Dr. Dirr

Dr. Michael Dirr's Latest Findings: Magnolia Virginiana- Sweetbay Magnolia

In previous tree profiles, I discussed Magnolia acuminata and M. × soulangeana and herein highlight an increasingly important landscape species, M. viginiana. It is becoming more common in contemporary landscapes because of new cultivars with smaller sizes, increased cold hardiness, and fully evergreen foliage into zone 6 landscapes. The impetus for this discussion resulted from […]

Dr. Dirr's Spotlight: Acer Pseudosieboldianum - Korean Maple

Certainly, easy to become monochromatic about small maples when Acer palmatum and the numerous cultivars are readily available via garden centers and mail order sources. Why look further? Well, if you live in the zone 3 to 5 regions of the U.S., then Japanese maple culture is challenging, if not impossible. Enter, Acer pseudosieboldianum, Korean […]

Dr. Dirr's Tree Spotlight: Quercus Lyrata-Overcup Oak

The overcup oak, Quercus lyrata, languished in landscape obscurity until the 1990s when several Georgia nurserymen realized and developed its potential. The University of Georgia campus is rich with Q. lyrata, no two alike, so the thinking went can the species be clonally/vegetatively propagated. Mike Glenn, Select Trees, Athens, and John Barbour, Bold Spring Nursery, […]

Dr. Dirr Tree Spotlight: Magnolia x soulangeana- saucer magnolia

The hope of spring is tethered to this species and the many cultivars. Difficult to imagine a garden, park, campus, golf course, city street, commercial property almost anywhere in the U.S. without a least one saucer magnolia. From Chicago to north Florida to the West Coast, the species can be successfully grown. The late Roger […]

Dr. Dirr's Tree Spotlight: Liriodendron tulipifera (Tuliptree)

From the arborists’ point of view, the tuliptree has more than its share of liabilities including excessively fast growth, limb breakage, drought-induced premature leaf abscission, and aphid/honeydew issues. Yet it is one of the most noble trees in the eastern North American deciduous forest. In Joyce Kilmer National Forest, the towering slender bole and narrow […]

Dr. Dirr's Tree Spotlight: Acer triflorum - Three-flower Maple

A beautiful maple, resoundingly/photogenically magnificent in shades of orange and red in autumn. Colors long persistent, from initiation to the crescendo, easily 3 to 4 weeks. Although Acer griseum receives the majority of garden accolades, this is the most adaptable, cold hardy, heat tolerant and reliable. In truth I love both, also certainly Acer maximowiczianum […]

Dr. Dirr Tree Spotlight: Thuja occidentalis-Eastern Arborvitae

Dr. Dirr's thoughts on the Eastern Arborvitae: Not quite sure why I never fully respected this soft-textured needle evergreen but an epiphany occurred during a seven-day circuitous, whirlwind-like, 2018 tour of Vermont. From Brattleboro to Burlington, in cultivation and the wild, the species was ubiquitous. Screening evergreens are few in this cold climate state, with […]

Styrax japonicus-Japanese snowbell

Beyond redbuds, Cercis, dogwoods, Cornus, flowering crabapples, Malus, and magnolias, Magnolia, there are precious few genera which offer significant cultivar diversity. Within eastern redbud, ~35 cultivars are known, varying in habit, foliage color, flower color, cold hardiness, and sterility. Dogwood, crabapple and magnolia cultivars number in the hundreds and continue to be introduced. So what […]

Dr. Dirr Tree Spotlight: Catalpa speciosa, northern or western catalpa, down but not out

Catalpa speciosa has never been commonly utilized in cultivated landscapes, yet somehow occurs in off-the-grid locations from Maine to Florida to the west coast. The species listed native range includes IN, IL, KY, TN, MO and AR. The USDA map it has naturalized in all but ~six western states. In Maine it appears with regularity, […]

Trees and College Campuses: A Mutual Symbiosis

A December, 2017 visit to Amherst, MA to enjoy a Georgia-University of Massachusetts (UMass) basketball game brought back fond memories of my graduate student days (Ph.D., 1972). UMass was founded in 1863 as the Massachusetts Agricultural College and is now a major research university with ~1,300 faculty and 29,000 students. It is the largest public […]

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