Leaf Mold: Nature’s Compost

One of the best parts of the fall season is that sweet, sweet crumbly leaf mold – something I look forward to every year. Not only is the intense heat of summer cooled off, but deciduous trees have dropped dead leaves onto the soil surface to fertilize the earth. 

It’s a wonder why so many people rake them up and give them to waste collection personnel to be disposed of. Spreading leaves in the garden is such a powerful tool. The earth invented it! This is how lush forest floors practice regeneration on their own.

So why not mimic what nature has to show us? By using fallen leaves in our gardens, we help the soil retain moisture, and as they decompose, they feed nutrition to the soil below. The collection and use of leaf mold in the garden is also a super simple process. 

So let’s talk about leaf mold and how gardeners can use it in their garden spaces! 

What is Leaf Mold?

Put simply, leaf mold is the result of the decay of fallen, partially decomposed leaves. A leaf pile is a powerful thing, as it converts raw leaves into this enrichment tool. The contents come from deciduous trees, but may also include weeds or even grass clippings. People use leaf mold as a soil conditioner or as mulch, spreading it on beds surrounding plants. As leaves decompose, they return essential nutrients to the earth and lock in moisture. They also keep plant roots warm during winter, and house overwintering insects – namely beneficial predator insects and pollinators. This is why I wince every time I see people giving this straight-up golden resource to the landfill or the municipal composter. 

Leaf mold has lots of uses in a yard or garden area. We’ll touch on that later in this piece. 

Benefits of Leaf Mold

Leaf mold is the best additive, especially when it comes to building soil structure. It’s an abundant natural resource that is practically free, only requiring the expenditure of the energy it takes to collect it and break it down. When we say it holds moisture, we mean it. Leaf mold holds just as much moisture as peat moss. It’s full of nutrients. Not only are major nutrients nitrogen, phosphorus, and potassium present, but several micronutrients that support plant growth are present as well. It’s not only beneficial for soil structure but has a linked benefit of attracting earthworms, who travel upward in the soil to consume and process decaying autumn leaves. You can spread it on garden beds, or incorporate it into your soil as an annual soil refresher. Alternatively, let leaves do their thing in your garden. 

While they sit there, they decompose and feed your nearby plants or grass. They contain tons of beneficial bacteria, and they provide a habitat for overwintering insects of all kinds, especially your garden friends. Ground beetles, centipedes, millipedes, pillbugs, and spiders all help disintegrate the leaves. Pollinators like wasps, some bees, and moths make themselves a home in decaying leaves for winter. They emerge again in spring to do the work of pollinating your plants to help you produce veggies. 

Collecting Leaves

If you’d like to create your own pile as a source of leaf mold, there are a few things to consider. Whether you want to simply collect fallen leaves from the garden, or find a source elsewhere, think about the size, type, and age of your leaves to adequately plan for their usage. Some leaves require a bit of processing before they’re actually beneficial to the garden soil, while others don’t require any. 

Leaf Size

Smaller leaves or thinner leaves decay quicker and more easily than thicker or larger leaves. Shredded leaves have an added fire that will decompose even faster than some small leaves. The more variety of sizes in your pile, the better the content. As a result, you definitely should think about different sizes of fallen leaves when you make leaf mold. 

Leaf Type

Size affects how long it takes for leaves to decompose, and so does the species. Oak leaves, for instance, take longer to fall apart than yellow anemone, which is practically on the opposite end of the decay spectrum. Maple and sycamore trees have a similar rate of decay. Mixing different types will promote higher rates of decay for some types that usually take more time to become leaf mold than others.

If you notice your neighbors trying to haul away some of the leaves from their yard, consider asking them if you can have them instead! It saves them some energy and adds variance to your supply of leaf mold. Diversity is a huge part of inherently healthy natural systems. 

Another important consideration that plays into creating leaf mold is knowing which plants contain herbicidal compounds like juglone. Black walnut, American elm, and hickory trees secrete these compounds. Let any juglone-containing plant matter decay for at least 2 months before using it as mulch or in gardens. In this case, build your composting pile and let the pile do its thing, but let the pile sit for some extra time before using it to be sure the natural herbicides decay. After it’s broken down into a deep brown or black, soft mass, it will be just as good as non-allelopathic types. 

Leaf Age

Think about the age of the leaves you’re using. While that’s certainly a consideration in the topic we just discussed, it’s also something to consider when it comes to the freshness of leaves. Fallen leaves – unless they contain juglone – can usually be used right away with just a little bit of processing. But new leaves and fresh leaves require a lot more processing before they are actually beneficial in the garden. These can become matted together as they decay if they’re full-sized. Shredding leaves breaks them down into smaller sizes, enabling microbial life to start to break them down and help us make leaf mold that will enrich our soil.

In addition, freshly-fallen leaves have more nitrogen than those that have been sitting on the ground for a while. Those sitting for a time gradually turn brown and oxidize off their nitrogen, leaving behind only carbon. Carbon is beneficial to the soil as it holds onto moisture and takes longer to break down. Nitrogen aids in future plant growth. A mix of both is ideal when you’re composting, as a good carbon to nitrogen ratio helps in decomposition.

How To Make Leaf Mold

Making leaf mold can be as complicated or as uncomplicated as you want. There are different ways to process leaves for use in gardens. Such processing usually speeds up the decay of leaves. Once gardeners have gathered this practically free resource, it’s time to decide which of these methods is best for their gardening style.

