Leaf mold: how to turn fall leaves into soil conditioner

Leaf mold is what fall leaves turn into when fungi break them down. To make it, shred the leaves with a mower, pile them at least 3 feet (1 m) wide and tall, and keep the pile damp. You don’t need to turn it. Shredded leaves are ready in about 6 months, and whole leaves take 9 to 12 months or longer. Leaf mold is low in nutrients, so use it as a soil conditioner or mulch, not as a fertilizer. For faster results, mix the leaves with coffee grounds or grass clippings to make leaf compost.

Want the easiest option? Pile up leaves on their own and wait for leaf mold. Want finished material sooner? Add a nitrogen source and build a compost pile. Only have a thin layer of leaves on the lawn? Mow them into the grass and skip the pile.

Save your leaf piles

I get so sad when I see bags of leaves on the corner, ready to be carted away. All that organic matter is leaving the yard. We get leaves once a year. They should be saved and treasured, not trucked to a landfill.

Once you love leaves as much as I do, you may want to ask your neighbors for theirs. Hold off unless you know their trees weren’t sprayed with pesticides. Your own leaves are the safest choice. Skip black walnut leaves. Nebraska Extension warns that they contain juglone, which stunts some garden crops.

Making leaf mold compost with fall leaves

In the wilder areas of our yard, I let the leaves stay on the ground as mulch. These areas used to be covered in bark mulch, so the leaves won’t harm anything like grass. The leaf mulch keeps the weeds down and returns nutrients to the trees.

On our lawn, the leaves have to go. A thick layer of leaves can smother grass, and Nebraska Extension says a buildup also raises the risk of snow mold. Mow or rake leaves often so they don’t pile up.

We turn the leaves that land on the grass into leaf mold. First, we mow over them with a mulching lawnmower. Shredding speeds up decomposition. It’s much easier to shred leaves in place than in a pile (we know this from experience). UMass Extension recommends mowing when the leaves are dry and making 3 to 4 passes with sharp blades. Then we rake the shredded leaves into piles and use a wheelbarrow to move them to the bin.

Raking leaves in the crisp fall air is a great workout. I’d take raking leaves over a run on the treadmill any day.

Leaf mold vs. leaf compost

Leaf mold and leaf compost both start with fall leaves, but they break down in different ways. UF/IFAS Extension explains that leaf mold uses only leaves, decayed by fungi. It’s a cold process that needs no turning. It’s less work than hot composting but slower.

Leaf compost mixes leaves with nitrogen-rich material like coffee grounds or grass clippings. The added nitrogen feeds the microbes, and the pile heats up and finishes faster. The rest of this guide covers both. Our bins hold a mix, so what we make is closer to leaf compost.

Making leaf compost in bins

My dream setup is a three-bin system: one for building, one for turning, and one for finished compost. The first bin gets new material, like shredded leaves. Once the pile in the first bin heats up, we move it to the second bin. Moving it mixes and turns the pile, which helps it break down. The third bin stores finished compost until we use it.

This isn’t the fastest way to compost, but it’s the most practical for our household. I don’t have time to measure the temperature, check the moisture, and turn the pile all the time so my compost is done in a couple of months. But I do like having lots of compost, and I’m willing to wait for it.

We have just a two-bin system, so we don’t have a storage bin. We spread finished compost around the yard as soon as it’s done.

Adding nitrogen to speed up leaf compost

Do leaves alone make good compost? They break down on their own, but it takes a long time. Compost needs four things: carbon-rich material, nitrogen-rich material, water, and air. Carbon-rich materials like dry leaves and shredded paper are brown and dry, and they give the pile bulk. Cornell notes that nitrogen-rich materials like grass clippings, plant cuttings, and vegetable scraps tend to be green and moist.

Dead leaves are full of carbon, so a bit of nitrogen helps get them going. Coffee grounds are a good source. Save your own, or ask a local coffee shop. Some give away used grounds for gardens.

Carbon to nitrogen ratio for composted leaves

Aim for a pile with about 30 parts carbon to 1 part nitrogen by weight. Cornell Waste Management Institute lists autumn leaves at 30 to 80:1, coffee grounds at 20:1, and grass clippings at 15 to 25:1, based on this small-scale composting guide. Coffee grounds have more nitrogen than leaves, but they still hold 20 times more carbon than nitrogen. UMass Extension suggests about 3 parts brown material to 1 part green.

It’s hard to build the perfect pile right away, because ingredients vary. Some leaves carry more carbon than others. Some get mowed with grass clippings, and some get raked up with no grass at all. Some grass clippings are dry and not all that rich in nitrogen. Get close, and adjust your recipe as you go.

If the ratio worries you, remember that leaves break down in nature without any help. Most leaf mold is made with just leaves.

