We love our trees. All summer they absorb sunlight, carbon dioxide, and nutrients from the soil and turn them into new green leaves that shade us on hot days, keep moisture in the air and soil, and harbour a huge number of living organisms.
As the days get shorter and cooler, all those leaves will soon become a liability. They can no longer photosynthesize as the temperature drops, but they still lose water, especially when it’s windy. No problem. Deciduous trees in our part of the world have adapted to winter by sending some of the nutrients from their leaves back down into the roots for storage. That’s why they turn colour, by the way – chlorophyll components break down, revealing the previously masked oranges, yellows, and reds of other chemicals.
Once it’s saved everything it can, the tree simply lets go of the leaves and they fall to the ground. There they provide shelter for overwintering insects, including butterfly larvae and other future pollinators, toads, fungi, and all the micro-organisms whose job it is to break down the leaves and return nutrients to the soil for use next year. A perfect circle!
In forests, leaf debris builds up over the years forming a rich layer of moist organic material, just perfect for growing woodland wildflowers. In addition to zillions of tiny creatures, that layer also supports a huge diversity of fungi that create an underground network, linking the trees and helping them access and share nutrients and water. Recent evidence also shows this system can even warn trees that pest species are about to invade.
But, our neighbourhood is not a forest, and falling leaves don’t always land in convenient places. Our yards may include gardens, lawns, paths, and driveways. If you must rake leaves away from these areas, here are some choices.
Rake leaves off your lawn or driveway onto your garden beds and spread them between your plants. If you can let the leaves dry for a day or two before raking, they’ll break up, leaving some bits to fertilize your lawn. Dry leaves also won’t form a mat over your garden plants. Exception: walnut leaves contain juglones, which kill many plants, so don’t put those on your garden. Upside: they also kill weeds, such as Dog-strangling Vine (DSV).
Pile leaves in a corner of your yard or in an open bin, and next spring, when they’ve started to break down, spread them on your garden. A layer of leaf mulch will retain water, enrich your soil, and inhibit weeds. At the Fletcher Wildlife Garden, where you would think there were plenty of leaves, we receive even more each fall from a local landscaper and use them for mulch and weed suppression the following spring.
If you really have no room to keep your leaves, please put them into a yard waste bag (or several) and bring them to Brewer Pond. No garden debris please! We can use your leaves to enrich the soil in the butterfly meadow and also to control DSV. If you’d like to do this, please email me (envirocrewOOS@gmail.com) to discuss when, where, how.
An Algonquin horticulture professor once referred to fall leaves as “gardeners’ gold.” Don't throw away your riches. Spend them on the environment in your own backyard!
Originally featured in the October 2020 OSCAR.