Every year, the leaves change colors and fall to the ground creating a picturesque landscape that for some causes a lot of confusion.
It seems that no matter whom we ask, we’ll receive a different answer to the big question of what we should do with those leaves.
We hear experts in TV advertisements or magazines tell us to leave those leaves on the ground to fertilize the soil.
Yet we don’t understand why the leaves should be left alone, and we may also question what happens to them the longer they are left in the yard.
Do Leaves Decompose?
Yes, leaves do decompose over a length of time.
However, the size, weight, and distribution of the leaves play a role in how quickly they will decay.
Additionally, access to air, water, and temperature can impact decomposition rates.
Natural or man-made disasters can also play a role in leaf decomposition.
Trees that are disturbed in a quick and traumatic way, such as by explosions or fires, decompose differently than a tree that has naturally died and is left to decompose on its own terms in the forest.
Even in the colder winter months, fallen leaves are still able to decompose underneath the snow.
In fact, they provide insulation to the ground underneath trees or shrubbery.
Depending on how thick the layer of leaves was, there may still be an inch or two remaining on the ground once the snow melts.
The remaining leaves can be gathered, mulched or shredded, and used as natural fertilizer in garden beds.
How Long Does It Take For Leaves To Decompose?
Several factors impact how long it takes for leaves to decompose including, size, distribution, exposure to air and water, lignin, and climate.
1. Size And Distribution
The size of the leaves can play a role in the length of time it takes for them to decompose.
Leaves tend to fall to the ground directly underneath the tree and stay in one place, matted together.
This creates a barrier that air and water cannot get through and in response causes leaves to decompose at a slower rate.
The larger the leaf, the heavier and more matted that barrier can become as they layer on top of each other.
Leaves that are shredded and then dispersed in a thin layer allow for air and water to filter through, which helps the leaves to decompose quicker.
Many mowers can shred leaves into a finer substance.
Another option is to chop the leaves using gardening shears, run them through a leaf shredder, or utilize a hand-held vacuum with the capability to shred.
2. Air And Water Exposure
Moist leaves will decompose quicker than very dry, brittle leaves.
However, if the leaves are drenched in water, the air is prevented from infiltrating and increases the amount of time it takes to decompose.
An example of optimal leaf decomposition includes shredded leaves, distributed in a thin layer over a wider space, which can then absorb the morning dew from the ground without becoming drenched.
The cell wall of plants contains the metabolite lignin.
Lignin is a naturally occurring phenolic polymer that gives leaves its weight, composition, and structure.
In other words, the woody, rough texture of leaves is caused by lignin.
Lignin is found in most plants and plays a role in protecting the plant from decaying quickly.
The climate also affects decomposition as areas with cooler and drier climates experience a slower decomposition rate.
Greenland is just one example of an area that experiences both a relatively dry and cool climate throughout the year.
Areas that experience a warmer, more moist climate experience a faster decomposition process in leaves.
Examples of areas that experience this type of climate are the Amazon Basin and the Philippines.
As Leaves Decay, Do They Turn Into The Soil?
As leaves decay, they become part of and enhance the soil.
However, soil is not made up entirely of decomposed leaves.
Therefore it is difficult to state that leaves eventually become soil.
Soil is quite complex and is made up of mineral particles, organic materials, the air it is exposed to, water, rock, and even living organisms.
Decomposing plants, or leaves, play just one small part in soil formation.
Soil is constantly being formed and has 3 to 4 horizons or layers.
These are the A, B, and C horizons.
The majority of the soil is actually formed from the breakdown of rocks.
Decaying leaves play a role in creating a fourth horizon, called the O horizon.
This horizon is made up of the decaying plants on the top surface of the soil.
Does The Soil Benefit From Decaying Leaves?
Leaves that are left to naturally decompose form a barrier or “natural mulch” which helps prevent weeds from growing in that area and also fertilizes the soil as they break down.
However, there is an extended length of time that it takes for decaying leaves to get to the point of being beneficial to the soil.
Therefore, shredding leaves and dispersing them lightly across a larger ground area can help speed up the process.
As leaves break down, the soil underneath will absorb the nutrients and carbon.
Each tree and plant variety contains a slightly different level of carbon.
According to the USDA, approximately 50 percent of the tree’s structure (leaves, trunks, branches, and bark) is made up of carbon.
