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The close of the growing season is one of the most beautiful times of year in the northwest. The sun typically sticks around for a while even as daytime air temperatures are cooling, resulting in foggy mornings and dewy spider webs. As day length decreases, deciduous trees and shrubs begin pulling starches and sugars out of their leaves and storing all of that energy in stems and roots for the next season. As this occurs, chlorophyll production slows and the resulting oranges, reds and yellows of the trace pigments and minerals that are left behind start to show off. Finally, the leaves fall to the ground where nature intends them to help create deeper, healthier soils as they decompose.

Urban Settings & Fall Leaves

If we move the setting from a native forest to an urban landscape appearance, safety concerns begin to impact this natural process. Our landscape contractors come in and rake, blow and vacuum leaves up, struggling against fall rains and a variety of tree species, some of which give their leaves up very grudgingly over a long period of time, in order that our landscapes should look manicured and free from “slip and fall” hazards. This is a work-intensive process often resulting in increased waste, transportation and fossil fuel usage. We are, in effect, breaking the natural cycle by collecting and removing the leaves thereby obstructing a natural process that is otherwise complete.

“Leaf Mulch”

While removing leaves from hard surfaces such as sidewalks and parking lots will remain a critical part of effective risk reduction and property management, aesthetic expectations are evolving in regards to the rest of the landscape. For evidence of this, type “leaf mulch” into your Internet browser. You’ll get pages of articles, research and success stories encouraging you to simply leave leaves be! This is not just a homeowner trend. Commercial and municipal property managers are finding greater acceptance for a different aesthetic from their tenants and communities who increasingly embrace sustainability.

Trees are very effective at sourcing mineral elements from the soil, some of which remain in leaves when they drop. Chief amongst these elements is carbon which balances nitrogen in the soil and provides a food source to many different decomposers vital to the nutrient cycle. As leaves break down they release a complex of acids, collectively called humic acid, that help form soil colloids, relieve compaction and aid in moisture retention. Further, leaves as a mulch on the surface will insulate the soil, protecting tender plants from the cold and help suppress weed seed germination.

How to Use Leaf Mulch in Your Community’s Landscaping

There are several ways to employ leaf mulch on your site in the fall. After leaves are blown off of hard surfaces your contractor can simply mow leaf-covered turf areas with a mulch mower, chopping leaves up and mixing them with grass clippings. This mixture will break down faster than leaves alone since the nitrogen in the grass clippings will excite more microbial activity. As with regular mulch mowing, care should be taken to avoid leaving large clumps on the surface that can smother underlying grass.

In beds, whole leaves can often be left in less visible areas such as under and around large shrub and tree plantings and in remote areas where aesthetics aren’t critical. In areas of higher visibility where this may not be acceptable, consider re-applying partially processed leaves that have been diced through a commercial leaf-vacuum. Another alternative may be on-site composting which can produce an even more refined product with the help of your contractor.

Whatever methods you and your contractor employ with your leaves this fall, stay focused on the ideal of closing the loop of the nutrient cycle and keep your leaves on site.