Some Like It Hot! Tough Trees Defy Summer Heat And Drought

By Nancy Buley, Director of Communications, J. Frank Schmidt & Son Co.
Photographs courtesy of J. Frank Schmidt & Son Co.

Much of the Western United States suffered through a summer of unprecedented heat and drought. Shade trees certainly made the days more tolerable, and if you’re like me, you’re determined to plant trees and grow some shade before another summer rolls around.

Early autumn is prime time for tree planting. Although it may seem that spring is a more favorable time for planting, fall is a better time for establishing a healthy, vigorous, long-lived tree. Planted now, your tree will respond to the warm soil temperatures and will establish roots throughout the winter months in mild climates, or until the ground freezes in more severe climates. Roots will resume growing when the ground thaws. When spring arrives, your tree will be well established and will help deliver a cooler, shadier summer than many of us experienced this summer.

Now is also a great time of year to discover which shade trees are undaunted by heat, drought, high humidity, flooding or other weather extremes that came your way. It’s the perfect time to discover which trees breezed through a long, hot summer, and to select trees with outstanding fall color.

Now’s the time to visit garden centers, parks and public gardens and “test drive” shade cast by various trees. Do you want deep shade, dappled shade, a broad-spreading canopy, or a narrow, upright tree tailored to fit a tight space? Regardless of the size of your landscape, there’s a tree that’s right for you. If you observe, ask questions and buy a tree or trees based on thoughtful research, you’ll be rewarded by cool shade for many years to come.

Forest Green® Oak

Here in the Pacific Northwest, where the mercury soared to an unbelievable and unprecedented 110-plus degrees F., heat tolerance has been top of mind. In my own landscape, I’m thankful to have planted a pair of Forest Green® Oaks (Quercus frainetto ‘Schmidt’) 25 years ago. They now tower above my house and helped to keep it cool during those extraordinarily hot days. Selected from a Mediterranean species commonly known as Hungarian Oak, it is well-adapted to our hot, dry summers and cool, rainy winters.

Oaks, in general, are tolerant of heat and drought and are adaptable across a wide range of growing conditions. Other characteristics include deep roots, strong wood and open branch angles that contribute to storm resistant structures. There are many species, so it is important to consult with local experts to learn which is the best match for your landscape. Most species are too large for typical residential landscapes, but a number of narrow or columnar cultivars are a good fit and still cast substantial shade. Several are described below, including two that were star performers in a 17-year trial conducted by U.S. Forest Service urban foresters in California.

Chinkapin Oak (Quercus muehlenbergii) is a natural choice for dry and windswept locations. Its glossy dark green foliage casts refreshing shade throughout the summer and turns yellow to yellow brown in the fall. Sometimes called Yellow Chestnut Oak, this native of the Northeast and Midwest has a reputation for performing well in alkaline soils. Hardy through USDA Plant Hardiness Zone 5, it matures to a height and spread of about 45 feet after about 30 years in an average urban landscape setting.

Texas Red Oak (Quercus buckleyi) is a native of Texas and Oklahoma that offers bright fall color. Moderate in size for an oak, it grows in about 30 years to a height and spread of approximately 40’ x 40’. Green, glossy summer foliage turns orange red to red in autumn. Dr. Greg McPherson, retired USDA urban forester who lead the aforementioned 17-year performance trial, describes it in one of a series of videos about Climate Ready Trees presented by Tree Davis, a non-profit tree planting organization in Davis, California.

For those seeking shade in space-challenged settings, there are several oak cultivars tailor-made for landscapes that don’t have room for a classic, spreading oak. They offer the same oak adaptability and resilience in a slender package.

Crimson Spire® Oak

Crimson Spire® Oak (Quercus robur x) is a hybrid of our native White Oak (Quercus alba) and English Oak (Quercus robur). Introduced by our nursery more than 30 years ago, it is a tough and time-proven performer in landscapes from California to Colorado, Kansas to Chicago and beyond. Other narrow cultivars include Streetspire® Oak, Kindred Spirit® Oak, Regal Prince® Oak and Beacon® Oak (Quercus bicolor ‘Bonnie and Mike’). The last is a selection of Swamp White Oak (Quercus bicolor) which is well-known for heat and drought tolerance.

Beacon® Oak

For small-scale landscapes or container culture, we look to recommendations from Kansas, a state that’s known for extremes in heat and cold. Dr. Jason Griffin, plant breeder and director of the John Pair Horticultural Center located near Wichita, describes trees that sailed through the state’s historic heat and drought years of 2011-2012, in a nursery trade magazine article entitled “The League of Extraordinary Trees.” Two of the 10 tough and adaptable species he describes as having “superpowers” are small stature trees suitable for containers, courtyards and other small spaces:

Seven-Son Flower

Seven-Son Flower (Heptacodium miconioides) earned high praise from Dr. Griffin, who called it the “crape myrtle of the North.” It has a lush, tropical appearance in summer, with glossy green leaves that fall in autumn to reveal rugged branches with exfoliating, gray-brown bark. Fragrant while flowers appear in clusters of seven in late summer, inspiring the “Hepta-“ and “seven-son” segments of the Latin and common names. After the flower petals drop, the long-lasting ornamental calyxes remain on the plant. Bright red in color well into autumn, they are easily mistaken to be the flowers of crape myrtle. Left on its own, it will tend to grow as a large, rangy shrub, but it can easily be trained to be a single- or multi-stem tree.

Chinese Fringe Tree

Chinese Fringe Tree (Chionanthus retusus) delivers four-season beauty as well as heat and drought tolerance. Upright branches are smothered in clouds of fragrant white flowers in spring. A pollinator magnet when in bloom, it sports deep green, pest and disease-resistant summer foliage that turns yellow in autumn.

Tokyo Tower Chinese Fringe Tree (Chionanthus retusus ‘Tokyo Tower’) is an upright, narrow cultivar with predictable form (20’ height x 10’ spread) that bears small, blue-black fruits in autumn and delivers winter interest via golden-tan exfoliating bark.

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