Pile of leaves in an oak forest illuminated by sunlight filtering through the leaves.

Leaf Mold Magic: How to Use Fallen Leaves to Improve Your Garden Soil

Next time you walk in a forest, try bending down and taking a handful of the soil. You’ll find it dark with a delightful smell somewhere between rich earth and old leaves. 

These leaves are full of nutrients – the very nutrients that can be used to grow huge trees. And in the autumn, there are often so many leaves that it takes just minutes to pick them up. 

Unfortunately, it’s not a good idea to apply leaves directly to the soil, as they take time to break down – and make an excellent hiding place for slugs. 

Fortunately, you can make something very similar to forest soil. Leaf mold (or, in the UK, leaf mould) is not only a sustainable way to recycle fallen autumn leaves, the process of making it is incredibly simple and can be done with very limited resources.

Read on for this comprehensive guide on everything you need to know about leaf mold, including benefits, how to make it – and how to speed the process up. 

Contents

What is Leaf Mold?

Leaf mold is a type of compost that is made from autumn leaves that fell (have fallen?) from deciduous trees and shrubs. 

Leaf mold is unique in that its creation is different from other composts. Traditional compost is created by a heat-generated, bacterial process. Conversely, leaf mold is developed using a cooler and slower process that is driven by fungi. 

The resulting product is a dark, powdery material that is inhabited by multiple fungi species and detritivores. It’s also high in nutrients such as potassium, although generally lower in nitrogen than standard compost.

What are the Benefits of Leaf Mold?

Leaf mold is commonly used as a soil conditioner to improve the quality of existing soil.

Here are some ways leaf mold benefits the quality of your soil:

Improve Soil Structure 

The addition of leaf mold improves soil structure and adds organic matter. Good soil structure carries many benefits for plants, including increased water retention, drought resistance and oxygen circulation. 

May prevent some plant diseases and increase yields

Some studies show that applying leaf mold can help prevent plant diseases. A 2016 study by WH Elmer found that applying compost mulch reduced asparagus diseases, leading to an increase in yields. 

A 2013 study also found that leaf mold reduced soft rot and increased onion yield, while the 2022 study by Richardville et al found that leaf mold reduced some tomato diseases in the second year of the trial and led to an increased yield in tomatoes. 

How Long Does it Take to Make Leaf Mold?

In contrast to composting, leaf mold is created through a bacterial process – which can take as long as 2-3 years. 

However, there are methods that gardeners can implement that will greatly reduce the time it takes for leaves to properly decompose. 

How Do You Make Leaf Mold? 

Shovelling leaf mold.
Leaf mold is not hard to make, although it does take some time.

Making your own leaf mold is quite simple, and requires inexpensive materials that you most likely have in your home. 

What Kind of Leaves Should You Use?

The leaves used in leaf mold are usually autumn leaves that come from deciduous shrubs and trees. 

Not all leaves will decompose at a similar rate. Thin leaves (such as birch leaves) decompose the fastest, while tougher leaves (such as chestnut, evergreens, and conifers) take the longest to decompose. 

Making leaf mold in sacks and bins

Perhaps the simplest way to make leaf mold is in sacks. You can simply get a tough sack (old compost bags are perfect). Make some holes in it if it is air-tight, and fill it full of leaves. 

An alternative, if you live in the UK, is to use Jute Leaf Compost sacks. Designed for leaf composting, these bags are made from a biodegradable material – so you just fill them with leaves and leave them to rot down over time. Buy them in bulk and you will also find the price for each one is pretty reasonable!

Do bear in mind that the leaves will shrink dramatically in size over time. 

How to make a leaf mold enclosure

Leaves in a wire leaf enclosure.

As you can tell from a forest floor, leaves only need to be left alone to turn into leaf mold. However, a gardener also has to contend with winds and gales – which can make a leaf mold enclosure handy!

In order to make a leaf mold enclosure, you will need the following materials. 

  • Weed Smothering Membrane/Weed Barrier Fabric
  • Four Tree Stakes
  • Chicken Wire
  • Hammer/Mallet 
  • Wire/Twine
  • Shredder/Lawn Mower

How to Prepare the Leaf Mold Enclosure

  1. Cut a square of weed smothering membrane that is just over 1 square meter. This is necessary to stifle the growth of weeds and roots that could otherwise render your leaf mold useless. 
  2. Place each of your tree stakes 1 meter apart and hammer them securely into the ground. 
  3. Cut a sheet of chicken wire that is long enough to wrap around the perimeter of all four tree stakes, leaving a few extra inches to overlap. Using your wire/twine, fasten the chicken wire together to create an enclosure. 

When the cage is set up, you can begin filling the enclosure with leaves. Shredding the leaves first with a lawn mower will help reduce their volume, allowing you to stuff more leaves into the cage. Over time, the leaves will begin to rot and the pile will shrink to two-thirds of its original size. Expect the leaf mold to be ready for use within one to three years. 

