The Best Trees for High Alkaline & Hard Clay Soil
While low pH levels and clay soil often seem to go together like peanut butter and jelly, in reality many regions experience hard-packed clay that is actually alkaline rather than acidic. You can neutralize this “lime” or “chalk” soil somewhat with copious amounts of peat moss or chemicals. But it’s much easier to landscape with the many plants which thrive under both hard clay and alkaline conditions. Fortunately, several trees fall into that category, and all are hardy to zones 3 or 4.
Landscapers prize the handsome silver maple for its rapid growth, graceful branch structure, delicate leaves and brilliant yellow foliage in the fall. The tree grows from 45 to 75 feet tall. Its drawbacks, according to garden writer Barbara Damrosch, include easily broken branches and an invasive root system. Damrosch recommends a careful pruning schedule in homeowners promptly remove waterspouts and spindly branches, preferably in late summer or early fall. The tree likes a sunny location with moist soil.
A good choice for erosion control and shade, hackberry thrives where few trees will. Growing as tall as 60 feet, the hackberry grows anywhere from Canada to Texas. Town planners often use it to line streets because of its ability to withstand pollution and drought. It will grow under the shade of other trees, preferring stream beds and other moist places. The U.S. Department of Agriculture admits that while landscapers don’t count the tree as the country’s handsomest, hackberry usually withstands fungal and insect infestations without succumbing to them. The tree bears smallish fruit which, while not fit for human consumption, attracts birds and other wildlife.
Green ash grows quickly to its ultimate height of 40 to 60 feet--much shorter than other ash trees. The green ash shares many features with its bigger brothers, however, including a preference for sunny, moist growing conditions. When pruning and training the tree, encourage a single trunk and remove weak-looking branches.
Although once used extensively for erosion control on American beaches, the Australian pine grows so vigorously that some states now consider it invasive. Check with your extension service before planting it. The dark evergreen tree grows at least 50 feet high and spreads 20 to 30 feet wide. As its former use suggests, Australian pine tolerates salt, wind and other tough conditions, including unusually wet or dry conditions. It grows well in sun or partial shade.
Noted for its graceful, spreading silhouette, the bur oak can grow as tall as 100 feet, although 60 feet is more common. The tree can tolerate neglect and drought, and its deeply-ridged bark and branches offer winter interest, as do its draping, yellowish catkins. The long-lived bur oak also bears unusually large acorns.
Honeylocusts are small but mighty. Although growing only 30 to 60 feet tall, honeylocusts reach that height quickly. Obtain a thornless variety, if possible, and plant it in a sunny, moist location. The hardy tree provides dappled shade and features yellow foliage in the fall.
- University of Minnesota: Trees for Tough Conditions
- University of Minnesota: Trees for Clay Soils
- "The Garden Primer;" Barbara Damrosch; 1988