By Judy Kunz
Stand on one of the many foothills surrounding Denver and one feature dominates the view: the beautiful canopy created by millions of trees growing throughout the city. Itap difficult to imagine this area without trees, and itap also hard to believe that there were almost no trees in the area prior to the arrival of settlers around 1858. With the exception of some native cottonwoods lining the creeks flowing eastward out of the foothills, no trees grew here naturally.
As prospectors and settlers in covered wagons, on horseback, and even traveling on foot flooded the Front Range in response to rumors of the discovery of gold, the population in the area exploded. While the Gold Rush was somewhat disappointing and short-lived, in the following years settlers continued to travel to the area, some bringing their own trees with them.
Because of the surrounding topography, the Denver basin lies in a semi-arid “rain shadow,” meaning that much of the moisture moving over the mountains falls at higher elevations, leaving little precipitation as the weather moves eastward over the city. Denver is high and dry.
But trees need water to survive. We all want the beauty of trees that cool the environment, add interest to the landscape, and provide refuge for local wildlife, including small mammals, birds and insects. With precipitation rates decreasing in recent years and water possibly becoming more scarce as demand outstrips supply, it makes sense to plant trees that can provide beauty and shade but require relatively less water.
Many trees currently growing in the metro area require a fair amount of water. Fortunately, there are cultivars (cultivated varieties) that can thrive here while requiring low to medium irrigation and can also adapt well to our alkaline soils. Here are the deciduous trees and conifers that perform well along the Front Range under sometimes difficult conditions for many other trees.
Deciduous trees
Kentucky Coffeetree (Gymnocladus dioicus): Podless cultivars are Espresso, Decaf, Skinny Latte and Prairie Titan. This tree has a low to medium water requirement. It prefers sun and can tolerate a wide range of soils, making it an excellent landscape tree. It has an interesting trunk texture and twig shape that is evident in winter. Early settlers used the seeds from native cultivars as a substitute for coffee beans. There are no pods to rake up in the fall with these varieties.
Elm (Ulmus davidiana David): Greenstone, Choicecity, Northern Express and New Horizon are cultivars that are resistant to elm leaf beetle and Dutch elm disease. At 50 feet tall, these varieties are smaller than the American elm, thrive in full to part sun, and require low to medium water.
Hawthorne (Crataegus viridis Green ‘Winter King’): This member of the rose family is outstanding as an ornamental tree. Spring blooms are white followed by orange fruit that can persist throughout the winter. The mature height is 20 to 30 feet tall and wide. It has a dense growth habit, and mass plantings can form an attractive hedge. It requires low to medium irrigation.
Honey locust (Gleditsia triacanthos): Thornless Common Imperial is a compact cultivar maturing at 30 feet tall. Shademaster has a vase-shaped habit and grows to 35 feet tall. Skyline is a large, thornless shade tree maturing at 45 feet. They require full to part sun and medium water. Imperial turns a rich golden orange in fall. Trunks of young trees should be wrapped in the winter.
Horse Chestnut (Aesculus hippocastanum): This common horse chestnut is native to Europe. It is salt-tolerant and requires medium irrigation. Itap a showy tree that attracts wildlife such as birds and squirrels, and it matures at 70 feet tall.
Linden (Tilia tomentosa Silver): Sterling Silver is up to 70 feet and 30 feet wide. Heart-shaped leaves with fruit clusters form in late summer. It tolerates sun and heat, has a low to medium water requirement, and is more resistant to the Japanese beetle.
Maple (Acer grandidentatum ‘Bigtooth’): This Colorado native requires low to medium water and matures at 35 feet tall. It is tolerant of diverse soil types and is a great choice for the Front Range area.
Maple (Acer tataricum ‘Hot Wings’): A smaller landscape tree, it matures at 15 to 18 feet tall with low to medium watering requirements. It does best in full sun to partial shade. Cream colored flowers in the spring are followed by brilliant red samaras that stand out in contrast to the green foliage.
Maple (Acer saccharum ‘Caddo’): Mature height is 30 to 50 feet. Native to Oklahoma, the leaves are deeply lobed, resistant to leaf scorch, and tolerant of high pH soils. This tree has a low to medium water requirement. Fall color ranges from yellow to orange.
Oak (Quercus muehlenbergii) Chinkapin: Mature height is 40 feet tall with low to medium water needs. Flowers in the spring are followed by acorns in the fall, and it is a favorite of urban wildlife.
Serviceberry (Amelanchier alnifolia) Saskatoon: A large multi-stemmed shrub or small tree reaching 18 feet in height, it produces clusters of white flowers in spring, followed by blue to purplish small, edible fruit that is high in essential minerals and can be eaten fresh or cooked. It is a favorite of local birds. Serviceberries have beautiful fall color.
Conifers
Commonly called evergreens, conifers can be a great addition to any landscape. They retain their needles throughout the winter, adding structure and a splash of color to an otherwise leafless view. During all winters, conifers need occasional watering when the ground is not frozen to maintain plant vigor and to keep their needles intact. Three conifers stand out as examples that thrive in Denver’s alkaline soils:
New Mexico Juniper (Juniperus monosperma): Native to the Southwest, this juniper is one of the most common cultivars. It grows to a maximum height of 40 feet and prefers dry conditions. It tolerates many types of soils, and its blue, fleshy cones are a food source for birds.
Rocky Mountain Juniper (Juniperus scopulorum): Popular varieties are ‘Welchii,’ ‘Gray Gleam,’ ‘Cologreen,’ ‘Wichita Blue’ and ‘Moonglow.’ They can reach 40 feet high and are drought-tolerant.
Pine (Pinus cembra) Swiss Stone Pine and (Pinus flexis) Vanderwolf’s Pyramid: Both have a low to medium water requirement and stand at 30 feet high.
As we move toward an uncertain precipitation future along the Front Range, trees and other plants that thrive here while demanding less water may be the best choice. Many of the trees listed can be found at local independent garden centers or can be ordered online.
Colorado State University offers a for the Front Range and their cultural requirements at planttalk.colostate.edu, and information on, at engagement.source.colostate.edu.
Judy Kunz is a freelance writer and a Colorado Master Gardener who lives in Arapahoe County.
