Wednesday 17th of April 2024

There is a movement to "leave the leaves" in gardens and on lawns. Should you do it?

If you haven't been living under a pile of leaves, you've undoubtedly heard of the "Leave the Leaves" movement, which has been gaining popularity in recent years.

The idea is not to send collected fallen leaves in bags to the landfill. Instead, we are encouraged to leave them be, allowing them to naturally decompose over the winter, enriching the soil with valuable organic matter, which also provides cover for dormant pollinators and other beneficial insects.

If done thoughtfully, leaving the leaves is one of the best ways to turn yard waste into free fertilizer, benefiting your plants, the environment, and your wallet. However, it's important to consider the types of leaves you're dealing with and where they land.

Leaving whole leaves on pathways where they can become slippery or on lawns where they can cause diseases should be avoided.

While lawn grasses can handle a light scattering of leaves, a thick layer can jeopardize their health. In snow-covered areas, moisture will be trapped between the lawns and leaves, leading to the growth of mold, fungi, and fungal infections. In snow-free regions, whole leaves are likely to smother the lawn and prevent moisture and sunlight from reaching the soil.

The solution that many have adopted is to mulch the leaves with a mulching mower and allow the fragments to fall between the grass blades, where they decompose, forming a rich soil conditioner. I myself recommended this approach before realizing that it could harm dormant insects and their larvae. We'll need these caterpillars (eventually moths and butterflies) and other pollinators in the spring, as well as newly hatched birds that depend entirely on insects for the first few weeks of life.

So what to do?

Currently, I rake (or blow) the leaves from my lawn onto the garden beds and spread them out to a depth of no more than 2 inches. To hasten decomposition, I sometimes add about an inch of homemade or store-bought compost on top of the leaves. No need to till it in; just leave it be.

The leaves usually break down significantly by spring and are nearly gone by summer. However, if they appear matted (again, conditions vary), remove them before spring growth resumes.

Leaves can also be used to create leaf mold—a type of compost made entirely from leaves. Simply pile them up in a corner of your yard, sprinkle them with nitrogen-rich fertilizers, and occasionally moisten the heap to prevent it from drying out. It may take a year or two, but the leaves will transform into a nutrient-rich soil conditioner that can be used as mulch or added to planting holes and containers.

Some leaves contain compounds that inhibit the growth of other plants. Black walnut is perhaps the most notorious, as the toxic chemical in its leaves called juglone negatively affects, and sometimes even kills, susceptible plants like Asian lilies, baptisia, hostas, hydrangeas, lilacs, petunias, apples, asparagus, cabbage, eggplants, peppers, tomatoes, and potatoes.

Avoid mulching beds with especially thick or broad leaves, such as those from oak trees, as their slow decomposition rate may block sunlight and water from reaching plant roots and, as a result, threaten their growth. However, they can be used in leaf mold piles if shredded, which is not ideal but better than sending them to the landfill and also avoids harming insects.

Fallen leaves are a natural mulch designed to protect (and fortify) the soil, insulate plant roots, and provide shelter for wildlife, as it happens in the forest floor. Why waste this valuable resource?