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.
No Turtle Necks
One important rule of green thumb is not to pile mulch up around the necks or stems of your plants. A turtle neck or cone of mulch surrounding and touching the bark of trees, shrubs, and perennials can trap too much moisture on the bark and encourage disease problems. Keep the mulch 4 inches from tree trunks and 1 to 2 inches away from the stems of shrubs and perennials. You can feather the mulch so that a very light layer is sitting on top of the soil near the stems of plants with the thickness of the mulch getting deeper as you work your way away from the plants.
How Deep to Mulch
Although even a one inch layer of mulch will offer benefits to your plants the insulating properties of the mulch are best if it is put down at least 2 to 4 inches deep. A lightweight mulch of shredded leaves can be piled up to six inches deep or more. The shredded leaves will break down quickly so a leafy layer will often shrink to half of its original depth by the time spring arrives. In very cold winter areas a mulch that is 6 to 12 inch deep can help marginally hardy plants survive the cold. A loose or more chunky mulch of corn cobs, straw, or wood chips creates even better insulation because of the air pockets formed by the coarse mulching material.
Removing Mulch in Spring
A thick blanket of mulch acts as insulation from the cold, so when the sun comes out in the spring, it is possible for the soil to heat up quickly. This can cause the plants to break dormancy too soon. For this reason it is recommended that you pull a thick layer of mulch away from plants in early spring just as their buds begin to swell. The cooler soil temperatures caused by the removal of the mulch will stop the plants from leafing out too soon – before winter is really over.
Roses are especially happy to get a layer of mulch around their roots in the fall but wait until a first frost has hit to layer on more than six inches of mulch. This way the rose plants can “feel” the cold of the first frost and slide into a winter dormant state in late fall. Once a rose plant has gone dormant, the mulch will protect them from the heaving and thawing action of the soil in winter. Rose plants are often damaged when frozen soil begins to thaw and crack. If the soil is left bare, the freezing and thawing can push plant roots right out of the soil. Winter mulch around your rose plants can save their lives.
More Mulch, Less Mud
There is one more reason to give your garden the gift of mulch this fall: less mud. A covering of mulch on top of the soil will absorb excess water. A mulch will not only make your garden look better as it sleeps through winter, but with less mud being tracked indoors the inside of your home will benefit as well.
By Marianne Binetti | October 8, 2019