The Majestic Oak

Along with maple, the tree that most Wisconsinites can identify is the mighty oak.  My entirely unscientific research turned up hundreds of poems written about oak trees, almost as many as are written about love and love lost.  Often people will leave an oak standing in an inconvenient location rather than fell it.  In 2004 Congress passed a bill making oak our national tree.

        What is our fascination with oaks?  Is it that they can stand for centuries?  Is it their massive size?  Their beautiful form?  Maybe it’s an innate in geo-ecological memory.  Before Europeans arrived in Wisconsin and began covering the state with farms fields and roads, and later parking lots,  sprawling buildings and huge grass lawns, a large part of our state was what’s known as oak savanna, a lightly forested grassland where oak was the dominant tree species.  South of a line from Grantsburg in northwest Wisconsin to Manitowoc in the east, oak savanna reigned, except for along the Lake Michigan shoreline.  Sadly, today oak savanna is one of the rarest plant communities on earth.

        There are almost 100 different species of oak native to the United States. They occur naturally in all 48 contiguous states except, oddly, Idaho.  Probably the oak most people can identify is the white oak, whose leaves have the classic round-lobed shape.  The bur oak, one of the white oak group, is the most common oak native to the Midwest.  Many people also know red oak and black oak, whose leaves have sharply pointed lobes similar to those of maples.

        Oak tree leaves provide food for the larvae of 534 species of butterflies and moths, more than any other tree.  And almost every one of those 534 species are food for baby birds.  It is estimated that an adult bird can eat 720 caterpillars a day.  And in addition to what the adults are eating, they must feed their nestlings every few minutes all day long.  That’s a lot of caterpillars!  In case you were wondering, next on the caterpillar host tree list is a tie between willow, cherry and plum which each support 456 caterpillar species.

        Besides the 534 caterpillar species, many other insects and squirrels, chipmunks, raccoons, deer, bears, mice, turkeys, grouse, wood ducks and other birds depend on oak trees to survive.  Along with the leaves, the acorns also provide food, and cavities provide nesting for dozens of bird species including chickadees, woodpeckers, flickers, owls, bluebirds and others.

        So why aren’t people planting more oaks?  The main reason is probably that they are relatively slow growing.  But so what?  They are the easiest of all the trees to plant, because you don’t have to lug a heavy tree home from the nursery, dig a big hole, heave the tree into the hole, and deal with all the other issues attendant with planting a tree, along with the expense of the tree itself.

        No, all you have to do is plant an acorn.  Place it on its side in a mostly sunny spot, about 1 ½ times as deep in the soil as the diameter of the acorn.  For example, if the acorn is an inch wide, plant it 1 ½ inches deep.  Protect the acorn from squirrels and mice by laying a piece of chicken wire over it before covering it with soil.  Water it well and wait.  A white oak acorn will germinate the same fall it is planted while red oaks acorns wait to germinate until the following spring.  For the first year, place a chicken wire cage around and over the seedling to protect it from animals.

        Young oaks may be carefully transplanted, but it’s best just to decide where you want it to grow for the next several hundred years and plant the acorn in that spot.  Why not plant an oak to commemorate the birth of a child or grandchild, or to mark the occasion of a wedding or other special event?  Generations to follow can visit the mighty oak and recall stories of family long gone who cared enough to plant an oak.


        While most of us don’t own enough acres to help restore the oak savanna, many stately old oaks still grace our cities and rural areas and we should do everything we can to protect and preserve them.

        The Wisconsin DNR advises us to protect oak trees from a fungal disease called oak wilt by not pruning oaks from April through October or any time the temperature is above 50°.  Oak wilt is a fatal disease that affects oaks in the red oak group – those with pointy leaf edges – most easily.  Oaks in the white oak group – those with rounded leaf edges – are less susceptible but can be infected.  The map  ________ shows where oak wilt has been found in Wisconsin.

