hickory, and shrubby St. Johnswort. All in all, the collection of plants growing at the Klehm Arboretum comprises a living museum to educate the public on the earth’s rich assortment of plants.