​

Why do leaves kill grass but snow does not?

​
📓 The short answer

Leaves can kill grass if they pile up thickly, blocking light and airflow, but a light layer can fertilize and support soil health. Snow usually doesn’t hurt grass and may help it survive winter by insulating it and adding moisture and nutrients, though problems like snow mold can occur.

📚 The long lawn answer

In the fall season, a common sequence of events occurs:

• Step 1: Tree leaves change from green to oranges, reds, and yellows.
• Step 2: The leaves fall to the ground.
• Step 3: People dutifully rake, blow, and lawnmower the leaves off their lawns.

All this leaf-moving happens because it's common (though debated) gardening advice that removing piled up leaves can help protect your lawn. But if leaves supposedly kill grass, why doesn't snow?

As with most questions, the answer is not black and white. Both leaves and snow can kill grass, but not always. Here's why:

Do leaves kill grass?

Leaves can kill grass, but only if they're left to excessively pile up.

A thick mat of leaves where you can barely see the grass can block sunlight, trap moisture, and limit airflow. Like any plant, grass needs to photosynthesize and when piles of dead leaves smother it, it can die.

Heavy piles of leaves can also proliferate lawn diseases since mold and fungus can grow in these low-airflow and dark environments. It's recommended to keep leaf cover below about 20% of your lawn to avoid harming the grass.

But you should still leave some leaves on your lawn. The fallen leaves are free fertilizer for your grass, chock full of nitrogen, phosphorus, and potassium. When you let some decompose, it returns this organic matter to your lawn and can improve soil health.

And while not specifically related to grass health, it should be noted that dead leaves provide a habitat for insects, spiders, slugs, and small animals. So it can be environmentally friendly to leave your leaves, especially in places where grass is unlikely to grow anyways, like directly under a tree.

Does snow kill grass?

No, snow usually doesn't kill grass and can even help it survive the winter.

When winter rolls around and sunlight becomes less available, grass goes into a period of dormancy to conserve energy and survive the season. While heavy snow can block sunlight, it's not as much of an issue since the dormant grass is not relying on photosynthesis as much.

In fact, snow has several benefits that help dormant grass survive the winter.

• ✅ Snow protects grass from extreme cold: The main benefit is that snow can insulate the lawn and protect it from the harshest cold temperatures, especially harsh winds and repeated frost-thaw cycles.
  ​
• ✅ Snow provides nitrogen to grass: Snow can capture nitrogen from the air as it falls. When it melts, grass absorbs this fertilizing nutrient to give itself a boost for spring growth. Snow has even been called "poor man's fertilizer" for this reason.
  ​
• ✅ Snow adds moisture to grass: Grass can get water from the melting snow, which helps it survive, especially when cold winds would otherwise dry it out.

But there are also some ways that snow can harm grass. Here are some negative effects of snow on your lawn:

• ❌ Snow mold can kill grass: When snow gets piled up, it can create a damp environment leading to snow mold, a fungal lawn disease. As the snow melts away, patches of grass affected by the disease will be dead or bleached by snow mold.

• ❌ Walking on snow can kill grass: While tempting to walk on a snow-covered lawn, each footstep compacts the snow, which can make it harder for air and water to reach the roots of your grass. In the springtime, you may notice footprints of death* when the snow melts.

Overall, a moderate dusting of snow can be a good thing for your lawn. But if you're concerned for your lawn's winter health, then rake heavy piles of leaves before snow falls (which can be breeding grounds for snow mold), make sure your lawn has proper drainage, and avoid making snow angels if you can resist the temptation.

--- Thanks for reading this week's newsletter! If you have any thoughts, questions, or favorite GIFs, my inbox is always open. Just hit reply to send me a note! :) ​ All my best, Caitlin ​Click here to read five facts about Caitlin​

​

​Sources for this week's newsletter​

* I hereby call dibs on the band name "Footprints of Death."

🌐 Wikipedia article of the week

​Shower-curtain effect​

"The shower-curtain effect in physics describes the phenomenon of a shower curtain being blown inward when a shower is running. The problem of identifying the cause of this effect has been featured in Scientific American magazine, with several hypotheses given to explain the phenomenon but no definite conclusion."

​

📚 Did you know all affiliate revenue from book purchases is donated to charity? Today You Should Know is an affiliate for Bookshop, an online book marketplace that supports local, independent bookstores. I frequently update the Today You Should Know recommended reading list with my favorite fiction and nonfiction books. And I donate all affiliate proceeds to Room to Read, a leading nonprofit for children's literacy and girls' education across Asia and Africa. It's a win-win-win: you get to read a book, small bookstores get some business, and money is donated to a great cause. ​ Find your next read ​ 📕 Latest addition: White Trash: The 400-Year Untold History of Class in America by Nancy Isenberg

👀 Catch up on other curious questions

• ​Why do leaves change color in the fall?​​
• ​Can we build full-size buildings using LEGO-like bricks?​​
• ​Why do clean sheets feel so good?​​

P.S. 🤔 Do you have a question for the newsletter? Click here to submit your question (or reply to this email!)