It’s that time of year again in New England. Leaves are everywhere!
When it comes to leaves, one man’s trash is most definitely another’s treasure!
Some nearby towns allow homeowners to put their bagged leaves out by the curb for pickup with the trash. Am I the only one with the urge to pull over and grab these bags of leaves for my compost pile? Fall leaves are one of a gardeners’ greatest resources, and most of them get thrown away!
Leaf mold is gardeners’ gold
Tree leaves are full of nutrients and trace minerals pulled from deep in the earth by tree roots. Recycle them back into your garden by piling them in a shady spot and letting them rot for a while. Broken-down leaves (leaf mold) make an excellent soil amendment that you can use in your gardens, containers and potting mixes instead of buying bagged peat moss.
Best of all – leaves are free!
If you have any trees on our near your property (which is true just about everywhere in New England), now is the time to stockpile at least some of those leaves for future use. You can keep leaves from blowing away using a simple enclosure made from stakes woven into chicken wire:
The leaves at the bottom of this leaf mold pile break down first, but you can use your leaf mold for mulch or as a soil amendment at any time during the decomposition process.
In New England where we get a lot of rain and snow through the year, leaves break down into leaf mold in 6 months to 3 years, depending on the type of leaves (see below). You don’t have to wait that long though, you can use it whenever you need it. The leaves will continue to break down in the presence of moisture and soil organisms.
Shredding leaves first with a mulching mower or shredder will help break them down more quickly. Shredding also reduces volume and the tendency for whole leaves to mat together, but it’s not necessary. Bear in mind that shredding may kill any cecropia, luna, woolly bear and other moth caterpillars that might be hunkered down in the leaves for the winter.
You can also mix your fall leaves with “green” materials such as farm animal manure or grass clippings to make leaf compost. A mix of about 2/3 greens and 1/3 leaves (brown) will heat up quickly and break down into nutrient-rich compost or mulch to use in next year’s vegetable beds, flower gardens and lawns.
If earthworms find your compost pile, they will help speed up the breakdown process by consuming tiny bits of leaves. Their rich castings stimulate beneficial bacteria that will heat up the pile and turn it into fine, dark humus that is pure gardener’s gold.
Leaves contain chemical tannins that are only digestable by specialized fungi that have evolved in northern forest ecosystems. Most bacteria cannot tolerate the acidity of pure leaves and do not readily break them down.
So what’s better, leaf mold or leaf compost? It depends on what you want to use it for.
Leaf mold is pure leaves with no green materials mixed in. It is broken down slowly by “cold” natural processes involving moisture and specialized soil fungi that have evolved with trees since the last ice age. Loaded with beneficial fungi (mycorrhyzae) that tree roots use to feed themselves, leaf mold is the single best mulch for use in woodland gardens and under your trees.
Leaf mold is the soft and spongy “duff” layer that you find on the forest floor of mixed woodlands in New England. If you have trees on your property as well as wooded areas with perennial native understory perennials, your tree leaves are the only fertilizer they will ever need.
Leaf compost is created by hot processes dominated by bacteria that feed upon the greens and convert their nutrients into a form that can be taken up easily by plant roots. With a higher pH than leaf mold, leaf compost is a highly-nutritious, near-perfect product for vegetables, annuals, and lawn grasses which prefer a neutral or high pH, as well as lots of nitrogen for fast growth, high yields and exceptional flowers.
Pure leaf mold is best for native plants such as the beautiful white trillium. Trees feed themselves and their understory partner plants by dropping their leaves to the ground, which are broken down by fungal networks that in turn make nutrients available to plant roots. Scratch the soil of a healthy forest floor and you can see some of these vast networks of fungi that mine the soil for moisture and nutrients.
Use leaf mold and compost as a replacement for peat moss in gardens or in potting mixes for moisture retention and soil porosity. Peat moss is not considered a renewable and sustainable product in the US because it is trucked long distances from Canada, where it’s mined from sphagnum bogs that took millions of years to produce the peat moss that we buy in bags.
Note that most earthworms are not native species in New England forests–not since the last Ice Age wiped them out, anyway. Most earthworms found in the northern US were brought here in Colonial ship ballast and have been welcomed by centuries of farmers for their capacity to rapidly turn farm waste into crop fertilizer. Earthworm populations in woodland soils is not good for long-term forest health–their ravenous appetite for leaves means that they break down leaf litter much faster than natural fungal processes, and earthworm castings (manure) feed bacteria that raise soil pH and release nitrogen, creating an environment highly favorable to invasive exotic weed species that often outcompete the natives.
If you want to create “pure” leaf mold (for native plants) without earthworms, bag your leaves and store on a surface where earthworms cannot enter the leaves from the soil below. Or place a wire cage on a hard surface to exclude them. If you bag leaves, you will need to water the leaves occasionally to encourage the moist conditions that fungi love.
Trees such as oak and beech that hold onto their leaves long after most other trees drop theirs generally take years to break down into humus. Pictured is a young Beech still holding most of its leaves in February.
Different tree species have varying levels of tannins, and leaves with the highest tannins take the longest to break down. Oak leaves, especially, are high in tannins and can take quite a few years to break down.
Fastest: Maple, Ash, Cherry, Poplar, Linden, Willow, Poplar, Elm (6 months to 1 year)
Slower: Oak, Beech, Birch (2-3 years)
Slowest: Needles from Pine, Hemlock, Spruce and Fir–not because of high tannins but these leaves have a waxy coating that slows decomposition – 3+ years minimum