Trees and Shrubs for Wet Soils

Many trees and shrubs thrive in Iowa's fertile, well-drained soils. Most trees and shrubs, however, don't like wet soils. Fortunately, there are plants that tolerate wet soils better than others. The following trees and shrubs are good choices for wet sites.

Trees

The silver maple (Acer saccharinum) is commonly found along the banks of rivers and streams throughout Iowa. It is one of our largest native trees, growing up to 100 feet tall. Silver maples have been widely planted in the past because they transplant well, grow fast, and adapt to a wide range of site and soil conditions. Unfortunately, silver maples are weak-wooded trees. They often become liabilities in home landscapes because of their tendency to break apart in ice and windstorms. While the silver maple is a poor choice for the home landscape, it is suitable for windbreaks and natural areas.

River birch (Betula nigra) tolerates heat and drought better than the white-barked birches. It is also resistant to the bronze birch borer. The river birch is native to much of the eastern third of Iowa. It is typically found in moist to wet areas along rivers, hence the common name river birch. The exfoliating bark varies from gray-brown to reddish brown. The cultivar 'Heritage' has a salmon-white bark. River birches are often planted as multi-stemmed specimens or "clumps." It grows 50 to 60 feet tall. River birches perform best in acid soils. Their foliage often turns a sickly yellow-green in alkaline soils.

The American hornbeam (Carpinus caroliniana) is native to woodlands in eastern Iowa. It is noted for its hard, tough wood. The American hornbeam is also referred to as ironwood, musclewood, and blue beech. The small, shrubby tree grows slowly to a height of 20 to 30 feet. It does well in heavy shade and wet soils, but will tolerate sunnier and drier sites. In the fall, the foliage turns yellow to orange red.

Another large, native tree is the hackberry (Celtis occidentalis). Though it can be found in a wide range of habitats, it is most often found in the floodplains of rivers and streams. Although hackberries don't possess any outstanding ornamental feature, they are adaptable. They tolerate acid or alkaline soils, wet or dry sites, and harsh urban conditions. Hackberries usually grow 50 to 60 feet tall, but can grow 100 feet tall.

The green ash (Fraxinus pennsylvanica) is one of our most common native trees. It is also widely planted because of its adaptability and fast growth rate. The green ash grows well in both wet and dry soils. Its mature height is approximately 50 to 60 feet tall. Unfortunately, it is weak-wooded and susceptible to storm damage. Seedless cultivars, such as 'Patmore' and 'Bergeson,' are preferred for home landscapes. Another excellent cultivar is 'Summit.' 'Summit' has an upright growth habit, but does produce a few seeds. An invasive pest called emerald ash borer has become a serious pest for this species and because of this insect, this tree is no longer recommended for planting in Iowa. [Note: Green Ash is no longer a recommended species for Iowa due to the prescence of Emerald Ash Borer.  When this article was published, this insect pest was not yet introduced to the state]

One of our most distinctive native trees is the sycamore (Platanus occidentalis). Its large maple-like leaves, persistent seedballs, exfoliating bark, and huge size make it easy to identify. The sycamore is not a tree for a small yard as it may eventually reach a height of 75 to 100 feet. It is best suited to parks and other large open areas. Anthracnose (a fungal disease) is a problem in cool, wet springs. Severe anthracnose infestations cause heavy leaf drop in late spring.

Swamp white oak (Quercus bicolor) is a large, slow growing oak which may eventually attain a height and spread of 60 feet. While difficult to locate in nurseries, it is sturdy, drought tolerant, and makes a handsome shade tree. The swamp white oak performs best in moist, acid soils.

Originally found only in southeastern Iowa, the pin oak (Quercus palustris) has been widely planted across the state because of its pyramidal habit and ease of transplanting. Unfortunately, iron chlorosis is a serious problem in alkaline soils. Chlorotic foliage is a sickly yellow-green. The pin oak is not a good street tree because of its drooping lower branches. Fall color varies from bronze to red. It grows 60 to 70 feet tall.

