Are birch trees dropping more bio-bits on Anchorage this year?

Like everyone else, I complain about the all the detritus that falls from cottonwood trees every year. Who doesn’t? We got rid of almost all of those growing on our property and yet each summer there is cotton all over. I always marvel that our door mats become full of tiny germinating cottonwood trees.

This year I find myself starting to complain about all the birch detritus. Birch. Really! I never thought I would put these trees in the same category as cottonwood. After all, who doesn’t love birch trees?

Before you send emails supporting these wonderful hardwoods, know that I’m not suggesting that you get rid of birch, as I often do for cottonwoods. I am just ranting a bit as it seems to me this summer we have a lot more of those tiny, one-eighth-inch, beige bits and they are covering walkways, porches, the driveway, the cars parked outside — everything.

I didn’t give this deluge of birch junk much thought at first. I don’t really remember experiencing it before. However, I have been parking outdoors this summer and have been struck by the tremendous amount of the “stuff” on the car. No matter how often I clean it off, more appears within hours. It piqued my curiosity.

So, here is the scoop, I think. In the scientific terms there are two types of these tiny bits of organic matter. They are known as “samaras” and “scales.” The scales are the shape of a three-toed mouse or, for those into the French, fleurs-de-lis.

The samaras, on the other hand are more often referred to as nutlets or fruits. They are equally diminutive, but round or slightly heart-shaped and contain the seed.

I am ashamed to admit that I am so fixated on the size of birch leaves in the spring, waiting for them to get large enough to signal the end of frosts, that I pay little to no attention to the tiny flowers that form as the leaf buds open. These are female birch flowers, female catkins.


On the same branches, and equally under my radar in the spring, are male flowers. These catkins form in the fall and winter, releasing pollen once the female flowers are ready. I don’t have allergies, so again, this pretty much passed me, unnoticed.

Turns out, catkins eventually come apart, releasing fruits and scales to the wind. And now you know what you have been tracking into your house for the last couple of weeks and why there are so many birds — chickadees, sparrows and pine siskin — on the ground and what they have been eating.

All seeds rely on some sort of vector to disperse seeds. It turns out both cottonwoods and birch rely on wind to do the job. This is known as anemochory. You can only imagine how far some of these seeds traveled in last weekend’s big winds, but birch seeds usually really don’t travel too far, which is why you see expanding clumps of birch.

As long as I am this deep into the proverbial weeds, cottonwood produce fluffy seeds that get caught up in the wind. With birch, the seed isn’t the vehicle, the fruit is.

It is possible to start your own birch seedlings if you want. Gather some seed and place them on a damp paper towel. Stratification is really not needed, but it seems to help, so put the damp, seeded towel in a plastic locking bag in the fridge for three months. Then plant the whole towel in a container, covering the seed with a tiny bit of fine compost.

Or you skip the fridge, plant some seeds in a flat of compost and store the container outdoors for the winter. In the spring, birch seedlings should appear.

I still have questions about all of this detritus. Is there more this year? Is the timing different and should this have happened in early winter? An why didn’t last weekend’s “atmospheric river” winds do a better job clearing all the birch fruit and scales from my car?

Jeff’s Alaska Garden Calendar:

Alaska Botanical Garden: Beer in the Garden, Sept. 7 from 6-9 p.m. Beers and ciders and local foods in the fundraiser for The Garden. Learn more and and purchase tickets at

Don’t rake or blow, mow: All the stuff blown down on the lawn is great microbe food. Run it over with your mower if it isn’t too big.

Harvest: You know what ripe fruits and vegetables look like. Harvest yours when stuff is ready. Don’t wait for the end of the season.

Jeff Lowenfels

Jeff Lowenfels has written a weekly gardening column for the ADN for more than 45 years. His columns won the 2022 gold medal at the Garden Communicators International conference. He is the author of a series of books on organic gardening available at Amazon and elsewhere. He co-hosts the "Teaming With Microbes" podcast.