        What the oak wilt fungus does is it blocks the pathways inside the tree where water moves.  When water can’t reach the tree top, the leaves wilt and drop off and the tree dies.          

        The disease spreads several ways. 

        Pruning or any tree damage that exposes live tree tissue can attract beetles that carry oak wilt disease spores within just 15 minutes!  Tree paint and wound dressing are no longer recommended for most pruning cuts or wounded tree surfaces, but if your oak tree is damaged or you are forced to prune between April and October, an immediate light painting of the cut or wound will help protect against oak wilt.  Take note:  immediate means right away.  Cut.  Paint.  It doesn’t mean make the cut and then go look for the paint, or take a break, or cut five other branches first.  Cut.  Paint.

        Where do these beetles get the disease to start with?  They are attracted to the sweet smell of fungal mats growing under the bark of oaks that have already died of oak wilt.  The mats grow and force the bark to crack open and the beetles swarm to feed on the sap.  The fungus gets on their bodies as they feed.  When a healthy oak has a fresh wound, they flock to the sap flowing from that tree and spread the fungal spores.

        Once a tree is infected with the fungus, the disease can also spread to nearby oaks whose roots have become interconnected underground.

        Another way the disease spreads is by moving contaminated firewood logs.  It is difficult to tell whether firewood is contaminated just by looking at it.  Fungal mats may be hiding under the bark.  So just don’t transport oak wood.

        The DNR website has much more information regarding determining whether your oak has wilt, what to do if it does, how to prevent the below ground spread to nearby oaks, and safely harvesting the wood of an infected tree.  Please see   Additional information can be found at

        The second major threat to our oaks is disturbance in the root zone.  An oak sends down a deep tap root to anchor its massive weight in place, but most of its hundreds of miles of roots are found in the upper 18 inches of soil and can reach four to seven times the width of the tree’s crown.  Any disturbance in the root zone, including trenching, covering with asphalt or concrete, inadequate drainage caused by installation of concrete foundations or pavement downhill from the tree, or even building up the soil around the tree by just an inch, can severely cripple an oak, eventually causing death.


        Yes, acorns are edible but eaten raw they are bitter tasting and can be toxic if consumed in large quantities.  However, they can be leached of their bitterness, which is caused by tannins, by boiling them in several changes of water until the water no longer turns brown.  After leaching there is a wide variety of culinary uses for acorns.  They can be roasted and used as a basis for a coffee-like drink, coarsely ground and used like nuts in any recipe, tossed with salad greens or potato salad, made into nut butter, and even pickled.  For expert detailed instructions for leaching and eating acorns, the book Nature’s Garden by Samuel Thayer is excellent.


        Anyone who has lived with an oak tree knows that some years the acorns fall in amounts large enough to necessitate removal with a backhoe, while in other years, only a few are produced.  The bumper crop years are called mast years.  Mast years seem to occur randomly and that is indeed the case.  Why does this happen?  It’s all part of the oak’s survival scheme.

        If an oak produced the same amount of acorns every year, they would support the same amount of animals every year and every acorn would be eaten, leaving none for growing new oak trees.  So they produce less in some years, causing the population of squirrels, chipmunks and others who love acorns to take a nose dive.  Then when the animal population is down, the oak will have a mast year.  The squirrels and chipmunks that do survive the lean years can’t possibly eat all that is produced in a mast year, so they bury the excess acorns hoping to come back later to retrieve them.  Some of those buried acorns are forgotten and those are the ones that the future of the species depends upon.

        You might be wondering how an oak tree “knows” when to have a mast year and when to have a lean year.  It doesn’t actually.  It happens randomly depending upon the weather at the time when their flowers need pollinating.  The flowers come out so early in spring that they risk a chance for frost or wet weather that deters pollination.  If pollination isn’t successful, very few or no acorns are produced.  If the weather is good and pollination is successful, a surfeit of acorns are produced.  In this way, mast years happen randomly, keeping the acorn eating animals on their toes and guaranteeing the propagation of the oak species.

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