Backyard Nature: Where is all that pollen coming from? And why is there so much?

by Marjorie Rachlin

Sneezing? Itchy throat? Runny nose? The oak trees of Forest Hills and greater DC are shedding their pollen. Their yellow dust is everywhere, and allergies are kicking up.

Oak trees belong to a group of trees that have male flowers and female flowers on the same tree. The female flowers are so tiny (1/4 inch) you can barely see them. The male flowers are those pretty “catkins” you see hanging from the twigs right now. On each tree you will see hundreds of these little catkins, looking like decorators’ tassels. These produce the pollen.

Riding the wind

How does the pollen from one oak get to the female flower of another? Oaks depend on the wind, not insects or bees. They are one of a group of plants that are wind-pollinated: pine trees, grasses, ragweed, even corn (think of all those tassels).

Pollen is light and not sticky so when the wind blows it spreads the pollen everywhere. Hopefully one grain will land on a female flower.

We can expect a lot of pollen for the next two or three weeks. In our neighborhood, most of the wind-pollinated trees (willows, birches, hickories, walnuts) have already shed their pollen. The oaks come later. There are two main kinds of oaks in our area and usually the black oaks begin and the white oaks follow.

This photo shows a catkin from one of our local black oaks. Each of those little bumps is a male flower, filled with hundreds of pollen grains. They ripen over a period of a week or so. As they ripen, and the wind blows, you can imagine how much pollen that tree sends into the air.

Hit-and-miss… mostly miss

Wind pollination is a hit-and-miss affair, very inefficient. Will some pollen grain floating here and there land on a flower’s stigma? It’s chancy. That’s why plants relying on it must put forth huge amounts of pollen.

Fertilization occurs when a pollen grain (male) falls onto the flower’s stigma. Then the female flower begins the long process of growth that leads to the acorn.

Oak tree allergies are only the beginning

No one knows why some people are allergic to something and others are not. In some people, the oak pollen that gets into the eyes or respiratory system triggers a response from the immune system that brings the well-known symptoms.

The oak problem will pass, but some unfortunate people can expect trouble soon from the grasses. They are wind-pollinated also. We keep our lawns cut close, but a trip to the park or the country may bring the usual symptoms. The other main offender is ragweed, which causes “hay fever” in late summer.

A thought as you reach for the box of tissues

Nature’s processes are indeed a wonder, but sometimes they are inconvenient. Look on the bright side – without pollen there would be no acorns. We would not have a lot of little oak trees coming up to replace the old ones. Our squirrels, chipmunks and birds would go hungry. Hawks, foxes and other animals that eat the squirrels would go hungry. And so on up the food chain.

Knowing the purpose of even the smallest grain of pollen won’t cure your sniffles. But it may make you feel better about your seasonal suffering.