What You Need to Know About Illinois Oak Trees

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oak tree

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Depending on the source, the Quercus genus contains between 500 and 600 species worldwide. That yields a lot from which to choose. At least 60 species grow in North America, with the white oak designated as Illinois’ state tree.

Often, oaks anchor plant communities around which interactive mini-ecosystems thrive. They provide shade and shelter to understory plants, small and large mammals, birds, and insects. Squirrels and birds eat small nut varieties, while deer, turkey and boar eat larger acorns. Birds and small mammals nest in the protective canopy, and ubiquitous insects provide food for the birds and help in pollinating the oak’s flowers.

SEE MORE: Outstanding Oak Tree Facts

Oaks produce both male and female flowers. The male flowers grow in clusters called catkins. Oaks produce much smaller female flowers. At a seminar I recently attended, Des Moines Botanical Garden director Kelly Norris said that oak trees support 534 butterfly and moth pollinators.

Being difficult to transplant, do not try digging them in the wild and hoping for success. You will be disappointed with the results. Save time and buy a tree from a reputable nursery. Most of the varieties common to Illinois grow very large, so site selection needs to be researched. Look up and out. In 20 years, will the branches be colliding with the house or power lines? What about 50 years?

Once you pick a good spot in full sun, follow normal tree-planting instructions. You won’t find a better time for planting than autumn, when we enter a time of less stress from heat – meaning less supplemental watering. Dig the hole at least twice as wide as the root ball. Find the root flare on the trunk, and make sure it is above ground. You may have to remove some soil from around the trunk to locate the flare. Your oak should not look like a utility pole going into the ground. Remove anything that is not tree and roots, such as wires, strings and pots. Backfill the hole with the same soil you removed when digging the hole, and water in well. There you go. You have an oak tree and a three-year commitment to keeping it watered during dry times.

White oak (Quercus alba) lives long, exhibits beautiful scarlet foliage in the fall, reaches 50 to 80 feet tall, and grows relatively slowly. In fact, white oaks comprise many of the historic landmark trees in the northeastern United States.

SEE MORE: How to Plant an Oak Tree in 4 Simple Steps

Another hardy to Illinois oak, the bur oak (Quercus macrocarpa) tolerates drought and adapts to a variety of habitats. It reaches 50 to 80 feet high and up to 90 feet wide in ideal conditions. The decorative fringing on the acorns makes it a popular tree.

Chinkapin oak (Quercus muehlenbergii) also adapts well to a variety of growing sites including mountains, desert canyons and flood plains. It tolerates alkaline soil better than other large oaks, making it a good choice for many places in Illinois.

Ask the Expert


Q. What is diatomaceous earth? I’ve seen it listed as an organic pesticide.
A. It’s the fossilized remains of aquatic organisms in powder form. The sharp edges cut soft-bodied organisms like slugs, and dries out insects with exoskeletons. Wear a facemask when spreading, as it can be harmful to lungs.

Q. My 5-year-old wisteria vine hasn’t bloomed. Should I replace it?
A. No, wisteria takes 7 to 10 years to get established and start blooming. For future reverence, a variety called Kentucky wisteria blooms much faster, but is not as large.

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