By Julie Christensen
When you think of poplar trees, you probably think of the Lombardy poplar. This tree, with its fast growth and upright, columnar form, is frequently used as a windbreak or to line driveways and avenues. But, the poplar family includes more than 35 native species, such as cottonwoods, aspens and balsams.
These trees make fine landscaping trees because they grow quickly and most have brilliant yellow fall foliage. Cottonwoods make excellent shade trees and offer habitat for wildlife, while aspens work well in compact spaces. Balsam poplars are an ideal choice for moist soils. Poplars have some limitations, though, including weak wood and a propensity for disease.
Cottonwoods (Populus deltoids) grow throughout much of the U.S., and especially along streams and rivers. These large trees have a gnarled open form, rough bark and large, tear-shaped leaves that turn yellow in the fall. Female trees shed white fluff in the spring, hence the name.
Aspens (Populus tremuloides) grow at high altitude in the Rocky Mountains and a few other areas in the U.S. They have white bark, a straight trunk and tear-shaped leaves that “quake” in the wind, which is why they are sometimes called “quaking aspens.”
Balsam poplars (Populus balsamifera ssp) thrive in moist, swampy soil throughout the northern regions of North America. These trees reach 80 feet tall, with a tall, columnar trunk, rough bark and an open crown.
Lombardy poplars (Populus nigra ‘Italica’) were planted extensively on Victorian estates, but they’ve fallen out of favor in recent years because of their short lives and invasive roots. These trees have an upright form and brilliant fall foliage.
For close-up photos of the leaves and barks of the species above, check out these tree fact sheets from Virginia Tech University.
Note that Tulip Poplars (Liriodendron tulipifera), also called yellow poplars, are not actually part of the poplar family at all. They are known for their extremely tall growth and beautiful tulip-like yellow blossoms in the spring.
Poplar Tree Care
Poplars belong to the willow family and have similar care requirements. In warm, moist conditions, poplar trees grow as much as 24 inches in a year, making them one of the fastest-growing trees around. Unfortunately, many poplar trees are short-lived. Aspens and Lombardy poplars, in particular, rarely live more than 20 years.
Poplars grow best in full sun and moderately moist soil. These trees all have shallow roots and can cause damage to underground pipes and sidewalks. Cottonwoods and Lombardy poplars, in particular, have roots that extend into the surface of the soil, which makes mowing a lawn difficult and can cause a hazard in the yard. To control these problems, plant poplar trees at least 30 to 40 feet from your house, sidewalks and underground pipes. Mulch the area underneath the trees.
Poplars tolerate a variety of soil types, although aspens prefer slightly acidic soil. When planting any poplar tree, add compost or moistened peat moss to improve drainage. On heavy clay soils, consider using a raised bed. Unless you have very poor soil, you probably won’t need to fertilize established trees, especially if they’re growing near a fertilized lawn. In fact, too much fertilizer can encourage soft growth and disease and pests.
Poplar trees are notorious for producing suckers in the yard. These trees spread by seed, but they also reproduce through underground roots and suckers that eventually become new trees. A grove of aspens, for example, appears to be many trees, but the trees are actually one organism, sharing an underground root system. To control suckers, simply snip them back several times throughout the growing season or mow them down. When an older tree begins to die, cut it down and allow new suckers to take its place. Do not use systemic herbicides to kill suckers because the herbicide will spread through the root system and kill desirable trees as well.
Pests and Diseases of Poplar Trees
The main reason most poplars die young is their susceptibility to insect and disease problems. Aphids and oyster scale attack the leaves and stems, while borers tunnel through the trunk. To treat aphids and oyster scale, spray trees in spring with insecticidal oil, coating the leaves as well. To treat borers, prune out infected areas, which are evidenced by boring holes at the base of a branch, as well as leaf and tip dieback.
Poplar trees are susceptible to cankers and leaf spot diseases, as well. Fungicides are available to treat these diseases, but the most common response is simply to clean up leaf litter in the fall and prune out infected branches.
For more information, visit the following sites:
Lombardy Poplar from the University of Florida IFAS Extension
Cottonwood from the Great Plains Nature Center
Aspen Trees from Colorado State University Extension
Planting Poplars (video) from Utah State University Extension
When she’s not writing about gardening, food and canning, Julie Christensen enjoys spending time in her gardens, which includes perennials, vegetables and fruit trees. She’s written hundreds of gardening articles for the Gardening Channel, Garden Guides and San Francisco Gate, as well as several e-books.