Top 10 Trees
Kentucky tree experts provide their list of diverse tree recommendations for homeowners, with tips for choosing and planting so they will thrive
One of the botanical ideas most of us have learned in the last few decades is the idea of “invasiveness”—the non-native plants that, once introduced into an ecosystem, spread everywhere. Kudzu is the classic example.
Peter Barber, the partnership coordinator of the Kentucky Division of Forestry’s urban and community forestry program (www.forestry.ky.gov) shares his thoughts on the problem of ecological invasiveness. Tree of Heaven (also called stinking sumac) “can colonize our fields and woodlands,” Barber says. “Wherever they’re growing, a native tree is not growing.”
But trees that aren’t ecologically invasive can be harmful in a more subtle way, by a kind of invasiveness of the imagination—they reduce an ecosystem’s biodiversity by being used too widely.
Dena Rae Garvue, horticulture director at Bernheim Forest (www.bernheim.org), says, “Basically, maybe 20 to 25 trees are the most common for urban settings and you see them throughout” cities and towns.
Barber notes that while the pin oak is a fine tree, it’s been planted so widely (especially in cities) that there’s really not much point in planting another one. Kristopher Stone, director of the Boone County Arboretum in Union (www.bcarboretum.org) and blogger for Kentucky Gardener magazine, nominates the red maple as another overplanted species. “Not that we shouldn’t plant them, but you always want to have a way to avoid monoculture,” he says.
So let’s get more diverse. This article, based on recommendations from several Kentucky tree experts, suggests some trees that homeowners might like to plant. They’ve been chosen to bring some new, or at any rate less common, varieties to your attention. A good number are native trees; all of them are suited to Kentucky’s climate, are pest-resistant, and not invasive.
But don’t just take our list and head for the nursery. You’ve got a lot of work to do first.
The cliché in horticulture is “the right tree in the right place.” But that simple formulation involves a lot of thinking.
The most important factor is to look into the future—to know how your tree is going to grow. “People purchase plants when they’re in a small container and they go, ‘Oh, I like this. It has beautiful architecture, I really like the bark, and the leaves are beautiful,’” says Garvue. “And they put it in the ground not knowing what it’s going to be like in 30 years.” Which leads to trees that fall onto your roof, or have to be cut in an unappealing “U” because they’ve grown up into power lines.
Indeed, where your utilities are located is the first factor to consider.
According to Barber, large trees (ones that will grow to be more than 40 feet tall) should be planted at least 40 feet away from overhead lines (electric lines being the most crucial); plant medium trees (growing 25-40 feet tall) 15 feet or more away.
Barber recommends having your utility company spray-paint or flag your lawn to indicate where underground utility lines run. This can be requested by contacting the Kentucky Call Before You Dig number, (800) 752-6007, or simply dialing 811. All trees should be kept at least 10 feet away from the underground lines. All tree roots will grow as far as they can, following the path of least resistance. The soil around pipes tends to contract and expand, allowing water to condense on the pipe, and making the soil moister and more attractive to the probing roots.
Large-growing trees should be planted as far away from driveways, curbs, and sidewalks as possible—Barber recommends a minimum of 4 feet. And he says large- and medium-growing trees should be planted 10-20 feet away from building foundations.
Other considerations are whether the tree is suited to your type of soil and drainage, as well as a site’s exposure to sun and wind and the tree’s susceptibility to disease. It’s also worth thinking through what the tree will drop—some people don’t like the mess of cleaning up crabapples or plums; others are annoyed by the percussive dropping of nuts, especially when they put a dent in the new pickup truck.
Barber points out that many cities have lists of trees that are acceptable to plant (and other trees that aren’t approved). Any of the 38 Kentucky communities that participate in the Arbor Day Foundation’s Tree City USA program has a tree board that can be consulted about preferred trees.
Choose orientations that maximize the effect you’re going for—for example, having shade fall on the east and west sides of your house.
And then there are the aesthetic choices—all the multiples of shape, leaf, flower, and bark that a landscaper can use with a painter’s eye.
Will it be a shade tree? Is it providing fall color? Is it supposed to be a specimen tree, considered a standout that attracts attention? Or a foundation one—the plants that provide the framework for your landscaping? What “habit” (typical growth pattern) are you looking for? In other words, what look do you want—sweeping boughs, or weeping ones? Is the overall shape vaselike, columnar, or round? Are you looking for flowers, or ornamental bark?