Without added nitrogen, leaves are slow to break down. Too much nitrogen causes problems too. UMass Extension says ratios below 25:1 can turn a pile anaerobic and smelly, as extra nitrogen escapes as ammonia gas. Because an exact 30:1 ratio is hard to hit, I lean toward extra carbon. I’d rather wait a bit longer than have a slimy, smelly mess. Experiment with your ingredients and learn what works in your yard.

“Never ever throw out leaves unless they are seriously diseased. Collect them from other people. Use them in the composter, rake them up on top of borders where they will be broken down by worms.”

Thrifty Gardening: From the Ground Up, by Marjorie Harris

Supplies for making leaf mold and leaf compost

• Fall leaves (most deciduous leaves work)
• A compost bin, wire bin, or spot for a heap
• A mulching lawnmower
• A rake
• A wheelbarrow
• Coffee grounds, grass clippings, or manure (for leaf compost)
• A hose or watering can

How to make leaf mold from leaves alone

1. Mow the leaves while they’re dry. Make several passes to chop them into small bits.
2. Rake the shredded leaves into a pile or a simple wire bin. UF/IFAS Extension recommends a pile at least 3 feet (1 m) wide and 3 feet tall.
3. Moisten the leaves as you build the pile. Keep them damp, but not soaking wet.
4. Water the pile now and then in dry weather.
5. Wait. Illinois Extension says shredded leaves are ready in about 6 months, and whole leaves take 9 to 12 months. Tough leaves can take up to 2 years.
6. Dig from the bottom or center of the pile, where the leaves have broken down the most.

How to build a leaf compost pile

1. Mow and rake the leaves as above. A few grass clippings mixed in add nitrogen.
2. Spread a layer of shredded leaves in the bin. Colorado State University Extension says layers should be no more than 2 inches (5 cm) deep for fine materials and 6 inches (15 cm) for coarse ones.
3. Add a layer of coffee grounds or other nitrogen-rich material on top. Keep the 30:1 ratio in mind, and remember that it’s by weight.
4. Moisten the pile with the hose or watering can. If you have some garden soil or old compost, sprinkle a bit on to add microbes.
5. Repeat with each new load of leaves, adding nitrogen and water each time.
6. Turn the pile once the bin fills up. We turn ours after about 2 weeks. The more often you turn it, the sooner it’s done.

You can get fancy with compost later, measuring the temperature, perfecting the moisture, and weighing your ingredients. For now, just get started. Adjust as you go.

Leaf type, moisture, and temperature all change how fast a pile breaks down, according to UF/IFAS Extension. Piles slow down in winter. Shredded leaves break down faster than whole ones. Change things up and watch how your pile behaves.

How to use your leaf mold compost

I spread a 1 to 2 inch (2.5 to 5 cm) layer of leaf mold over my garden in fall. It protects the soil over winter and smothers weeds. UGA Extension also suggests a 2-inch layer as mulch for a no-till garden. Around young trees, I spread a thin layer as mulch and keep it off the bark, since moisture against bark invites disease. Sometimes I top it with fresh shredded leaves for extra winter protection. For more ideas, see how to protect young trees from winter damage.

Why leaf mold is worth the wait

Turning leaves into leaf mold keeps them on your property, so they don’t get trucked away or take up space in a landfill. And you get free soil conditioner for your garden.

Leaf mold is low in nutrients, so it’s not a fertilizer. Rutgers Cooperative Extension says composted leaves are about 0.5 to 1 percent nitrogen and release little nitrogen in the first season. Plants growing in soil amended with leaf compost may need extra nitrogen. Leaf mold improves soil structure, drainage, and water retention, and it gives earthworms and other soil life a home.

It also works in beds and raised beds. Mix it into the top few inches of soil, or use it to fill a raised garden bed. Illinois Extension notes that leaf mulch has no significant effect on soil pH. Even acidic oak leaves break down to neutral or a touch alkaline.

Leaf mold is a total win-win!

Leaf mold FAQ

How long does leaf mold take?

Anywhere from 6 months to 2 years, according to UF/IFAS Extension. Shredded leaves finish faster than whole ones.

Do you need to turn leaf mold?

No. Fungi break down the leaves without turning, so a leaf mold pile can sit. Leaf compost with added nitrogen does benefit from turning.

Which leaves make the best leaf mold?

Most deciduous leaves work. The RHS finds that oak, birch, beech, and maple work best. Tough or waxy leaves and conifer needles take longer, up to 2 to 3 years. Leave black walnut leaves out.

Can you use leaf mold in seed-starting mix?

Yes. UF/IFAS Extension says you can add sifted leaf mold to seed-starting mixes or use it on houseplants to hold moisture. Sift out twigs and large pieces first.

Does leaf mold smell?

Not much. UF/IFAS Extension notes that leaves alone don’t produce the odors that food scraps and grass clippings can.