Ask A Master Gardener – The Mighty Oak

Authored by Carol Shirk

In 2004 Congress passed legislation designating the oak America’s National Tree.  The Arbor Day Foundation sponsored a four month long open-voting process offering 21 broad tree categories as options.  From the very first day of voting, the oak was the clear leader.  Oaks are unequivocally the most widespread hardwood, growing in essentially all 48 contiguous United States.  They are prized for their beauty, shade, wildlife contributions, and economic value.

Oak is in the genus Quercus and of the more than 600 species known to exist, nine are native to Wisconsin.  They can broadly be divided into two categories: red and white.  The red oak group has leaves with a “V” shaped tips with spiny bristles at the tips.  These acorns mature at the end of two growing seasons and germinate in the fall.  The inside of the nut is wooly or silky and the bark of the tree is grey, black or brown/black.

The white oaks have leaves with rounded tips or “U” shaped with no bristles.  The acorns mature in one growing season, germinate in the spring, and the inner shell is smooth.  The bark is grey or white/grey with shades of cream.

Oak trees are slower growing than many trees, reaching mature height in 20 to 30 years.  However, they have amazing longevity, lasting 200 to 400 years.  Red oaks will grow faster than white.  Both trees can top out at 100 feet under ideal conditions, but 70 to 80 feet is more common with the white oak being slightly smaller.  Red oaks have a spread of 100 feet while white oaks hold steady around 75 feet.

Oak trees provide incredible advantage to wildlife.  They are nesting places for birds and small mammals, the flowers are food for pollinating insects, the acorns provide nourishment for deer, bear, turkeys and other birds, as well as a multitude of small mammals.

Oak trees are not without problems.  Oak wilt is one of the most serious diseases that has caused a setback in the oak population since the 1940s when it was first discovered in Wisconsin.  Red oaks are more susceptible to this fatal fungal disease.  It is transmitted by picnic beetles that are attracted to mats of the fungus that then transport it to open wounds in another tree.  It is imperative to avoid pruning oak trees from April 1 through October 1 when picnic beetles are active.  In addition, if wounds occur naturally via storm damage or other means, cover them as soon as possible with tree wound paint.

If you are going to choose one oak tree to plant in your landscape, consider the burr oak, Quercus macrocarpa.  It is in the white oak category, so is less susceptible to oak wilt.  It is adaptable to a multitude of conditions with nice large acorns.  Check out the state champion in Dousman, Wisconsin at nearly 100′ tall and over 100′ across if you want to see an example of a fine specimen.

If you are a person of my age, you may not live to see the mature tree if you plant an oak.  However, your children and grandchildren will and they will be grateful that you thought ahead.  Invest in the future.  Plant an oak tree and bless the next generation. As George Bernard Shaw wrote, “Think of the fierce energy concentrated in an acorn! You bury it in the ground, and it explodes into an oak!”

Carol Shirk

Certified Master Gardener


Sharing is Caring - Click Below to Share