Wednesday, October 21, 2009


Acorns, the hard-shelled fruits of oak trees, are falling to the forest floor. Red oak, the most common oak in our region, is having a banner year. Their nuts are so thick on some sidewalks and woodland trails, it feels like walking on a bed of marbles.

Northern red oak acorns (Quercus rubra)

If only these were a great snack for humans, then I would not have to carry lunch in the field. Alas, the red oak acorns are full of tannins, which are not good for our digestion. One can make acorn flour, after a lengthy process of grinding and then rinsing in many changes of water.

Squirrels, mice, blue jays, rose-breasted grosbeaks, wood ducks, deer, wild turkeys, and other animals are a bit more fortunate. They can eat these nuts, although they do prefer white oak acorns, which have much less tannin.

Oaks fall into the "red oak" group and the "white oak" group. Leaves of the red oak group have pointed lobes, their acorns are bitter and mature in two years. White oak leaves have rounded lobes, their acorns mature in one year and are sweeter.

White oak leaf (left); Red oak leaf (right)

Acorns have a cap at the stem end. The caps of reds and whites are also different. The red oak has a flat saucer-shaped cap, looks like they are wearing a tam o'shanter. The white oaks, in contrast, sport a deeper tea-cup shaped cap that covers more of the nut.

The cap, more scientifically called a cupule or involucre, are the woody bracts that form around the ovary of the female oak flowers. A more fanciful name for these dime-sized caps is wee folk hat.

Red oak acorns

Oaks produce banner acorn crops only every 2-5 years for red oaks and 4-10 years for white oaks. Some years the trees produce only a few acorns. In average years a single tree may produce 10,000 acorns. A banner year may produce 100,000 acorns per tree. The amazing thing about these boom and bust acorn cycles is that it is a group phenomenon. Oaks synchronize the timing and quantity of acorn production. For example, all the red oaks in an area will have similar acorn crops in a given year.

Acorns are favorite foods of birds, mammals, and insects. Out of 10,000 acorns that fall from a single tree, likely only one will survive to germinate. More than 90% of the acorns that fall are eaten or damaged by predators.

This banner acorn crop will be a boon for all the animals that eat the nuts. Next year look for more mice and squirrels, which leads to a boost in hawk and owl populations. Deer populations will increase after fattening up on acorns in the fall. More mice and deer also means more ticks and Lyme disease. The white-footed mouse is a primary carrier of the Lyme disease spirochete (bacteria). Ticks become infected by feeding on mice (and other small mammals such as chipmunks). The ticks then hop onto deer (which are not a carrier of Lyme), which then move the infected ticks from place to place. Another reason not to feed or otherwise attract deer to your yard.

Oaks do not start to produce acorns until about age 20, and then only really good crops at age 50 and thereafter. Big oaks, with diameters of two-feet or more, produce healthy acorn crops. Clearing competing trees from under the canopy of maturing oaks is one way to enhance acorn production. This allows the oak to produce a broad canopy and lots of acorns.

Look for fallen acorns as you walk the woods this fall. Many acorns are now hidden beneath a bed of fallen leaves. Search for white and red oaks and notice the different leaves and acorns.


  1. Always love to read about oaks Ellen. They're my favorite type of tree, and I think my wife's as well, though the beech does run an extremely close second. Then there are the hornbeams to consider and then there are...............

  2. Hi,
    I'm writing a post about acorns also, please visit me at and wondered if I could use your acorn photo and, of course, put your name beneath it for credit and then send my visitors to your blog for your wonderful acorn info. My post is going to focus on my friend's complaint: "there are too many acorns on my driveway, blah, blah, blah. My response will be good natured but mention what a boon it is for many reasons.

    Let me know if I can use your photo and link to you...if not, no worries. I just found your blog. It's great!


  3. Hi Marnie,

    Yes, you are more than welcome to use my photo. Let me know if you want me to email a jpg or if you can grab it from the blog.

    I'll check out your blog - nice to meet you.