Trees that thrive in clay soils include Norway maple, balsam fir, white hickory, hawthorn, black walnut, European larch, aspen, linden, and elm. Many pine species also do well when planted in clay soils.
Proper site preparation is essential if trees are going to grow well in clay soils. Incorporating organic material into the soil provides it with both aeration and nutrients. Because clay soils tend to be alkaline, acidifying the soil may be necessary when planting trees requiring lower pH levels. The planting hole should be roughly twice as wide as the tree's root ball.
For best results, the backfill should be composed of two-thirds original soil and one-third organic material. Compost, wood chips and peat moss can be used as organic material and should be mixed thoroughly with the original soil in order to ensure optimal drainage.