January 18, 2007 at 7:39 a.m.
A well-grown oak is an asset to any landscape. Its presence is felt year-round. The leaves offer summer shade and fall color that persists into the winter. The acorns are a valuable fall food source for many wildlife species.
Most oaks grow best in fertile, acidic soil in full sun, but will tolerate lighter, sandier soil and dry conditions. They are tricky to transplant, making them hard to find in the nursery trade. Root pruning and container growing have made them more available and easier to transplant. Seedlings are fast growing, so don't hesitate to plant an acorn where you want a tree. Plant it in the fall or store it in moist soil in a cool place over the winter and then plant in the ground in the spring.
There are several species of oaks native to the upper Midwest. The problem for our area is that many of them are more suited to zone 4 which could be a problem. When choosing a species, keep in mind its mature size and soil requirements.
The white oak is native to well-drained, acidic soils. It grows 50 to 75 feet tall, with a spread of 40-60 feet. White oak has broad, rounded top and irregularly spreading limbs. The leaves, which don't fully unfold until mid-May, are deeply divided into 5-9 fingerlike, rounded lobes. They are bright green in summer, turning deep red or violet-purple in fall. It is considered a zone 3 tree.
The swamp white oak is found on wetter sites. It grows 40-65 feet tall and has an open, rounded crown. It transplants fairly well and is usually available bare root, balled and burlapped, or in containers. This tree has few insect or disease problems. It is recommended for zone 4. Plant it in full sun and give it room to spread. As with most trees, providing a generous area of organic mulch and protecting the trunk from mechanical damage will encourage good growth.
Northern pin oak is found on drier, sandier sites. It is smaller, growing 45-65 feet tall. Fall color is deep red to reddish brown. It will suffer from chlorosis on soils with too high of a ph, but the problem is easily corrected by adding iron to the soil to lower the ph. It is susceptible to oak wilt and is a zone 3 tree.
The pin oak is native to moister soils. It grows 65 feet tall or more with a spread of up to 50 feet. It is easier to transplant than most oaks and has outstanding fall color and a good pyramidal form, making it better adapted to landscape use. It requires acidic soil and is a zone 4 tree.
The bur oak is native on drier sites. It is a type of white oak with leaves that are shaped like bass fiddles. It grows 50-80 feet tall and makes an impressive specimen in a savanna setting. It is adaptable to various soils and more tolerant of city conditions than other oaks, but it can be difficult to transplant. It is too large for most city landscapes, but is a good choice for rural and large suburban sites through zone 3.
The red oak is native to a variety of habitats and soils. It grows 50-80 feet tall and has pointed leaves. It is faster growing than other oaks and easier to transplant. The dark green leaves turn to shades of red in the fall that persist into the winter. It prefers sandy loam soils that are well-drained and acidic. It will iron chlorosis in high ph soils. It is tolerant of city conditions, but is very susceptible to oak wilt. If you have a red oak on your property, it is definitely worth some effort to keep it healthy. Although it is a zone 4 tree, there are many red oak in our area.
The scarlet oak is native on drier sites. It is a type of red oak that will grow 50-75 feet tall with an irregular open crown. Leaves are shiny, dark green, turning scarlet to brownish-red in the fall. Another zone 4 tree, it will tolerate a dry, infertile soil as long as it is acidic. A good landscape tree, it is a relatively fast grower with a good form.
Black oaks are native to sandy soils. They grow about 60 feet tall and have an open crown. Fall color is dull red to orange-brown. This zone 4 tree is worth seeking out.
Portions of this article were taken from a book by Lynn Steiner called "Landscaping with Native Plants of Wisconsin". It will be available in April 2007.