Working with clay soils can be strenuous, resulting in frustration when planting trees and shrubs that are clay-intolerant. Because this type of soil has a hard texture, it's important that gardeners choose clay-tolerant trees and shrubs for clay soils. According to the University of Minnesota Extension website, some common trees suitable for clay soils include aspens, cottonwoods, balsam firs, maple varieties and elms. Shrubs that are clay-tolerant are lilacs, snowberries, honeysuckles, willows and others.
Clay soils, also called "heavy soils", have a large amount of clay particles that bind together. Because the numerous fine clay particles bond together so easily, the soil is prone to compaction, which makes digging difficult for gardeners. This type of soil is sticky and similar to plaster. A clay soil's flat particles also cause the soil to have limited air spaces.
Despite the challenges of clay soils, they do have some good qualities. On a positive note, this type of soil has good moisture retention, which helps plants during droughts and prevents the escape of valuable nutrients, such as nitrogen and potassium, obtained during rainfall or irrigation. Clay soils are also exceptionally rich in minerals that enable plants to grow well.
Clays come in various colors that have different qualities, including shades of browns, grays, greens, blues, yellows and near-black. Darker clays are typically higher in organic matter and work better for growing than lighter clays. Gray or blue clays need to be loosened for supporting healthy plant growth as they have poor aeration. Red-colored clays, such as those found in the Southeast, have good aeration and make a loose soil that drains well.
The texture and workability of clay can be improved by adding grit and large quantities of organic matter that is well-rotted. Doing so enables the clay soil particles to form crumbs and small granules. As a result, clay soil supports many types of plants.
When a clay soil is moist, a spading fork should be used instead of a spade or shovel. Large clumps that are turned over while working the soil should be exposed to air and sun. Once they have completely dried, a fine-mist spray helps to soften them. Some clay soils are helped by fall tilling, which helps to loosen soil and make it fluffy in spring.
Because most clay soils don't drain freely, it takes longer for water to infiltrate them. Clays should not be worked when wet since wet clay soil causes water to run off. Peat moss is not recommended for clay soil because it makes a flowerbed soggy and results in plants decaying.