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A Warning When Using Fallen Leaves As Mulch

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Fall, with its crisp, cool air, brings beautiful color to deciduous trees—and, eventually, the land itself, as those beautiful leaves flutter down and pile up. Happily, fallen leaves can find new life within our gardens, with some key preparation first. 

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Fallen leaves are great for using as natural mulch. Not only will they save you the expense of purchasing mulch, but they will also help to enrich your soil, retain moisture and protect your plants from winter's fluctuating temperatures.

Here's the key thing, though: When using leaves as a mulch, consider shredding them first with a mulching mower, shredder or leaf blower on the vacuum setting. A light layer of leaves applied without being shredded can be fine, but a layer of whole leaves more than a few inches thick can block air and water from penetrating the ground. Thick layers of leaves can also do the exact opposite—locking in too much moisture, potentially damaging any plants that are susceptible to rot and other fungal diseases. Lastly, deep leaf cover can appeal to timid wildlife like mice and voles, because it allows them to tunnel; for this reason pull leaves back from the base of shrubs and young trees that are prone to these critters' gnawing.

When deciding whether to shred the leaves, it can help to consider what you are growing and what kind of natural setting it has evolved in, along with the ultimate depth of the layer. For instance, woodland species will be more successful under whole-leaf litter than plants from the open prairie. Leaves that land naturally in the garden might be shallow enough to keep whole, but adding all the leaves that fell on the lawn and paved areas might result in too thick a layer. A leaf layer that blocks light and traps water on the surface of a lawn will kill it.

Be aware that shredding leaves can destroy insects that use leaf litter for cover or incubation. To protect against this, you might choose to "leave the leaves." If the layer seems too deep or problematic for the specific plants in your garden, you might shred some leaves to reduce the volume and keep the rest whole, or redistribute whole leaves to certain areas of your property (if space allows). Both shredded and whole leaves will provide insulation for insects that hibernate below ground. 

Leaves can also be added to your compost bin (shredding is important here to speed their breakdown), contained for spring mulching or disposed of according to local regulations. You can also use a mulching mower to chop up a thin layer to be left on your lawn as a nitrogen-rich fertilizer. Read more about that here.