News source/writer: Andrew Holsinger, 217-532-3941, aholsing@illinois.edu

URBANA, Ill. – The splendor of trees and shrubs is apparent in the above-ground portions of the plants, but what lies beneath should not be ignored.

"Soil plays a vital role in the survival of trees and shrubs in the landscape," University of Illinois Extension educator Andrew Holsinger explains.

Placement of trees is vital to their success, especially when planting in wet soils. Soil texture—the relative ratio of sand, silt, and clay in the soil—is a primary factor in soil moisture retention. Soil texture also influences aeration, or how air moves through the soil. Heavy clay soils tend to have poor aeration and drainage.

There are other factors influencing soil moisture that are important when planting trees and shrubs. These include whether there is a hardpan or other soil interfaces that can interfere with root development. Additional reasons for concern are precipitation patterns or poorly timed or located irrigation systems.

Some trees and shrubs have a greater ability to withstand wet soils than others, Holsinger says. "It is much more cost-effective to plant the right species for the location than trying to adjust the site conditions," he adds.

A threat to planting in wet soils is frost heaving. Frost heaving is an upward swelling of the soil during freezing conditions caused by ice formation in the pore spaces of soils. Holsinger recommends planting trees and shrubs in wet sites during the early spring to ensure a full season of growth, which can reduce the likelihood of frost heaving.

Initial decisions about placement of a new tree should be guided not only by the mature canopy, but also the expansion of the root system.

"With varying requirements for moisture, it is easy to select trees or shrubs based on their prior performance," Holsinger says.

Looking at the distribution where trees are located in the wild can guide your thinking when it comes to plant selection. However, species like bald cypress or black gum have more adaptability than their natural distribution would suggest.

"Just because a tree can grow on a wet site doesn't mean that other characteristics shouldn't factor into the selection process," Holsinger says. Insect issues or weak wood should also be considered when selecting trees or shrubs for landscape plantings.