- Author: Cindy Kerson, UC Master Gardener of Napa County
Every year at this time, deciduous trees drop their leaves. This natural phenomenon has many benefits. For one thing, trees don't really need their leaves now that the days are shorter and there's less sunlight for photosynthesis.
Interestingly, leaf-dropping trees and plants are responding not to the loss of sunlight but to the increasing hours of darkness as the nights get longer. Leaves turn yellow, gold, copper, and orange because the tree is undergoing a phytohormonal process known as abscission. A layer develops between the leaf and the twig it's attached to, cutting off water and nutrients. In a sense, the leaves aren't falling; the trees are pushing them off.
Without their leaves, the trees can put their energy into root and structure growth and strength. They can retain more water and nutrients in these areas during the colder months.
Snow and rain could damage leaves if they remained on the tree. Without leaves, winter's cold air and wind can more easily pass through the branches, minimizing the fungal diseases associated with wet weather. On sunny days, sunlight and warmth can reach the ground under the tree.
If you have deciduous trees shading and cooling your home and yard in summer, you may appreciate the extra light and warmth that you get in winter after those trees lose their leaves.
We can get other important benefits from foliage drop if we let those leaves remain on the ground. First, they provide free organic mulch, better than anything you can buy. The leaves are compatible with the local ecosystem given that they originate here, unlike some storebought mulches made of bark from trees that may not even grow in our area.
Fallen leaves provide a haven for bugs and other microorganisms that appreciate that dark, moist environment. Beneficial spiders, gnats, overwintering butterflies and caterpillars, worms, moths, and bumblebees often take up residence in leaf mulch. Of course, less desirable critters—stink bugs, boxelder bugs, beetles, and roaches—enjoy that leafy habitat as well. We may dislike them, but they play a role in the ecosystem, and we should tolerate them (within reason, of course).
Leave those leaves on your lawn if you still have one. Lawns are no friend to the environment as they provide few nutrients to the local bugs and require too much water and too many chemicals to thrive. However, if you mow any fallen leaves right onto your lawn, they will provide a natural cover and nutrient layer that protects it during the colder and (hopefully) wetter months. Mowing will also reduce the leaf volume and prevent moisture buildup, which can harm a dormant lawn.
Some trees, plants, bushes, and hedges drop so many leaves that they may suffocate the plants under them. Fallen leaves can also harbor fungi or bacteria, and if you leave them near the roots or touching the trunks of a plant, they can promote disease. Better to move the leaves away from the trunk by hand, rake, or broom. You can toss them into your own compost pile or the city's brown compost bins, but don't put them in plastic bags in your garbage. That would be a waste of a beautiful natural resource.
My husband and I have a Raywood ash in our backyard that drops a tremendous number of leaves in the fall. We spread them in our vineyard.
If you want to view this phenomenon, come to the Las Flores Learning Gardens at the Las Flores Community Center in North Napa and you'll see more leaves than you can imagine. They blanket the low-water and native gardens until we can get around to cleaning them up. The leaves are so abundant that we have to order extra compost bins to have them carted away.
I know, I know. I just said, “don't remove them, move them,” but in this case, we have no place to move them to. At least by sending them to the community compost center, we know they will be properly utilized.
While it's customary to rake and dispose of autumn leaves, I encourage you to give that practice another thought. Leaves can look beautiful and natural in your garden if properly spread. And knowing that you're creating a winter habitat for important species is gratifying. You are doing your part to support the ecosystem.
Lastly, as the leaves decompose, they nourish the very plants that dropped them. Those grateful plants will use the gathered nutrients next spring for the big burst of life that we look forward to after a long winter.
Food Growing Forum:Join UC Master Gardeners of Napa County for a free workshop on “Favorite Food Plants” on Sunday, November 12, from 3 pm to 4 pm via Zoom. Master Gardeners will share the edible plants that they consider to be must-haves in their gardens. Get cultivation and harvest tips, too. Register Here to get the Zoom link.
Gardening Workshop: Join UC Master Gardeners of Napa County for a free workshop on “Gardening with the Masters” on Saturday, November 18, from 10 am to noon, at Ole Health Garden, 300 Hartle Court, Napa. Children five and older are welcome if accompanied by an adult. Class size is limited. Register to attend.
Help Desk: The Master Gardener Help Desk is available to answer your garden questions on Mondays and Fridays from 10 am until 1 pm at the University of California Cooperative Extension Office, 1710 Soscol Avenue, Suite 4, Napa. Or send your questions to firstname.lastname@example.org. Include your name, address, phone number and a brief description.