It won’t be long before you’ll get up one morning, look out the window, and exclaim: “Spring is finally here, the trees are starting to leaf-out.” Well, not so fast! They’re actually flowering. Leafing-out will come later.
We usually think of flowers as bright aromatic structures: Their color and aroma attracting the all important pollinators. What seldom attracts our attention are the small dull flowers of wind pollinated species, which includes most of our deciduous trees. As any North Dakotan knows, you don’t need bright showy flowers to attract the wind.
Elm, ash, oak, cottonwood, aspen, willow, and most all other deciduous trees produce flowers that are wind pollinated. Obvious exceptions include apple, hawthorn, and some other fruit-bearing trees.
Most of these wind pollinated flowers are produced in clusters, with each flower being small and drab. They typically have long exposed stamens and feathery stigmas to release and catch the pollen in the wind. They’re actually pretty neat. If all goes well, the next generation will be on its way.
If the trees leafed out first, the leaves would block the wind and few flowers would be pollinated. Because most of these flowers are produced high up in the tree on young twigs, we often incorrectly think that the tree is budding out. “Flower first; then leaf-out!”
You might be surprised to learn that many of our deciduous trees are either male trees or female trees. A plant will either produce male or female flowers: not both. Examples are green ash, willow, aspen, and cottonwood. You’ve probably noticed that some cottonwoods always produce cotton while others never do. Only female trees produce cotton. That’s their seeds being dispersed.
Now when you look out to see your trees “leafing out” you’ll know what’s really going on up there!