Extension Communications 3614 Administrative Services Building Ames, Iowa 50011-3614 (515) 294-9915

9/29/03

Contacts:
Chris Feeley, Forestry Extension, (515) 294-6739, cfeeley@iastate.edu
Jean McGuire, Continuing Education and Communication Services, (515) 294-7033, jmcguire@iastate.edu

Yard and Garden Column for the Week Beginning Oct. 3, 2003

Iowa's Oaks

By Chris Feeley
Extension Forester
Iowa State University

In 1961, the Iowa General Assembly designated the oak as Iowa's official state tree. Since that time, discussion has centered around whether a single species of oak should have been selected as Iowa's state tree. Iowa's woodlands and urban 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, although only a single species (bur oak) is found throughout the state.

Iowa oaks are separated into either of two groups: red oaks or white oaks. The red oaks have mostly lobed leaves with bristle tips at the end of each lobe. The red oak acorns require two growing seasons to mature and do not germinate until the following spring. The white oaks have leaves with rounded lobes without bristle-tips. The acorns mature in a single growing season, and germinate in the fall.

Red Oak Group
Red oak (native except in the extreme northwestern 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 southeastern fourth of Iowa) is probably used more as a shade tree than any other oak. It is a bottomland species that tolerates wet and poorly drained acidic soils. Pin oak is fast growing, easy to transplant, and should be used only on soils that are acidic. On basic (high pH) soils, they often exhibit iron deficiency (chlorosis) in which the leaves turn yellow and the veins remain green.

Shingle oak (southern third of Iowa) has a leaf without lobes, but it does have a bristle on the tip. Many people are surprised by the non-lobed leaf shape and confuse this species with willow. Shingle oak 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.

Northern pin oak (northern half of Iowa) looks like pin oak, but has more oval acorns, and is more difficult to transplant.

Black oak (all but extreme northwest corner of the state) 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.

Blackjack oak (the southeast corner of Iowa) has leaves with three distinct bristle-tipped lobes, is a small tree rarely exceeding a foot in diameter, and tolerates dry upland soils.

White Oak Group
White oak (eastern two-thirds of Iowa) is the most valuable "white" oak for lumber production, and it will grow on a variety of sites and soils. Iowa white oaks live to 400+ years and the largest white oak in Iowa is more than 57 inches in diameter.

Bur oak (all Iowa counties) is the oak of the Midwest. Bur oak is very slow growing, long-lived and adapted to a wide range of sites and soils.

Swamp white oak (along streams in eastern, central and south central Iowa) tolerates the moist, low-lying sites along streams, has leaves with 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.

Chinkapin (found in southeast Iowa) is an oak, that does not look like an oak. The leaves are not lobed and have very coarse teeth without bristle tips. Chinkapin means chestnut, and its leaves resemble the leaves of a chestnut tree. Chinkapin makes an excellent shade tree and it is very tolerant of dry, high pH soils.

Post oak (Lee, Henry, Van Buren and Appanoose counties) is the least common of the oaks. It is a dry soils species, often growing on ridges or hot, dry exposures. Its leaf shape resembles a cross, with two smaller lobes at the base.

Dwarf chinkapin oak (eastern Iowa) has smaller leaves than chinkapin oak and seldom reaches small tree size. It is native to the upland, growing on the same sites as chinkapin oak.

Many species of oaks can be incorporated into urban landscapes. Before selecting an oak for your yard, consider the site and soil requirements of the tree and match the species to your yard. Also, remember that most oak species become very large trees and need room to develop and grow in the landscape. More information on Iowa's native trees can be found at http://www.extension.iastate.edu/pages/tree.

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Editors: Five color photos, suitable for publication, are available at right. Click on each thumbnail photo to go to the fullsized photo. The first picture's fullsize photo is 276K; the second picture's fullsize photo is 336K; the third picture's fullsize photo is 348K; the fourth picture's fullsize photo is 264K; and the fifth picture's fullsize photo is 240K. Caption: Black Oak
Caption: Chinkapin Oak
Caption: Post Oak
Caption: Shingle Oak
Caption: Swamp White Oak

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