Some Like It Hot and Dry
A good shade tree offers relief from the heat, but there are several fine selections that also stand up to drought.
There's no denying it: The past few summers have been brutally hot and brutally dry. With records shattering all over the country - and with the prediction that drought will persist, if not intensify - your customers and clients will be asking about shade. You can help them prepare for a warm future by recommending any of a number of shade trees that have proved themselves capable of handing the elements with grace.
Up to the challenge
Native and adapted trees that have withstood the test of time may be prime candidates for a hot and dry future, but J. Frank Schmidt & Son Co. in Boring, Ore., is taking things a step further. "Our breeding and selection program, led by Keith Warren, director of new product development, identifies superior selections of North American natives and exceptional trees from around the world," says Nancy Buley, Schmidt's director of communications. "There's great demand for native trees these days, but seedlings of native species have great variability and they often don't perform well in urban growing conditions.
"A major demand that we see in the future is the need for heat- and drought-tolerant trees that can handle the tough growing conditions of our cities," she continues. "Not only is the climate warming, but cities themselves create their own heat island effect that challenges even the toughest trees."
The company is always on the lookout for trees that have evolved in extreme climates - hotter, drier, colder, wetter. For example, the Carpinus betulus cultivar Emerald Avenue® is derived from a hot, dry, Mediterranean climate, and it is proving to be a tougher, more successful city tree.
"When selecting cultivars of native trees," Buley explains, "provenance of seed source is an important consideration. In answer to increased demand for low maintenance, drought and heat-tolerant trees, we seek out seed sources in areas where those growing conditions occur and trees have evolved to thrive in those conditions."
Schmidt's Oregon Trail® maple (Acer saccharum 'Hiawatha 1') is selected from an outstanding sugar maple that grows in the city of Hiawatha, Kan. Flashfire® maple ('JFS-Caddo') was selected as the outstanding sugar maple grown from seed collected in the Caddo Mountains of western Oklahoma.
Let's take a look at some specimens to spec now for future relief from drought and heat.
Emerald Avenue® hornbeam
Photos courtesy of J. Frank Schmidt & Son Co.
Emerald Avenue® hornbeam
Thanks to its superior heat and drought tolerance, adaptability to city conditions and upright, pyramidal growth habit, Carpinus betulus 'JFS-KW1CB' (PP 22,814) is an ideal street tree. It is grown from seed thought to have originated from the southernmost range of European hornbeam, which makes it similar in character but much more heat tolerant than other cultivars of the species, including the widely planted pyramidal European hornbeam. During the dog days of summer, when other cultivars of Carpinus betulus look tired and heat-stressed, Emerald Avenue maintains healthy, deep green foliage. Handsomely corrugated leaves are strongly textured, durable and pest- and disease-resistant. The foliage is buttery yellow in autumn.
Discovered by Keith Warren in the J. Frank Schmidt nursery, Emerald Avenue® was nicknamed "The Hulk" because of its strong trunk, dominant central leader and sturdy branch arrangement. Broadly pyramidal to oval in shape, it grows to approximately 40 feet in height and 28 feet in spread. The vigorous growth habit of this Zone 5 tree makes it easy and fast to grow. Minimal pruning and care are needed to develop a finished tree that is immediately sturdy and impressive in the landscape.
Crimson Sunset® maple
Crimson Sunset® maple
Crimson Sunset® maple (Acer truncatum × A. platanoides 'JFS-KW202'; PP 21838) flourishes in hot and humid climates where most purple-foliaged trees fail to thrive. Its deep purple leaves retain their dark, glossy color through the growing season, resisting the leaf tatter and scorch damage of late summer that typically disfigure other purple-leafed maples.
This medium size shade tree is perfectly shaped for street tree use, and compact enough for shading today's compact home landscapes. Although it is similar at first glance to the popular and widely planted Crimson King maple, its improved heat tolerance and leaf quality make it a natural choice for regions that are experiencing gradually warming temperatures. Upright and symmetrical branch habit and a strong central leader make it easy for growers to develop into a handsomely shaped shade tree.
Emerald Sunshine® elm
Emerald Sunshine® elm
The foliage of Ulmus propinqua 'JFS-Bieberich' - Emerald Sunshine elm - is strongly textured, emerging with red tints and maturing to deep, rich green. It is resistant to Dutch elm disease and phloem necrosis; plus, it resists the feeding of elm leaf beetles. This impressive elm was selected on the arid plains of western Oklahoma, making it a tough performer in urban settings. Mature height and spread are about 30 feet by 25 feet.
Crimson SpireT oak
Crimson Spire™ oak
Fast growing, cold hardy, drought-tolerant and disease resistant, Quercus robur × Q. alba 'Crimschmidt' (PP 9103) adapts to varied soils and tough urban growing conditions. Rich, dark green leaves stay fresh and bright through the heat of summer, turning rusty red to bright red in mid to late autumn. Pest-free and mildew resistant, this fast-growing compact shade tree is tailored for tight urban spaces. A proven performer on streets along Colorado's Front Range, it has also won thumbs up from customers in the hot, dry states of Utah, Kansas, Oklahoma and Missouri. In fact, Marcum's Nursery and Tree Farm in Stillwater, Okla., has named it among the company's "Drought 2011 Survivors." It's also an ideal choice for space-challenged residential landscapes where an easy-care tree is needed to cast cool shade while providing beauty and multi-season privacy screening.
Tailored for today's streetscapes and landscapes, Acer rubrum 'Frank Jr.' (PP 16769) is a heat-resistant, vigorous growing, colorful choice for sustainable landscapes. Its foliage is smaller and more refined that that of Acer × freemanii, with deep green, heat-resistant leaves that remain fresh looking all summer. Brilliant fall color appears early and is reliably bright red. Redpointe shows improved resistance to anthracnose, spider mites and leaf hoppers, and demonstrates superior resistance to leaf chlorosis.
A symmetrical, well-balanced form guided by a strong, straight, dominant central leader encourages well-behaved growth and eliminates the need for a lot of pruning and shaping to create a good, reliable canopy.
Shade trees are expected to provide a number of benefits, and heat- and drought-tolerance are becoming ever more important. Selecting the right tree for the right place - and preparing for challenging climate conditions ahead - will provide business benefits, as well.
Nancy Buley is communications director for J. Frank Schmidt & Son Co. in Boring, Ore., and an honorary member of the American Society of Landscape Architects. She can be reached at email@example.com. Sally Benson is editorial director for American Nurseryman. She can be reached at firstname.lastname@example.org.