Fast Methods

One fast way to promote decomposition is to rake up the leaves, bag them up, poke holes in the bag, and allow the heat in the bag to decay the leaves more quickly than they would if they sat in the open air. You can wet the leaves within to speed up the process too, but make sure the leaves aren’t too wet. A handful of moist leaves should have the consistency of a damp sponge rather than be dripping with water. Too high of a moisture level will actually slow the process down, hence the need for holes in the bag. One great resource for keeping those leaves moist is urine, which provides nitrogen in the form of urea – but if you’re squeamish, just water will do! If you’re hesitant to use plastic, consider a compostable bag that will break down gradually with the leaves.

Other than a bag, there are more options for containers you can use to quicken the decay. A compost bin, whether a wire bin, open bin or enclosed, is an excellent choice. So is your basic compost tumbler. Note that it’s best to ensure your leaves make direct contact with the soil, so place any stationary bins directly on the ground rather than concrete. Compost that touches the earth ensures interaction with the microbiome of the soil there, creating a rich source of gardening material that will assist in appropriate water retention and enrich any site. Consider using a compost thermometer to monitor the temperature in your pile to ensure it stays optimal. You don’t have to ensure really hot composting for this sort of compost, but heat during decomposition speeds it up.

Note that shredding leaves will also quicken decay. For faster production of leaf mold, shred leaves before they go into the garden or the leaf mold pile. Fast methods are great if you need to fill garden beds quickly for a soon-to-happen season. They’re also great for gardening in warmer seasons when fruits and veggies need conditioning now, rather than later. Hot methods are especially good for composting weeds because they kill remaining seeds that could germinate. 

Slow Methods

Pile leaves together and let them sit on the soil surface to decay over time. This is best with fallen, carbon-rich leaves like those in the fall. I find this method most beneficial for use in garden beds when shrubs and veggies die away or enter dormancy as it acts as a mulch over the winter while it decays. In the following spring, I add soil to the decayed leaves. You can also keep a pile next to your compost bin for a consistent source of brown matter. The larger the pile, the faster the process. A surface area of a 4 to 5-foot across pile that’s a few feet deep gets broken down much faster than a thin layer on the earth’s surface. 

Because not all leaves are good for gardens right away, slower pile methods are sometimes preferable. As bacteria consume the leaves, essential elements of a healthy microbiome build up and fill the mold with that goodness you want. A slower decomposition process means less of the beneficial parts of the mold are burnt up in a quicker process. Slow methods are also great when you have time to wait. They don’t require a lot of effort and make the free part of this resource truly free. 

How To Use Leaf Mold in the Garden

Think about why you’re making leaf mold. What is it for? Will it be mulch, or will you fill your compost bin with it? Will it be a source of water retention or a method of keeping vegetation warm in winter? You may even want to make leaf mold to condition your soil. Whatever the reason, know you are gardening with one of the best amendments for your beds!

Mulch

There are tons of different types of mulch out there – straw, wood chips, and more. But if you’d like to use leaf mold as mulch, apply it around the garden, leaving a couple of inches of space between it and the base of your plants. It’s great for gardening in winter when the air is cold and all the leaves are dead. I’ve used it to cover my garden in winter, protecting roots that wait for spring to come out of dormancy. In this case, I simply fill the bed with leaves. No shredding and no spacing are required, although if there are a lot of leaves, you can certainly shred to pack more into the available space. If they haven’t all decayed by the spring, you can compost larger bits and work the rest into the soil to prepare it for gardening. 

Composting

We’ve already talked about the basics of composting leaves. But we can’t emphasize enough how beneficial fall leaves are in composting processes. Fallen leaves provide a much-needed source of brown waste that is crucial to help heat your compost pile. Keep your pile of leaves at the compost site, and mix some in when you add green matter like coffee grounds. You can also cover the pile with leaves in the winter to keep the organisms within safe. Worms love it, too – you can use it in your worm tower or bin to feed your composting worms. As a carbon-dense material, it is excellent bedding for worm bins.

Soil Conditioner

Another way to incorporate this mold into your gardening practice is to mix it in with soil, where it acts as a rich conditioner. In this case, it’s best to shred the leaves before composting them, as that way they have a finer size and can decay quickly. Spread it over the garden bed, and around plants, not directly on them. 

Lawn Fertilizer

While many people use seeding and turf builders as the primary method of fertilizing a lawn, this mold is just as effective. If your grass is growing under a deciduous tree, it’s as easy as letting them fall and decay over fall and winter. Otherwise, you can rake them up, and spread them across the lawn after they decompose. Shredding the material will assist in decay. 

Frequently Asked Questions

Q: What is leaf mold good for?

A: It’s great for gardening! Use it to mulch, fertilize, and protect your yard. 

Q: Is leaf mold better than compost?

A: Not necessarily, but it can be incorporated into a composting bin. 

Q: How long does leaf mold take to make?

A: It depends. If you shred it, not more than a month or two. Full-size it can take 6 months to a year to decompose. 

Q: Can you plant directly into leaf mold?

A: You can, but it’s better to provide a well-thought-out blend of soil and amendments that is optimized to the needs of what you’re growing. Gardening with leaf mold is great, but that doesn’t mean it should be the only thing you use!