Harvesting Autumn Leaves

I can think of good reasons to rake autumn leaves into huge piles, none of which involves stuffing them into plastic bags left at curbside until trash day. Most important when she was younger was Lynne’s need to jump feet first from a running start into the pile, to hide perfectly still below the surface, breathing in the pungent organic odor, until routed out by the old dog’s cold nose. I am too old to fly into the pile as Lynne once did, but I have memory of being ten years old on blue-sky October afternoons, my father heaping up the leaves after every flying leap. And I can still wrestle in the leaves with Mia the Beagle.

Now I gather them in October to recycle their nutrients into compost, to use them as mulch for all the garden beds come spring, and to turn them into a rich organic soil amendment. True, much of what leaves contain at the end of their life is transferred to roots and stems before the leaf dies. But those dry, brown remnants of summer have a surprisingly high nutrient element analysis. Fallen leaves of deciduous trees such as maple, beech, ash, and oak contain about 0.5 percent nitrogen, 0.1 percent phosphorus, and 0.5 percent potassium along with equally substantial amounts of calcium and magnesium, all essential nutrients for plant growth. The needles of white pine, a common tree throughout much of New England, contain similar nutrient levels.

Many people believe that pine needles are too acidic to be recycled in the garden and thus overlook this abundant source of carbon. In fact, pine needles are no more acidic than oak leaves. If composted intact, they do tend to take a bit longer to break down due to their waxy coating. If shredded with the leaves of hardwoods, however, they decompose almost as quickly as shredded leaves.

Fallen leaves are mostly carbon and thus their decomposition is a slow process, their nutrients released gradually – nature’s version of a slow-release fertilizer. Indeed, annual topdressing with compost made from autumn leaves and fresh stable litter is all the fertilizer that trees, shrubs, and many perennials need for healthy growth. Even lawns are healthier for the nutrients released from fallen leaves by a mulching lawn mower.

Nutrients, however, are only part of the garden worth of autumn leaves. Leaf mold, a soil amendment produced by the fungal decomposition of damp leaves, will substantially improve both the structure and the water-holding capacity of soil. While rich topsoil can hold 60 percent of its weight in water (compared with 20 percent for subsoil), leaf mold can retain 300 percent or more of its weight in water.

The question then becomes not what to do with autumn leaves, but how to do it, how to harvest dry leaves for mulch and how to make leaf mold? Start by shredding the dry leaves into small pieces that will break down quickly. This can be done with special grinders designed for the task or with a lawn mower. I know one gardener who puts his dry leaves in a trash can and shreds them with a weed whacker.

Leaves collected for use as mulch during the next gardening season must be completely dry, crispy dry. If not, they will start to decompose during winter storage, turning into leaf mold. Should this happen, add the damp leaves to the compost pile. Dry shredded leaves can be added to the compost pile as well. Wet or dry, be sure to mix the leaves with high-nitrogen materials such as fresh grass clippings or fresh stable manure. Too many leaves will stall the composting process, but a mixture of two parts (by volume) leaves to one part grass clippings or manure will decompose quickly during the growing season.

An alternative to composting damp leaves is the production of leaf mold, a soil amendment that is far superior to compost for improving soil texture and water-holding capacity. In fact, producing leaf mold is a form of composting in which the leaves are the only ingredient. Simply place the leaves in a wire bin that is at least three feet wide and tall, thoroughly dampen the leaves, and monitor the moisture level to ensure the leaves remain damp, adding water as needed. Six to twelve months later, you should have a dark brown crumply product, much like compost, with a pleasant earthy smell.

You can begin the processes of composting and leaf mold production in October, but don’t expect to much progress until the following spring, after the piles thaw out. The finished products can be used in late summer and fall.

Reluctant to rob nutrients from the woodland garden, we harvest only the leaves that accumulate on the driveway, relying on willing neighbors for an endless supply of autumn leaves, hauling them home and spreading them out on the drain field to be shredded with the mower. The bulk of our dry shredded leaves are then packed into large plastic bags for storage until needed as mulch during the following garden season.

If, by chance, the shredded leaves you intended for storage get damp, you may be able to salvage them for winter storage by letting them dry on tarps in the sun. This year serves as a god example. With a 10-day vacation coming up, we had no choice but to start shredding the leaves in the driveway, even though they were slightly damp. We dumped the shredded leaves on tarps and plan to expose them to as much sunlight as possible, both before and after our vacation.

A word of caution to those who go begging for leaves: be sure that no insecticides or herbicides were used where the leaves are collected. Trees may accumulate these products in their leaves during the growing season and they may still be present after the leaves fall.

Autumn leaves are too valuable to be treated as trash or burned. If you are not able to recycle all the leaves that fall on the lawn in your own garden, find a gardener who will use them! And check with local government officials to see if your community operates a leaf pick-up and composting program for its residents.