The following lists feature trees and shrubs hardy to at least USDA zone 4; some are hardy further north. They should grow well in clay soils, providing special requirements such as soil pH are also met. Clay soils are usually alkaline with pH ranging from 7 to 8.5. Have the soil tested if you are considering plants with specific pH preferences, then select plants that will thrive in your soil conditions. Acidifying soil must be repeated annually and is not effective when tree roots spread beyond the treated area. The ideal pH range for plants that need acidic soil is 4.0 to 6.5.

Proper planting is critically important if you want healthy, vigorously growing trees and shrubs.

Dig a hole twice as wide as the rootball. If you're planting a tree or shrub with a main trunk, gently brush soil away from the stem to find the first root closest to the soil surface. Adjust the soil depth in the planting hole so the first root will be just below the soil surface when you refill the hole.

If the soil is particularly heavy, both trees and shrubs benefit from being planted so the top of the rootball is slightly higher than the adjacent ground. The optimum amount to raise the rootball depends on its depth. Add soil to the bottom of the planting hole so the plant's rootball, when positioned, will be raised above the adjacent soil level by one inch for every eight inches of rootball depth. Following are some examples:

Rootball depth	Amount to raise rootball
8 inches	1 inch
12 inches	1.5 inches
16 inches	2 inches
24 inches	3 inches

The next step is to fill the hole. If you wish, add compost, peat or composted woodchips to replace up to 1/3 of the original soil volume. Mix the organic matter thoroughly with the clay soil. Never replace all the original soil with black dirt, compost or sand, as distinctly different soils drain unevenly. For proper drainage, it is vital that the soil you use for backfill consists mostly of original soil.

Fertilizer may be incorporated into the backfill soil at planting time. Use a slow-release, balanced fertilizer, such as Osmocote 10-10-10, to prevent injury to the roots and provide nutrients over the entire growing season.

Click on the links below for more information.

USDA Zones in Minnesota

Trees for clay soils

Shrubs for clay soils

The author wishes to thank Dr. James B. Calkins, University of Minnesota Department of Horticultural Science, for his assistance.