Leaf Mold is Gold
Fallen leaves make one of the best soil amendments around
Leaf mold—a type of organic matter, not a fungus—is what you get when leaves are partially or completely decomposed, explains Dawn Pettinelli, a soil scientist and assistant extension educator at the University of Connecticut, Storrs. You use it like compost, but it’s a lot less work, and you don’t need to worry about food scraps attracting critters. Just rake all your leaves into one area of your yard—ideally where it’s not an eyesore, and wind won’t undo your work—and leave them be. “Add to your pile every year in the fall,” Pettinelli says. “After a year or so, you’ll be able to remove leaf mold from the bottom of it every spring.”
Can’t wait? You can get leaf mold in as little as six months. “If you want leaf mold for next spring, get started early and aim for a pile that’s about four feet in every dimension,” says Pettinelli. “As the leaves decompose, it’ll start to shrink.” Shred the leaves first to give them a head start; add a source of nitrogen like alfalfa meal, manure, or blood meal, making sure the pile’s got adequate moisture, and turn it twice a month. “If you don’t turn it, you’ll get a hard crust on top so moisture and air can’t get in, and the leaves in the middle won’t get oxygen, slowing decomposition,” she adds.
Building a DIY bin is a snap. A cylinder of chicken wire, wood stakes, and heavy-duty staples are all you really need. “Hardware cloth is sturdy and long lasting, but it can make it harder to turn the pile,” says Pettinelli. That said, the easiest way to turn the leaves is to simply lift off the bin, set it to one side, then refill it, so the leaves that were on the top are on the bottom.
Leaves from a mix of tree species make better mold. “If you’ve only got one type, you’re limited in what organisms will help break it down,” Pettinelli says. Soft leaves from trees like maple, ash, and birch will attract bacteria. Tougher leaves, like oak, are great food for fungi. In addition to these microorganisms, insects like pill bugs, centipedes, and beetles are natural shredders who love a good leaf pile. “Whether you shred the leaves yourself or nature does it for you, finer particles will help hold moisture in and speed up decomposition.”
There are leaves you shouldn’t keep. Unlike composting, where temperatures within the pile can soar, making leaf mold is a cold process. That means you shouldn’t include any leaves from trees that have fungal diseases. “A hot compost could kill the spores, but in a leaf mold bin they will winter over and re-infect your trees in the spring,” Pettinelli explains. Black walnut is another to be careful with: These trees contain juglones, a natural herbicide. Though you could use leaf mold that included black walnut around trees and shrubs, don’t use it in flower or vegetable gardens.
Your garden will thank you. “Leaf mold is a great way to add organic matter to your garden without overfertilizing it,” says Pettinelli. Manure-based compost can have more nutrients than plants actually need, and the excess will leach into the soil. Decomposed leaves have fewer nutrients—most have been taken up by the tree—making them an ideal amendment to enhance soil’s permeability and water retention. All that, and they’re free.
Thanks to: Dawn Pettinelli, manager of the Soil Nutrient Analysis Laboratory and assistant extension educator, University of Connecticut, Storrs