Mulch Your Organic Garden with Falling Leaves

Each fall, the leaves of deciduous trees and shrubs lose their green color and fall to the ground. This annual event is one of the preparations the tree is making to survive winter. Winter plant survival in the wild is aided by the build-up of fallen leaves, fallen needles, and other detritus that builds up on the forest floor. You can provide this same protection to your garden using fallen leaves to mulch vegetables, flowers, trees, and shrubs.

Freezing Air and Soil May Kill Plants

In northern gardens, the biggest winter threat to plants is freezing. Herbaceous plants and shrubs -those that die back to their roots each winter – are protected from frozen branches, but their roots are not protected from frozen soil.

If the air temperature where you garden sinks below freezing for even a few days during the winter, the top few inches of soil may also freeze. In the most northern gardens, the soil may freeze in early winter and stay frozen until spring.

The biggest danger to plants is soil that freezes and thaws and freezes again. This freeze-thaw cycle can push roots out of the ground, where they are subjected to air cold enough to kill them.

To prevent the freeze-thaw cycle from damaging your plants, you need to insulate the soil.

Protect Plants with Leaf Mulch

The best protection against frozen soil is mulch. A layer of mulch helps the ground maintain a more even temperature, even as the air temperature gets lower and lower. Mulching can prevent the freeze-thaw cycle from affecting plants in climates where winter freezing is sporadic.

All of those leaves piling up in your yard and on the sidewalk are a great source of mulch. You still have to rake them up, but once you do, don’t put them on the curb for the city to take away. Use them to blanket your garden.

Note: If the leaves have been treated with any pesticide, fungicide, or herbicide that is not organic, let the city have them. Also, do not use leaves from allelopathic trees, such as Black Walnut. The chemicals in allelopathic plants are toxic to most other plants.

Lay Leaf Mulch After First Heavy Frost

The time to mulch for winter protection is just after the first heavy frost. If the leaves fall several weeks before the first heavy frost, you can compost them in piles without other refuse to create “leaf mold.”

Leaf mold is partly decomposed leaves that are used as a soil amendment. If you mulch with leaf mold, in spring it will continue to decompose and work its way into your soil.

Leaves decompose faster if you shred them. Large leaves such as sugar maple, oak, and others must be shredded, even if you are not making leaf mold. These large leaves can create an impenetrable barrier on top of soil, preventing water from getting through to plants.

You can learn how to make leaf mold at Making Mulch From Leaves.

How Much Mulch to Use

In the flower garden, small leaves – 1-2 inches wide – can be used immediately. Pick up a rake full and place 1-2 inches of the leaves on any exposed soil in your flower garden. Do not snuggle the leaves up against the base of the plant as this can cause rot or provide an easy path for disease to enter the plant.

In the vegetable garden, root crops you want to continue harvesting during winter need heavy mulching to keep the soil loose for harvesting, as well as to prevent soil heave as a result of the freeze-thaw cycle. With root crops, you can pile the mulch directly above the plants if their leaves have already died back.

Cold hardy crops, such as kale, mustard, and cabbage, often taste better after a frost, but you still must prevent frozen roots to keep the entire plant alive. Using row cover to protect these plants from freezing air and laying a 2-3 inch layer of leaves or leaf mold on the soil should see them through until spring.