In the fall, Margo Bates fills as many as 30 bags a week with fallen leaves from the towering oak trees in her yard in Baltimore’s Guilford neighborhood. Acorns make the bags so heavy that she rakes those down onto the street first, so that passing cars will run them over, before bagging their crushed remains, too. Otherwise, she said, “when the snow comes, and when you try to clean up your gardens to plant next year, you’re cleaning up wet leaves — yuck.” Tens of thousands of people across the Baltimore region take part each year in the annual ritual of raking their leaves into heaping piles, bagging them and sending them away before family members arrive for Thanksgiving and snow covers the ground over the winter. While tradition and peer pressure from neighbors can make keeping a leaf-free yard feel like an obligation, raking them all away is actually bad for the yards, bees and other insects, and the rest of the environment, experts say. “It’s good to leave as much leaf litter on the land as possible,” said Jon Traunfeld, director of the Home & Garden Information Center at the University of Maryland College of Agriculture and Natural Resources. “Leaves fall, and the nutr...