Choose a tree that speaks to you and it will also shade and enrich future generations.
FOR SMALL TO MEDIUM LOTS
Botanical Name: Carpinus caroliniana
Height: 20-30 feet
Spread: 20-30 feet
Foliage: Thin, simple, dark green leaves that turn various colors.
Care needs: Needs moist soil; does well in shade; difficult to transplant.
Purpose: Shade; fall color; street tree (a tree that is hardy enough to thrive in an urban environment or along a street)
This native tree is known as “musclewood,” from the sinewy appearance of its blue-gray trunk and stems, as well as “ironwood.” Tony Nold, owner of The Plant Kingdom in Louisville (with his wife Shelly, this magazine’s garden columnist), calls it “a good, tough urban tree.” Kristopher Stone of the Boone County Arboretum calls it a good smaller alternative to beech (it has similarly smooth bark).
Botanical Name: Cladrastis kentukea
Height: 30-50 feet
Spread: 40-50 feet
Foliage: Compound leaves have 7-11 alternately spaced leaflets; clusters of white flowers appear every 2-3 years; turns yellow in the fall.
Care needs: Best growth in full sun to partial shade; needs pruning to form strong branch angles, but should be pruned only in the summer.
Purpose: Shade, specimen tree (a tree you select for some unique characteristic that appeals to you or particularly compliments your site; is planted alone in a landscape to stand out for its particular merits, i.e., good shade, great shape, great fall color, interesting bark, spectacular flowering).
Not just native, but Kentuckian through and through—check out the botanical name; the tallest example in the country is in Jefferson County. While it’s rare in the wild, it’s easy enough to find in nurseries, and has many fans among horticulturists (it was a 2004 Theodore Klein Plant Award winner). It’s tolerant of Kentucky’s limestone-based soils; its leaves turn yellow after many other trees have already defoliated. Fun fact: Indians used its wood to make a yellow dye.
Japanese tree lilac
Botanical Name: Syringa reticulata ‘Ivory Silk’
Height: 20-30 feet
Spread: 15-25 feet
Foliage: Simple leaves 3-6 inches long; fragrant white flowers bloom in early summer; poor fall color (brownish-green).
Care needs: Best in full sun in moist, well-
drained soil, but adaptable to many soil conditions.
Purpose: Street tree, specimen tree, flowering tree
This tough plant is considered to be the most trouble-free of lilacs. It blooms early in its life, and profusely, in large terminal clusters. Stone prefers a less-used variety called China Snow Pekin Lilac (syringa pekinensis)—it has a mahogany red bark that peels off in curls that he prefers to the bark of the Japanese.
Botanical Name: Asimina triloba
Height: 15-20 feet
Spread: 15-20 feet
Foliage: Long, thick, drooping leaves; turns yellow in the fall; purple flowers.
Care needs: Moist, slightly acidic soil; does well in full sun or shade.
Purpose: Shade; fruit; street tree
This native tree produces a fruit that’s universally described as “custardy.” Tony Nold calls its foliage “tropical-looking” (it comes from a tropical family). It’s known for attracting butterflies. In its native habitat, it forms suckering colonies from its roots. Kentucky State University is a leading center of research on the pawpaw, which may have potential uses in cancer therapy and as an organic insecticide.
Botanical Name: Magnolia virginiana
Height: 15-25 feet
Spread: 10-20 feet
Foliage: Elliptical leaves stay green for most of the year; creamy white, lemon-scented flowers, smaller than those of other magnolias, bloom in late spring and occasionally during the summer.
Care needs: Wet to swampy soil, full sun to partial shade; needs acidic soil.
Purpose: Specimen tree; screening
Another tough urban tree, with good drought resistance. It sometimes takes on a low, multi-trunked, shrublike appearance. Stone likes the ‘Northern Belle’ cultivar, which he says is more upright and narrower than other sweetbay magnolias and is especially hardy in the cold (it keeps its leaves well below zero).
FOR LARGE LOTS
Botanical Name: Taxodium distichum
Height: 50-70 feet
Spread: 20-30 feet
Foliage: Short, soft needles that emerge bright yellow-green, darken in the summer, and turn russet in the fall.
