January 28, 2016 – Kenosha News
This is the second of a series of columns looking at options to replace ash trees killed by emerald ash borer. Last week I highlighted maples. Oaks are next on the list.
English oak and several oak hybrids (crosses of two or more oak species) are prospective replacements but I’ll focus on suitability of oaks native to southern Wisconsin.
White oak is slow growing and performs best on moist well-drained soils. It is difficult to find in nurseries and should be transplanted balled and burlapped as a small tree. Fall color is dark reds. Established trees are sensitive to, and may be killed by, soil compaction associated with building and road construction.
Bur oak is easily identified by its fringed acorn cap and thick corky bark, which helped protect the tree from prairie fires. Bur oak stands out in the winter landscape with its massive picturesque form. Like their close relative white oak, bur oaks are difficult to transplant. Bur oak should be planted in large landscapes because they will reach 70 to 80 feet high and wide.
White oaks and bur oaks are planted for future generations. Landowners who build homes in white and bur oak woods should be very careful during siting and construction to minimize impact on the trees. Existing trees should be cared for as part of our natural heritage.
Swamp white oak is another slow grower but easier to transplant than white and bur oaks. It is a better choice for urban areas with neutral to acidic soils and on wet sites. Swamp white oaks have interesting corky bark covering their trunk, branches and twigs.
Chinkapin oak has rounded lobed leaves. Fall color is yellow to orange-brown. It adaptable to urban conditions including higher soil pH. Chinkapin is moderately slow growing and may be challenging to transplant.
Red oak, which has pointy leaf tips, is fast growing and easy to transplant. Although it prefers well-drained acidic soils, red oak adjusts well to higher pH, urban soils. Red oak’s dark green leaves turn russet-red in fall.
Pin oak is widely planted because of its wide availability. It is easy to transplant and has good red fall color. However, it is not a good choice for Midwestern urban, alkaline soil sites because it often develops nutrient deficiency chlorosis.
For lists of recommended replacement trees and last week’s column on maples, please visit: Gardening Questions.
Barb Larson is horticulture educator for the Kenosha County University of Wisconsin Extension. She holds a master’s of science in horticulture from the University of Wisconsin-Madison. If you have a plant or gardening question, email her at firstname.lastname@example.org or call 262-857-1942.