I’ve written and read lots about the importance of returning leaves to the earth where they will help develop friable soil with pore spaces for the exchange of oxygen and the drainage of water. Also, decomposing leaves contribute to plant nutrition and health. And further, a four-inch (10-cm) mulch of autumn leaves over exposed soil and around plants helps maintain moisture in the soil and prevent evaporation.
But foremost (and not so often cited), is that leaves are what worms eat, and worms are the most important inhabitants of good soil. A healthy population of worms in garden soil is comparable to the presence of cows in a pasture. They’re grazing on organic material and depositing nutrient-waste whenever the soil is unfrozen. Worms produce castings, a nutrient-rich waste that’s ideal food for plants. We need to remember that wherever our gardens are located, the land has been in use for no more than 300 years, at the most. Before that, worms provided the fertilizer, and it was sufficient to grow majestic forests. Of course, we will continue to fertilize our plants, but we mustn’t discount the nutritional importance of worm contributions.
The way to get a thriving worm population is the same way to get raccoons — feed them. Allowing fallen tree and shrub leaves to remain on the soil surface is a dinner invitation for worms. They feed mainly from dusk to dawn, and will extend from their burrows and feel around (because they’re blind) for any leaf material they can reach. If you sit on your doorstep after dark on a quiet night, you may hear a rustling of dried leaves on the ground — the sound of worms grasping leaves. If this is hard to believe, just try it.
I’m mentioning this before the leaves fall, just in case anyone in your household needs convincing to allow them to remain on bare soil. The urge to tidy up and collect fallen leaves is overwhelming for some people, and they need lots of reassuring support to change their housekeeping habits.