Bald cypress (Taxodium distichum) is a deciduous conifer. Native to swamps in the southeastern United States, it does surprisingly well in the north. In Iowa, it performs best in the southern portion of the state. The foliage is an attractive yellow-green in the spring and turns to russet in the fall. The bald cypress possesses a pyramidal growth habit and may eventually reach a height of 50 feet.

Other trees that do well in wet soils include the cottonwood (Populus deltoides), alders (Alnus species), black tupelo (Nyssa sylvatica), and willows (Salix species).

Shrubs

Red chokeberry (Aronia arbutifolia) is an upright, suckering, multi-stemmed shrub that grows 6 to 8 feet tall. Red chokeberry is noted for its red fruit in late summer and fall. Leaves turn a reddish purple in fall. The variety 'Brilliantissima' produces excellent fall foliage color (scarlet) and a large crop of glossy red fruit.

A native shrub, buttonbush (Cephalanthus occidentalis) is typically found along stream banks, lake shores, and other wet areas. The shrub has glossy green foliage and produces creamy- white flowers in globular heads in August. Its mature height is about 6 feet, though it can grow up to 12 to 15 feet in southern areas of the United States.

Although not widely planted, summersweet clethra (Clethra alnifolia) is an excellent shrub for the home landscape. It is native to wet areas and will grow in full sun or heavy shade. Summersweet clethra produces small, white, fragrant flowers on spike-like structures. The flowers appear in mid-summer and remain attractive for 3 to 4 weeks. Bees and butterflies find the flowers irresistible. The foliage of summersweet clethra is a lustrous, dark green. In the fall, the leaves turn to a pale yellow or golden brown. Plant size is variable and determined by soil and moisture conditions. Summersweet clethra can grow to 3 to 8 feet tall and 4 to 6 feet wide. The cultivar 'Rosea' produces pink flowers which fade to pinkish white. 'Pink Spires' produces rose- pink flower buds which open to soft pink.

Silky dogwood (Cornus amomum) is a native shrub commonly found along streambanks, wet prairies, and at the edges of bottomland woods. Silky dogwood produces flat- topped clusters of yellowish white flowers. Fruit is bluish with white blotches. Silky dogwood is a rounded shrub which grows approximately 6 to 10 feet tall with a similar spread.

Another native dogwood is redosier dogwood (Cornus sericea). It grows about 6 to 8 feet tall. The redosier dogwood is noted for its red-colored twigs in winter. Several varieties are available. 'Cardinal' is an introduction from the University of Minnesota Landscape Arboretum. Its twigs are bright red in winter. 'Isanti' and 'Kelseyi' are compact, red-stemmed shrubs. 'Flaviramea' has yellow stems.

Winterberry (Ilex verticillata) is a deciduous holly. The deep green leaves drop off in the fall revealing bright red fruit. The shrub attains a height of 6 to 10 feet. Hollies are dioecious. Male and female flowers are produced on separate plants. The cultivars 'Sparkleberry,' 'Winter Red,' and 'Christmas Cheer' produce abundant bright red berries. A male cultivar, such as 'Southern Gentleman' or 'Jim Dandy,' is required for pollination. Winterberries do require acid soils.

Purpleosier willow (Salix purpurea) is an 8 to 10 foot shrub. 'Nana' is a compact form which grows about 4 feet tall. 'Streamco' is a Soil Conservation Service, USDA introduction which was developed to prevent soil erosion along stream banks. The purpleosier willow is one of many willows that grow well in wet soils.

American elder (Sambucus canadensis) is a native suckering shrub that produces large clusters of purple-black fruit in late summer. The ripened fruit are good for jellies, preserves, and wines. The fruit are also attractive to birds. Its mature height is 6 to 10 feet. 'Aurea' and 'Laciniata' are two cultivars which have greater landscape potential than the species. 'Aurea' has golden-yellow foliage and red fruit, while 'Laciniata' has cutleaf foliage.

Virginia sweetspire (Itea virginica) and common sweetshrub (Calycanthus floridus) are two additional shrubs that do well in moist to wet soils.

When selecting trees and shrubs for the home landscape, gardeners should select plants suitable for the site. Wet sites can be a challenge. However, the aforementioned trees and shrubs will perform well in wet soils.

This article originally appeared in the August 7, 1998 issue, p. 108.