As the various parts of the tree structure decay, that carbon is released into the soil and those nutrients can be utilized for new tree growth.
Additionally, as trees decay and disappear, this creates more space, air, and light for surrounding trees to thrive.
It also provides more space for leaves to spread out and decay without matting together.
The amount of carbon that is released into the ground for new life is also dependent on the matter in which the leaves die.
For example, forest fires cause burning trees to release carbon very quickly which is absorbed directly into the atmosphere.
The burned soil that has been damaged by the fire is unable to absorb the carbon before it has been absorbed into the atmosphere.
An example of slow-releasing carbon is when a tree naturally dies and falls to the ground.
The leaves, branches, trunk, and bark of the tree decays over a long period of years and slowly release carbon into the ground to be used for new life within the forest.
2. Diseased Trees
The leaves from a diseased tree are also infected.
As those leaves fall and begin to decompose, they may grow diseased spores which can be released into the soil and cause further disease to spread among the plant life in that area.
What Is The Decomposition Process Of Leaves?
As leaves decompose, they are part of a “soil food web”.
The Soil Science Society of America describes this soil food web as being composed of three parts which include invertebrates, mold, and the release of water and inorganic nutrients.
- Invertebrates – Invertebrates include earthworms, beetle larvae, slugs, snails, and more, which are all invertebrates that thrive by creating their homes in the soil. These invertebrates eat and shred the leaves into small pieces. Soil bacteria and fungi feed on these pieces and further mulch the leaves into a litter. Mowing the lawn or hand shredding leaves play a role in speeding up this process. Areas of dense forest experience this process at a slower rate due to leaves falling naturally and in thicker masses.
- Mold or Fungi – If you have ever looked at the underside of a leaf and seen what appeared to be a white mold, you are correct. Scientists call this mold, fungi, and it is an important part of the decomposition process. The fungi send out threads of hyphae, which act like roots. Acids and enzymes are released by the hyphae, which break down the once-living plant materials.
- Release of water and inorganic nutrients – The resulting accumulation of litter and mulched leaves continues to decompose, which causes water and inorganic nutrients to be released into the soil below. These inorganic nutrients include nitrogen and phosphorus, which are what new plants absorb and utilize to grow.
Speeding Up The Decomposition Process
It is not necessary to try to speed up the process, but creating a leaf compost pile can help to speed up the length of time it takes for leaves to decompose naturally.
All leaves are different, therefore all leaves compost differently.
“Good” leaves for creating a successful composting pile are those that have lower amounts of lignin and higher amounts of calcium and nitrogen.
Examples include ash, maple, and fruit tree leaves.
“Bad” leaves for composting are leaves that have a higher amount of lignin and lower amounts of nitrogen and calcium.
Examples include beech and holly tree leaves.
Some plants, like eucalyptus and black walnut, already contain a natural herbicide that decreases decomposition rates and prevents germination.
How To Compost Leaves
It is best to gather the leaves in your yard by mowing and bagging them.
The next step is to finely shred the leaves.
Some mowers may have a shredding attachment.
Another option is to place leaves in a garbage can or other large container and use a string shredder.
After shredding, the leaves are considered to be “brown” material.
It is important to add “green” material to the compost mix as well.
These are plants that are higher in nitrogen.
This might be grass clippings or even food waste.
Another option is to add a compost accelerator which increases microbes within the compost.
The compost mixture should be turned 1-2 times per week, adding more “green” materials of choice into the mixture.
Lastly, keep the compost pile moist by covering it with a plastic sheet which traps the heat inside and prevents dryness.
What Are The Benefits Of Composting Leaves?
- Garden Protection – The composted leaf pile can be used directly in the garden bed, as a top dressing. In the winter, the compost acts as insulation for the garden. During the wetter months, the compost pile protects the garden soil from eroding as rain travels over it. It also keeps the nutrients from being washed away in the rain.
- Container Insulation – Another way to utilize composted leaves is to protect outdoor containers during winter. Composted leaves can be clustered around all sides of the container and will act as insulation.
- Leaf Mold – Composted leaves can be used to create leaf mold, which can be stored for several years and used as needed. Leaf mold slowly decomposes and provides a continuous source of nutrients to plants and soil. It is frequently used as mulch in garden beds. It is highly regarded because of its ability to retain water.