Leave the leaves this fall

Autumn is here! Although the fall season officially began more than two months ago, it finally feels as if it’s arrived. The cooler temperatures are invigorating and a welcome change, and rainstorms during the last two weeks have brought much-needed precipitation and relief from smoky skies.

Fall is one of my favorite times of year. We’re fortunate to have lots of beautiful deciduous trees in our county: ginkgo, liquidambar, Chinese pistache, Japanese maple, and more. When their leaves display peak fall color, the vibrant hues are like a celebration. The party only ceases when the colors fade and the leaves flutter to the ground.

And then begins the dilemma: what to do with all those fallen leaves?

Sadly, many homeowners still deal with the bounty of autumn leaves by collecting, bagging, and disposing of them. Leaves are treated as a nuisance or as trash to be hauled away to the landfill.

Fortunately, most municipalities are changing this practice by handling “green waste” separately from household trash and by implementing composting programs. In California, these actions were in large part driven by Assembly Bill 939 (AB 939), the 1989 law mandating that all cities and counties divert at least 50% of their waste stream from landfills. Despite laws such as these, the U.S. Environmental Protection Agency estimates that yard waste (leaves and other plant material) still amounts to roughly 13 percent of our country’s municipal solid waste!

Leaves are usually removed from most residential yards and commercial properties and taken to a collection facility of some type. Instead of moving your leaves offsite, there are many ecologically sound reasons to “leave the leaves” in your landscape:

  • Your trees invest a lot of time and energy producing all those nutrient-rich leaves, most of which can be allowed to remain where they drop in garden beds. They form organic mulch that retains soil moisture, suppresses weeds, improves soil health, and supports beneficial soil organisms.
  • On lawns, leaves can be chopped up using a mower with a sharp and specialized mulching blade. The resulting tiny leaf bits can be left in place along with grass clippings; they will settle into the lawn, decompose slowly, and act as a natural soil amendment. (Whole leaves should not be left on lawns.)
  • Allowing your leaves to remain where they fall saves a lot of time, effort, and even money (particularly if you pay for yard maintenance).
  • Fallen leaves help support a diverse ecosystem. Many birds, small mammals, lizards, and beneficial insects use dead leaves for nesting material, shelter, and food.

If you can’t keep your leaves in place for some reason, you can still collect them and use them on your property in other ways.

  • Large leaves can be cut into smaller pieces using a lawnmower or shredder and then redistributed as weed-suppressing mulch in the landscape.
  • Leaves can be used as the brown matter component in a compost bin. The finished compost can later be used to “top-dress” and enrich your soil.
  • Leaves can be piled on a patch of open soil. If kept moist, they will soon break down into “leaf mold” (partially decomposed leaves) that makes a rich soil amendment

Of course, there are some special considerations. Leaves from infested or diseased trees should be collected and disposed of to prevent spread of harmful organisms. Leaves from certain types of trees (walnuts and eucalyptus species, for example) can be allelopathic, which means they can harm other plants or inhibit their growth; these leaves should not be left in place.

Yet another reason for leaving the leaves is that large-scale leaf collection and removal can be detrimental. Consider these facts:

  • Leaves stuffed into plastic bags or other non-biodegradable containers can’t be commercially composted; they must be handled as trash, not as a reusable resource.
  • When placed in a typical landfill environment, organic leaf matter doesn’t receive enough oxygen to decompose properly. Instead, it produces methane gas, which is a greenhouse gas associated with climate change.
  • Most commercial-grade leaf blowers have polluting two-stroke gas engines, although cleaner four-stroke engines are being phased in. Research shows that a typical leaf blower operated for half an hour generates as many pollutants as a car driven for 50 to 400 miles! They are also noisy and sources of particulate pollution from blowing dust. (If a leaf blower or mower must be used, consider a quiet and non-polluting electric or battery-powered model.)
  • Vehicles used by municipal leaf removal services and commercial landscapers generate lots of air and noise pollution while collecting, transporting, and moving leaves.

Personally, when I need to collect or move my leaves, I still love my rake. It’s cheap, non-polluting, and quiet to operate, and using it is good exercise and an opportunity for some fresh air and peaceful time outdoors. It’s also a joy to get an up-close look at fall leaves with their different forms, ornate vein patterns, and hues of yellow, orange, and red.

This autumn, consider a different approach to your leaves. Leave them where they fall when possible, and when not, keep them on your property and treat them as the valuable resource they are.

If you’d like to try making compost, see these resources:


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