Successful Planting in Clay Soil
There is no doubt about it, planting in clay soil can be backbreaking work! Clay soil is heavy to dig, slower to warm in the spring, and can get easily waterlogged. The fine particles sit closely together, restricting air and water movement in the soil. The benefit to clay soil is that it is nutrient-rich, and holds moisture well.
In Michigan, heavy clay soil is prevalent. By selecting the right plants and using correct planting practices, we can still create beautiful landscapes.
When planting or working in the landscape, reduce compaction of the soil by staying out of the garden when it’s wet. Consider planting in raised beds. The soil warms faster in the spring, and the soil drains more easily. If raised beds are not an option, stepping stones help reduce compaction in beds. They guide foot traffic away from tender plant roots, and add charm.
Be sure to dig the planting hole twice as wide as the rootball, but only to the same depth as the pot or rootball. Digging too deeply can cause the plant to sink over time, causing the plant to be too low. According to the University of Vermont Extension Department of Plant and Soil Science, this is a major cause of woody plant demise after a few years. If the soil is particularly heavy, trees and shrubs benefit from being planted so the top of the rootball is slightly higher than the surrounding ground.
Amend 1/3 of the backfill soil with a good compost to add nutrients and improve drainage. In existing beds, top-dress with one inch of compost. There is no need to till. Worms, insects, and microorganisms will take the material down into the soil for you, improving the soil structure as they do so. Mulch the beds to prevent the soil from cracking and slow drying out.
I have found that it is much easier, and more successful to select plants to fit the conditions of the planting site, than to change the site to fit the plants. Perennials suitable for clay soil include daylily, hosta, coneflower, black-eyed susan, joe-pye, select varieties of fern and ornamental grass, brunnera, goatsbeard, false sunflower, ligularia, astilbe, butterfly weed, baptisia, Russian sage, alliums, bee balm, and hardy hibiscus.
Shrubs that will tolerate clay soil include chokeberry, shrub dogwood, forsythia, ninebark, willow, viburnum, elderberry, select varieties of hydrangea, wigelia, summersweet, sweetspire, rose of sharon, and spirea.
Tree selections for clay include river birch, magnolia, hawthorn, honeylocust, oak, ornamental pear, linden, amelancher, arborvitae, ginko, and select varieties of maple, fir, and pine.