Care needs: Full sun; prefers wet soils but will adapt to dry; prefers acidic soil.
Purpose: Shade tree, screening
This is one of several conifers that shed their needles. In the wild, they can top 100 feet tall; in very wet settings, they grow the unique extra roots called “knees” that are believed to help anchor them to the soil. The pond cypress, Taxodium ascendens, is a related tree that Stone believes has “an even more fine-textured look and more narrow growth habit to it” than the bald cypress but is used less often.
Botanical Name: Ginkgo biloba
Height: 40-80 feet
Spread: 30-40 feet
Foliage: Distinctive emerald green, fan-shaped leaves turn brilliant golden yellow in fall.
Care needs: Adaptable, but does best in full sun; prefers deep sandy soils and moderate moisture.
Purpose: Street tree, specimen tree, shade
This Chinese native is the only survivor of a prehistoric order of trees, kept alive into our time by being tended in Buddhist temple gardens. You want to get a male tree: the female has an unpleasant odor (it’s prohibited to plant female ginkgo trees in public right-of-way easements or along roads in a number of cities, including Louisville and Lexington). “They’re such darn tough trees,” says Stone—drought-tolerant and well-suited to urban areas. The ginkgo’s eccentric branches usually spread into a rounded form, but there’s a narrow variety
(or cultivar) called “Princeton Sentry.”
Green Giant Arborvitae
Botanical Name: Thuja (standishii x plicata) ‘Green Giant’
Height: 40-60 feet
Spread: 10-15 feet
Foliage: Thin delicate needles, densely packed.
Care needs: Adaptable to many soil types; needs little pruning.
This hybrid grows tall, narrow, and fast: Kristopher Stone cites one at the Boone County Arboretum that was 4 or 5 feet tall in 2002 and is now 35 feet. It has a stately, narrow, formal shape—Stone compares it to an upside-down ice cream cone. Maintains dark, green color, and its foliage has a dark green color and is slightly shiny.
Botanical Name: Zelkova serrata
Height: 50-80 feet
Spread: 40-50 feet
Foliage: Pointed, elliptically shaped leaves; fall color can be showy, with a mix of red, orange, yellow, and purple.
Care needs: Prefers full sun and well-drained, deep, moist soil; adaptable to wide range of pHs.
Purpose: Shade tree, street tree
This vase-shaped tree, with its upright arching limbs, is used widely as a substitute for American elm. The bark can exfoliate in a pattern that shows the orange inner bark peeking through. It’s highly drought-tolerant. Look for individuals with well-spaced limbs to ensure strong branching (the limbs have a tendency to clump together at a single point on the trunk).
Swamp white oak
Botanical Name: Quercus bicolor
Height: 50-60 feet
Spread: 50-60 feet
Foliage: Shiny, dark green leaves that turn yellow and red; 1-inch oval acorns.
Care needs: Grows in wet or dry soils; prefers acidic pH.
Purpose: Shade, specimen, interesting bark, fall beauty
White oaks are a more disease-resistant group of oaks, and this native oak is one of the faster-growing. It’s ice- and windstorm-resistant (surviving the storms of 2008 and 2009 quite well) and tolerant of high-pH soils. The exfoliating gray-brown bark on its branches provides excellent winter interest, and it’s long-lived (lasting up to 300 years).
The Glasgow Garden Club created a brochure celebrating last year’s Arbor Day with photos and sightseeing directions to 22 of the oldest and most unusual trees in Glasgow. The largest white ash in Kentucky is located at 1101 South Green Street. For a brochure or more info, e-mail firstname.lastname@example.org.
Boone County Arboretum has a vast number of tree collections. Download a visitor’s guide at www.bcarboretum.org/VisitorsGuide.aspx.
Join in for the Dogwood Dash 5K Run/Walk on Saturday, April 16, 9 a.m. Call to register. Don’t miss the Spring Plant Sale, May 14, 9 a.m.–noon, for great bargains on perennials, shrubs, and trees. And learn how to identify spring trees and shrubs on May 26, 1:30–3 p.m.
For more information go online to www.bcarboretum.org and look under “Events & Education” or call Laura Kline (859) 586-6101.
KEYWORD EXCLUSIVE: >ONLINE TREE KNOWLEDGE
For more tree recommendations and research, go to Online Tree Knowledge where you find four Web sites that will help you find the right tree for you.