Used sparingly and placed right, small trees--particularly those that flower or offer coloration--can enhance any urban landscape. Intermediate or small ornamental trees that tolerate shade, or filtered light, can be planted beneath the canopies of larger trees for beauty and diversity. Many of these understory trees are low maintenance, requiring little pruning, and adapt well to a wide range of climatic conditions, soils, insects and diseases. They also perform well in areas where root zones are restricted.
Michael Tennant is a landscape architect and horticulturist who is director of Landscape Design/Installation Landscape for Chem-Turf/Russell Companies, Inc., in Norcross, Georgia.
Japanese maple (acer palmatum) is characterized
by palmate-type leaves. Several varieties, including
those with brilliant red foliage, make attractive
understory choices. Depending on the cultivar,
this species is 12-25 feet tall at maturity.
He describes understories as 'accent' trees. "If you can create a mental image, you have four or five Shumard oaks or pin oaks, five to seven inches in caliper; you use a dogwood understory of those trees, to bring your attention down to the middle; and then plant azaleas in front. It's a real attention grabber," explains Tennant. You see the mass of the hardwoods, but the understory trees enable you to soften the area. It also allows you to create your own little outdoor 'room' in an area. You can put a bench there."
Multi-trunk trees are becoming a popular landscape element, adding a welcome dimension to design and visual appeal. Several species, including redbud, dogwood, and maple, endure in the low light conditions of the understory. Redbud and dogwood are the most abundant of the shade-tolerant species. Unlike most flowering trees, which are adapted to full sunlight, these two species are shady character -- faring better where there is partial shade all day, especially in the afternoon.
The Eastern Redbud (cercis canadensis), which offers profuse, rosy pink flowers prior to leaf in early spring, reaches a maximum height of about 20 feet. Distinctive, heart-shaped leaves and an unusual, asymmetrical shape are other nice characteristics of this tree. Its foliage turns yellow in fall, followed by clusters of dark brown pods. Redbud does best in partial shade and will live about 25 years. Its lifespan is cut significantly if planted in full sun. Its cousin, the Texas Redbud (leguminosae cercis canadensis var. texensis), offers similar beauty, but is not quite as large and is more drought tolerant.
"Dogwood and Japanese maple are two key favorites, especially the Japanese Maple, because there are so many different varieties," says Tennant. "You can get different leaf textures, growth habits, and different tolerances of shade. The low-mounding type dissectum has an oriental look, in both its trunk and foliage. Watch out for leaf burn if it's planted near pavement. They do better in part shade, especially the lacy-leafed varieties. I also like smoke trees. They have good burgundy foliage, and their blue-gray blooms are phenomenal. It looks like a cloud of smoke when it's in full bloom."
Bloodgood is one of the most popular Japanese maples. It is an upright red-leafed type with black-red palmated leaves that retain their color extremely well. Brilliant red seed pods add visual interest in spring. When mature, it stands 15-18 feet, with a canopy of equal diameter. Acer palmatum dissectums, the small, cascading or weeping varieties of Japanese Maples, make an eye-catching addition to any landscape and are particularly lovely near ponds. Crimson Queen, top-seller of all the weeping lacy-leafed varieties, provides deep red color during the summer and dons deep scarlet attire in the autumn. As it matures, this Japanese maple variety develops a beautiful, cascading shape, ultimately reaching a height of about 9 feet. Viridis, another weeping variety, which has green lacy leaves that turn gold and crimson in the fall. It reaches a maximum height of 12 feet.
Japanese maples favor a moist, fertile soil, supplemented with a mulch of wood chips, shredded leaves, peat moss or leaf mold. When temperatures are above 90 degrees Fahrenheit, trees require about an inch of water per week. Over watering can cause root rot.
Of the dogwood varieties, Tennant says, "Kousa dogwoods are nice. There are several different types. The Milky Way has variegated colors of blooms, which is a nice effect. Dogwoods are average in price. Japanese maples are a little bit higher. They are in high demand right now. People are recognizing their beauty and performance and want them."
The Flowering Dogwoods (cornus florida) are small with very dense wood that average 20 feet in height and have flowers in the spring that are pink or white in color. They bear glossy, red, fruits and shiny, scarlet leaves in fall. Grown as an understory tree, the Rough Leaf Dogwood (coraceae cornus drummondii) is airy and delicate, with clusters of small white flowers in late spring and berries at summer's end. This dogwood, which seldom grows over 16 feet tall, requires alkaline soil and is drought-tolerant once established.
Yaupon holly used in an understory setting.
Slightly taller at maturity, the Japanese dogwood (cornus kousa) is rounded with horizontal branching and blooms later than flowering dogwoods, though similar in cultural requirements. This variety produces large, pointed, white-to-pinkish bracts and medium-sized, raspberry-like fruit that attract birds. Its leaves turn a burning red in fall.
The Cornelian cherry dogwood (cornus mas), a shrub-like variety, approaches 20 feet at maturity, and has distinctive clusters of small yellow flowers before foliage appears. Fall foliage is red. Birds love its cherry-type fruit.
Generally speaking, dogwood trees prefer rich, well-drained soil, but they have the amazing ability to flourish on poor growing sites. They are hardy and relatively pest-free. Dogwoods should be planted on the north or east side of a building, or beneath the shade of other trees.
Tennant, a graduate of Auburn University, is in the process of installing, as a community service, all the plant materials for the new Gwinnett County Chamber of Commerce building, headquarters for their local United Way. He offers the following method for planting understory trees:
"Dig a hole about twice the size of the rootball or container. Make sure once you set the plant -- once you scarify the side of the rootball -- that it has enough room to grow out, especially if it's root-bound. The roots must be able to venture out," he says. "Then, take posthole diggers, go straight down and dig a deeper hole in the center bottom. Put some kind of aggregate in it so when the water comes down, it drains. This is key. I always do it this way when I plant dogwood. Make sure you plant it one-half to three-fourths of an inch high. Don't plant it too low, especially a dogwood. Dogwoods are susceptible to wet feet."
With a little more planning and research at the front-end of a project, an interesting and complex landscape can be created with the use of understory trees.