Leaf mold benefits soil structure and water retention

November 18, 2020

It is autumn and things are changing fast. Every fall, some birds' brains grow bigger. The black-capped chickadee’s hippocampus grows 30 percent larger. This means they can remember where they found seeds before.

Humans change too during autumn, producing the highest testosterone levels in men and women for the year. This is probably from the traditional fall mating of mammals. By mating in the fall, the babies are born in early spring when food is becoming more plentiful.

Babies born in autumn are more likely to live to 100 than babies born any other time of the year.

But most of all, fall is just that: the falling of leaves. Because of colder temperatures and less sunlight, leaves stop making chlorophyll, the green pigment that lets plants convert sunshine. Once the green fades, the other colors are revealed, such as bright-red anthocyanin, and yellow and orange carotenoids.

You can of course, compost the leaves, but there is something else you can use the leaves for in the garden. It is called “leaf mold” and is made by letting leaves break down and decompose over time. Leaf mold is crumbly, dark brown, almost black with a deep, earthy aroma.

Leaf mold is simply compost made from just leaves. Compost is great for improving the texture of your soil. Compost is also a good fertilizer. Leaf mold is more of a soil amendment. In fact, leaf mold doesn't really offer very many nutrients but conditions the soil. This means that the soil retains water better, often over 50 percent better water retention than soil without leaf mold.

By improving soil structure, it also encourages beneficial bacteria and home to earthworms.

It is easy to make leaf mold. Because leaves are pretty much all carbon, they break down slower than nitrogen-rich materials such as kitchen scraps and grass. It takes leaves anywhere from six months to a full year to break down into leaf mold.

One easy way to make leaf mold is simply raking leaves into big piles and leaving them to slowly break down on their own. Your leaf pile will work best if it is at least three feet wide and tall. Once in a while check the leaves, and if needed, hose down the pile, especially if there is no rain.

You can also put leaves into big plastic garbage bags. Stuff the bags with leaves, spray them to get them moist and cut some holes in the bag so air can get in and out.

To get the leaves to break down faster, cut them up by running a lawnmower over them. These smaller pieces decompose faster.

Turn the pile of leaves with a garden fork every few weeks. For leaves in a bag, just shake the bag to mix up the leaves. Both of these methods bring fresh air into the pile of leaves, causing them to break down quicker.

Besides doing duty in the garden, leaf mold is an excellent additive to potting soil or container plants, where its ability to retain water means less frequent watering and healthier plants.

So do not curse the ankle-deep leaves of autumn, but gather them and make one of the best soil amendments, leaf mold. Even if your brain's hippocampus doesn't grow like a chickadee’s you should still be able to remember to make leaf mold.

  • Paul Barbano writes about gardening from his home in Rehoboth Beach. Contact him by writing to P. O. Box 213, Lewes, DE 19958.

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