Fall is finally here, which means leaves are falling. This is nature’s way of protecting plants through the cold winter and improving soil each year. You can think of fallen leaves as the most natural autumn mulch. However, there are some tree leaves that can be toxic to soil pathogens when used as a mulch: avoid using back walnut leaves and those from any eucalyptus plant for mulching.
What is a Mulch?
A mulch is simply a covering that sits on top of the soil, acting like a blanket to insulate and as a barrier to protect from new weeds. A mulch will also trap moisture in the soil. In dry climates, rocks and gravel are used as a mulch, but mulching material that is made from organic sources such as leaves, bark chips, or compost will not only insulate, conserve water, and block weeds but improve the soil as well.
So can you just pile up old leaves on top of your plants for winter protection? Not so fast. Decaying leaves will improve the soil, block weeds, and protect plants from freezing, but in their natural fallen state they will also encourage burrowing rodents and fungal infections on the stems and trunks of plants due to poor air circulation. The best way to use fallen leaves is to mow or shred them before using.
Rake leaves onto grass or open area. Spread leaves apart so they will dry a bit then run over the leaves with your mower. Turn around and mow over the leaves a second time. Now, even large maple leaves will be ready to be raked up and spread on top of the soil around your favorite trees, shrubs, and perennials. Some gardeners use a leaf blower to return the newly mowed leaf bits to the garden bed.
If you don’t have a supply of fallen leaves to mow, you can purchase wood chips, bark chips, or compost to use as your autumn mulching material.