You can also buy ones pre-made on Amazon, such as the leaf enclosure below:

MTB Garden Wire Compost Bin 30x30x24 inches, Black, Garden Bed Fencing

Where is the Best Place to Build a Leaf Mold Pile?

You will want to protect your leaf heap from direct sunlight, especially during the summer. Moisture and shade will be your friend during this process. The ideal location to build a leaf mold heap is a shady area that receives rainfall. 

In addition, it is best to place your leaf mold enclosure in an area that is away from foot traffic, yet still easily accessible. Leaf mold piles can release spores that trigger mold allergies in people who are sensitive.

How Do You Make Leaf Mold Quickly?

Combining leaves with grass clippings can increase the speed of decomposition – but also the properties of the compost.

As previously discussed, leaf mold is a timely process that could take up to three years to properly decompose. If you are short on time, there are three ways to expedite the process: shredding the leaves, providing shade and water, and increasing nitrogen. 

Let’s break down these three methods:

Shade and Water 

The molding process can be accelerated by slowing down the rate of evaporation in the leaf pile. Move your leaves to a shady location; this will help the leaves stay moist as they break down. When adding new leaves to the pile, be sure to add water each time. 

Shred the leaves

Using an electric shredder such as the one below, break down the leaves in smaller pieces. The goal here is to increase the surface area, which in turn reduces the time it takes for microorganisms to convert the material into leaf mold. 

WORX WG430 13 Amp Electric Leaf Mulcher

Increasing Nitrogen

The microorganisms that produce ordinary compost primarily feed off of two elements, carbon and nitrogen. While autumn leaves are abundant in carbon, they lack nitrogen – the average carbon to nitrogen ratio of leaves is 60:1, while the ideal ratio to maximize decomposition is 24:1. Because of the lower nitrogen in leaf mold, fungus does most of the work – and does it more slowly than the mesophilic and thermophilic bacteria in a standard compost pile. 

One way to speed up decomposition is to increase nitrogen level. This is easy to do by adding greens (materials high in nitrogen) such as grass clippings. For a super fast composting process, shred the leaves before adding the high nitrogen material.  

Strictly speaking, this is traditional composting rather than leaf mold, but while the properties of the finished product may be different, it will still be great for your soil. 

How do you use leaf mold?

Leaf mold has a multitude of uses for creating stronger, healthier plant. Here are just a few examples of what one can do with leaf mold:

Traditional: Dig it in

Work your leaf mold into the soil until it is uniformly mixed in. The introduction of leaf mold will increase moisture retention and improve the oxygen circulation in the soil. However, do bear in mind that when you dig your soil, you can damage valuable soil organisms such as Mycorrhizae Fungi

Spread it on your soil

An alternative to digging your leaf mulch in is to spread the leaf mulch on your soil as a compost. The compost will be gradually worked into the soil by microorganisms. This saves on work, avoids damaging soil structure and avoids surfacing weed seeds. 

Use it as a mulch around plants

Spread a layer of leaf mold that is 2 inches thick around the base of your plants. Mulching plants is beneficial for many reasons: it helps retain moisture and regulate soil temperature by reducing evaporation, it stifles the growth of weeds, and deters pests from crawling onto your plant. 

Use it as a seed starting mix.

Leaf mold has an airy texture and moisture-retentive abilities which make an excellent choice for seed starting. When seeds start their early stages of life, they require consistent moisture and soft soil that their budding roots can easily navigate. Using leaf mold in place of standard potting mix ensures fortified seedlings for a new growing season. 

Is Leaf Mold Dangerous?

For all of its benefits, it is important to still keep in mind that leaf mold is decomposed organic matter, and therefore can contain hazardous mold spores within it. These mold spores can trigger an allergic reaction within those who are sensitive to mold, especially when you have been working with high quantities of leaf mold. On very, very rare occasions it can be fatal

Those with underlying health conditions are advised to exercise more caution before handling leaf mold. In healthy individuals, the risk of becoming sick from mold spores is low, yet proper protective procedures are still highly recommended. 

You can protect yourself from these side effects by wearing a mask to stop spore inhalation. In addition, working with gloves and keeping your distance from the leaf mold pile also reduces your risk of falling ill. 

Frequently Asked Questions

What is the difference between leaf mold vs. leaf mould? 

The only difference that separates the words “mold” and “mould” is a geographic one. Mold is used in the United States, whereas mould is used in countries like the UK.

Can I collect leaves that I found on the street? 

Piles of leaves gathered on pavements can be a tempting target for the amateur gardener – especially for those who live in cities. However, a study by the UK Environment Agency found that leaves on streets may contain carcinogens. Other studies have found that urban leaves may contain heavy metals. If you plan to make large quantities of leaf mold, it may be best to avoid roadside litter. 

I don’t have chicken wire. What else can I use to store my leaf mold heap?
You can also use compost bins or a plastic bag. Make sure to puncture holes throughout the enclosure in order to increase the airflow.