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Pinpointing the Problem with Pin Oak
This article was published originally on 7/11/1997Here's a commonly heard problem on the ISU Hortline: "I have a beautiful pin oak in the front yard--it's been there for almost 25 years. And now it's starting to die off and the leaves look terrible. What can I do?"
On most Iowa soils, probably the best course of action would have been to never have planted pin oak in the first place. While this homeowner thought they were planting for posterity, what they really planted was a problem tree that will cost them significant headaches for the life of the tree.
Pin Oak (Quercus palustris) does poorly on our clay-rich, poorly drained soils. Pin oak prefers moist, rich, well-drained, acidic soil, and is extremely intolerant of high pH soils. In appropriate soils, this tree can reach 70 to 100 feet and has an attractive pyramidal form with glossy dark green leaves.
When planted in soils with a pH greater than 7.5, however, the pin oak develops iron chlorosis, a nutrient deficiency symptom. (Other trees quite susceptible include silver maple, baldcypress, crabapple, and sweet gum.) Affected trees have yellow leaves with dark green veins, with some developing angular brown spots and brown, curled leaf margins. In severe cases, leaf color may change from yellow to white to brown. After suffering from chlorosis for a period of years, branches and twigs may begin to die. Chlorosis is often most severe in areas where topsoil has been removed, exposing clay subsoil, as in new housing developments.
Usually, there is plenty of iron in the soil, but high soil pH prevents the iron from being absorbed by the plant. Since iron is essential for production of chlorophyll, the tree fails to produce enough chlorophyll to maintain healthy green leaves. Lack of available iron can be magnified by low soil temperatures; high soil moisture; large amounts of copper, manganese, or zinc; or excessive application of phosphorus.
What are the alternatives to a lifetime of feeding a pin oak? First, choose plants suitable for your soil. There are several attractive oaks which do much better in typical Iowa soils. Recommended species include chinkapin oak (Q. muehlenbergii), English oak (Q. robur, cultivars 'Fastigiata' or 'Wandell'), or red oak (Q. rubra). Below are some common shade trees found in Iowa and their preferred soil pH ranges.
Preference of certain species of trees for various soil pH levels
If however, you have a yard with an established pin oak, there are some possible treatments for addressing soil chlorosis, though they can be expensive and/or time-consuming. There are three primary methods for treating iron chlorosis due to alkaline soil:
Dealing with iron chlorosis in the home landscape can be a daunting task, but by doing a little extra research to place the right plants for the site in the first place, homeowners can ensure they'll enjoy attractive, healthy trees for years to come.
Year of Publication:
IC-477(18) -- July 11, 1997