October 20, 2018
Every fall, we experience a seasonal tree drama as leaves change color, die and fall. The leaves begin accumulating on our walkways, driveways, decks and gardens. This can provoke a dash for a rake or a leaf blower to corral, bag and remove the crunchy debris. This year, I encourage you to fight that urge. Let the deciduous tree leaves be. Rather than thinking of the leafy mounds as chore, reframe them as a gift from Mother Nature to you, your plants and your soil.
Leaf litter is nature’s mulch and soil builder. It’s free, it’s nutritious and did I mention it’s free? This natural mulch retards weeds and keeps precious moisture from evaporating. To appreciate the impact of leaves, it helps to understand the role, structure and nutrient requirements of soil.
Soil has many jobs in the garden. It provides support for the roots of plants and insulates them from temperature extremes. It’s a habitat for algae, bacteria, invertebrates and fungi that assist in decomposition and keep the soil aerated. Soil holds water, which hydrates and delivers nutrients to the plants.
In order to provide all these services to plants, the soil needs to be structured with enough pore space to drain sufficiently and maintain a healthy combination of water and oxygen. Pore space contains water, minerals, organic matter and the waste from microbes — a nutritious stew for healthy plants. This important pore space can be maintained by the introduction of organic matter in the mix. Organic matter includes decomposed living materials that brings us back to our leaves.
Leaving leaves on the ground for mulch allows them to decompose. Decomposition releases nitrogen that is converted by microbes into food for plants and animals. In the world of biogeochemistry, Mother Nature’s way of providing food is called nutrient cycling. The rate of this cycling changes as do the drivers of decomposition like the amount of moisture available and temperature.
Spreading a couple of inches of dead leaves around your garden protects the plants and soil through our cold, rainy season. Leaves have an insulating quality and keep the rain from bearing down directly on the soil, which can lead to soil compaction. If the soil is compacted, it loses those critical pore spaces and reduces the soil’s water and nutrient retention. As with most mulch, leaf litter also helps battle soil erosion as it protects areas with looser footing.
The warmth and moisture of leaf mulch attracts bugs and microbes that call our soil home. Leaf litter provides protection, nesting material and nutrients for the critters that help with the decomposition and aeration. Having all those animals in your garden increases biodiversity and the overall health of your garden. And don’t forget the birds. They love to flip a leaf over and discover their dinner.
Here are a few helpful tips if you decide to let nature take its course:
• If you have a diseased plant don’t use the leaves for mulch. The leaves of plants in the camellia/rhododendron/azalea family, as well as fuchsias and roses, may transmit pest or diseases to your plants in the next season. It’s always a good idea to remove debris from sick or dying plants as part of the integrated pest management.
• The smaller the litter, the faster it decomposes and more rainwater reaches the soil. Some folks mow or weed whack their leaves before spreading.
• You’ll want to rake the leaves away from the base of plants so they don’t make contact with the trunk or stem. Make sure the leaves aren’t smothering plants, too.
So give going natural a try this year. You’ll have to get used to the sight of brown leaves tucked here, there and everywhere. But in the spring, when your new upstarts push through moist crumbling soil, protected under a blanket of nourishing litter, you’ll never look at a pile of leaves the same way.