Leaf mold is so simple to create and beneficial for your soil. Just pile your fall leaves and let them decompose and in time you’ll have this organic soil amendment.
Just like homemade compost, creating leaf mold is another way to make use of free, natural resources right in our own yards.
Using Leaves to Improve Soil
Over the years we’ve spent a lot of time and energy ridding our gardens of fall leaves.
Remember the burn pile?
For decades it was common to create massive piles of autumn leaves and set bonfires, letting all those dry leaves go up in smoke.
Eventually, municipalities started offering collection services and we would—and still do—rake, bag, and send away fall leaves—sometimes to landfills, but now more likely to be repurposed as mulch.
Today many of us prefer to “leave the leaves,” recognizing the value of this free, organic garden asset for mulch and improving the soil.
Creating a leaf mold pile is one way to make use of this leafy goodness.
What is Leaf Mold?
Leaf mold is simply decomposed leaves.
The name leaf mold (also spelled leaf mould) is rather unfortunate as it sounds like a fungal disease—and there are fungal diseases affecting plants called “leaf moulds” including black leaf mould (Pseudocercospora fuligena) and tomato leaf mould (Passalora fulva)—but that’s not what we’re discussing here.
Homemade leaf mold really is just old, rotted leaves. And it pretty much makes itself as you’ll see.
How Does It Benefit the Soil?
When leaves are rotted down into leaf mold and added to soil, it can help improve structure, particularly with sandy soils. It also adds organic matter and improves water retention. This shows a simple way to test your soil composition for sand, silt, and clay.
Leaf mold is also used as an ingredient in some potting mixes where it offers those same benefits.
Used as mulch, leaf mold can protect plant roots and reduce soil erosion.
From an environmental perspective, by using fall leaves at home, we reduce the overall carbon footprint compared to the resources required for municipal collection systems.
What Is The Nutritional Composition of Leaf Mold?
Does leaf mold offer any nutrients?
You would think the answer to this would be simple but it’s not.
Some garden guides say leaf mold mainly improves soil structure and not to expect it to add any nutrients to your soil.
Others insist leaf mold must be a good source of nitrogen since plants can store three-quarters of their nitrogen in their leaves. And certainly there are other micro-nutrients in there as well?
But fall leaves are different than spring and summer leaves.
As winter approaches, trees claw back nutritional resources including nitrogen from their leaves and store them in other parts until they are needed again in spring. During spring and summer those leaves are nitrogen-rich. By fall, amounts are waning.
The main study that gets cited is from Rutgers University in the 1990s. It looked at nutrients in fresh, fallen leaves—not leaf mold—collected in municipalities in New Jersey.
That study showed a wide range of nutrients in the soil, but at low concentrations—about the equivalent of 1 – 0.2 – 0.4 of N (nitrogen), P (phosphorus), and K (potassium).
Is it the same in our gardens? Without testing, we cannot know.
How Do You Make Leaf Mold?
If you have a lot of trees on your property you know what a thick, slimy mess masses of fall leaves can make if left in place for the winter, smothering the grass.
That’s why, when we say “leave the leaves” we mean, if you can, keep them for your garden—don’t send them away. But don’t ruin your yard in the process either.
Creating leaf mold is as simple as it gets: pile up leaves, let rain and air reach them, and over time they rot down into earthy soil-like stuff we call “leaf mold.”
To make leaf mold, wait for a day when the leaves are dry on the ground. Use your lawnmower to grind them into bits. It may take 2 or 3 passes to mulch them down.
Next, rake them onto a tarp and pull them over to your designated leaf mold area.
Three Ways to Create Leaf Mold Piles
Leaf Mold Bin
A leaf mold bin can be anything that holds the leaves in place while allowing rain and air in. The size and shape will depend on the space available and how many leaves you want to save. Grinding them down with a lawnmower greatly reduces the volume.
The traditional way is to create an open wood frame with chicken wire sides. Keep the bottom open so the leaves sit on the ground.
You could also use untreated wood pallets to form a big, open box.
Lightly Cover Leaves With Soil
I have a large patch of bare soil at the back of my yard (where nothing grows). I spread out the chopped-up leaves there and just lightly sprinkle them with damp soil to keep them from blowing away. It’s the same area I keep all sorts of yard waste for decomposition.
Bag the Leaves
Another option is to poke air holes in a large yard waste bag (or heavy-duty trash bag) and fill it with moistened, chopped leaves. They’ll need to stay moist and have air circulation while you wait.
No matter which way you do it, the leaves will gradually rot and transform into a dark crumble with an earthy smell similar to a good compost.
How Long Does It Take?
How long it takes fall leaves to become leaf mold depends on the leaves and conditions. It’s a much slower process than compost.
Whole leaves might take two years to break down. Maybe less, but sometimes even longer.
Chopped leaves are faster.
I’ve found the combination of chopping up the leaves with the lawnmower and spreading them out over bare soil works best, taking just under a year to become leaf mold.
If you’re impatient, you can use them at any stage as mulch or “browns” (carbon) for food composting.
Why Do Leaves Alone Decompose Slower Than Compost Piles?
It’s all about the bacteria!
On their own, fall leaves take so long to decompose because of their high carbon (C) to nitrogen (N) ratios, which can be 50-to-1 and sometimes higher.
A good compost pile has a C-to-N ratio between 25-to-1 to 30-to-1 which is optimal for the hard-working bacteria that turn our scraps into compost.
Too many “browns” or carbon-rich items and the entire process is slowed down.
With the carbon ratio so high in a leaf pile, instead of those fast-working bacteria, we’re relying on slower-working fungi to get the job done. Which also means that our leaf piles won’t warm up as much as our compost piles do.
Just like composting fruit and vegetable scraps, keeping leaves for leaf mold is another smart way to make use of existing resources to improve our gardens.
Grind your fall leaves down with a lawnmower to accelerate the decomposition process and create a leaf mold pile.
Allow rain and air to reach the leaves and watch as they gradually break down into an earthy soil-like amendment over the coming months and years.
Apply leaf mold to your garden beds to improve soil structure and water retention.
- Plant Nutrients in Municipal Leaves | Dr. Joseph R. Heckman, Daniel Kluchinsh, Dr. Donn A. Derr | Rutgers University
- Soil Food Web | Elaine Ingham | USDA Natural Resources Conservation Service
- How to Check if You Have Well-draining Soil | Empress of Dirt
- What is Soil pH and Why it Matters | Empress of Dirt
- What is No-Dig Gardening? | Empress of Dirt
- Free Printable Fall Garden Checklist | Empress of Dirt
~Melissa the Empress of Dirt ♛