In 1961, the Iowa General Assembly designated the "oak" as Iowa's official state tree. Certainly, prior to that designation and since, discussion has centered around whether a single species of oak should have been Iowa's state tree. Many people have come to recognize the bur oak as Iowa's state tree since it is the only species found throughout the entire state. Most woodlands and all communities have one or more species of oaks as a component. It can be argued that, no other group of trees is more important to both rural and urban forests in Iowa. Twelve different species of oaks are native to Iowa. Iowa oaks are separated into either of two groups: red oaks or white oaks.
The white oaks (white, bur, chinkapin, dwarf chinkapin, swamp white, and post) have lobed leaves with rounded lobes, acorns which mature in a single growing season and germinate in the fall sending down a root system, and have plugs (tyloses) in the water conducting tissue of the wood or vessels, making oak containers such as whiskey barrels waterproof.
- White oak (found in the eastern 2/3 of Iowa) is the most valuable "white" oak for lumber production. It will grow on a variety of sites, from moist cove sites, with deep soil to the drier ridges and southern exposures. Iowa white oaks live to 400 years and the largest white oak in Iowa is more than 57 inches in diameter.
- Bur oak (found throughout the entire state) is the oak of the midwest, very slow growing, long-lived, and adapted to a wide range of sites and soils, from very dry exposures to good soils which are fertile and moist.
- Chinkapin (found in southeast Iowa) is an oak, that does not look like a oak; its leaves are not lobed, but have very coarse teeth without bristle tips. Chinkapin means chestnut, and its leaves resemble the leaves of a chestnut. Chinkapin makes an excellent shade tree and it is very tolerant of dry, high pH soils; it grows naturally on ridges, hill tops and rocky southern exposures.
- Dwarf chinkapin (found in eastern Iowa) has smaller leaves than chinkapin oak and seldom reaches small tree size; it is considered a shrub. It is native to upland sites, often growing on the same sites as chinkapin oak.
- Swamp white oak (found along streams in eastern, central, and south central Iowa) tolerates the moist low-lying sites along streams, has leaves with more shallow lobes, and bark that exfoliates like a birch on small limbs. Swamp white oak is used frequently as a shade tree, but should not be planted on non-acidic soils because it also may suffer from iron chlorosis.
- Post oak (found in Lee, Henry, Van Buren and Appanoose counties) is the least common of the oaks. It is a dry species, often growing on ridges or hot dry exposures. Its leaf shape resembles a cross, with two smaller lobes at the base.
The red oaks (red, pin, black, northern pin, shingle, and blackjack) have mostly lobed leaves with bristle tips at the ends of the lobes, acorns requiring two growing seasons to mature and do not germinate until the following spring, and vessels without plugs.
- Red oak (native except in the far northwest counties) is slower growing, but may be a better choice on non-acidic soils. It is fairly easy to transplant, grows faster than most oaks, and is adapted to a wide range of sites. Red oak is the most valuable of the red oaks for lumber production.
- Pin oak (native to the southeast 1/4 of Iowa) is probably used more as a shade tree than any other oak. It is a bottomland species, tolerates wet and poorly drained soils which are acidic. Pin oak is fast growing, easy to transplant, should be used only on soils which are acidic; on basic (high pH) soils, they often exhibit iron deficiency chlorosis in which the leaves turn yellow and the veins remain green.
- Black oak (found throughout the state except in the far northwest corner) will grow on a variety of sites from very dry upland ridges to deep rich cove sites to dry sandy bottomlands. Black oaks vary greatly in their appearance because of genetic diversity and because they hybridize with other species of red oaks.
- Northern pin oak (found primarily in north central and northeast Iowa) is similar to the red oak but does not get as large. The acorns of the northern pin oak are more oval that the pin oak. It is best grown in moist, well-drained soils but is adaptable to adverse soil conditions.
- Shingle oak (found in the southern 1/3 of Iowa) has a leaf without lobes, but a bristle tip on the tip, prefers acidic soils and will tolerate tough, dry sites. Shingle oak is relatively easy to transplant and has become more common in the urban landscape.
- Blackjack oak (found in far southeast Iowa) has leaves with three distinct lobes, is a small tree rarely exceeding a foot in diameter, and tolerates dry upland soils.
Many species of oaks may be incorporated into our urban and landscape planting. Pay attention to the natural habitat of the oaks when selecting them for landscape use; matching the tree to the site will result in greater success in the landscape. Remember that many of the oak species become very large trees and they need room to develop and grow in the landscape. Avoid large plantings of single species to avoid potential problems with oak wilt. Many of the oaks are difficult to move because of their non-fibrous root habit. Moving smaller stock may improve success because less of the root system is lost.
Diseases that Can Affect Oaks
Insects that Can Affect Oaks