The forest floor is a thick layer of healthy, nutrient-rich soil thanks to the leaves that fall every year. The dense mat of slowly decomposing leaves builds the soil, improves aeration and water retention, makes plant food, and creates a wonderful environment for teeming earthworms and microorganisms. We can replicate this natural process of soil building by adding leaves to our gardens as compost, leaf mould, and mulch. Instead of hauling those leaves away, use them in your garden to improve the health and structure of your soil.
Add leaves to your compost pile, bin, or trench as “brown” or carbon matter to create nitrogen-rich plant food. As a rule of thumb, you want your carbon and nitrogen matter to be balanced about 50:50. Shredding the leaves will keep them from matting and will speed up decomposition, as will turning the pile regularly. Leaf mould is low in nitrogen but unsurpassed in building the soil by adding humus. Leaf mould can also be used with great success in potting mixtures. Fallen leaves can be mulched on your garden about (2-4 inches) deep and can be used around perennials, between rows of vegetables, or as an over-winter soil protector.
Leaves are a free gift of nature given to us every year. As we rake up the leaves every fall, let’s look at how to use leaves to improve the soil in our vegetable gardens by:
- Composting leaves
- Leaf mould
- Mulching with leaves
Leaves are a great carbon source to add to your compost bin or pile. A healthy compost pile is a combination of brown matter and green material. Brown matter is high in usually dead and dry organic waste (such as leaves and straw), while green matter was recently alive and high in nitrogen like kitchen scraps or freshly pulled weeds. Microorganisms in the soil consume the decomposing matter at a rate of 30 parts carbon for every 1 part nitrogen, so you want to have your brown:green ratio balanced for healthy decomposition. Even though the microorganisms need a 30:1 ratio of carbon to nitrogen, this doesn’t mean that you add 30 times as much brown matter as green. You want to mix your browns and greens at a rate of 1:1. Brown matter contains significantly more carbon than nitrogen (in the case of leaves, they have 60 to 80 times more carbon than nitrogen) and because green organic waste contains a fair amount of carbon, too. Here is a great website that goes into detail about the carbon to nitrogen ratio of compost.
The ratio of brown to green matter also affects the temperature of the pile and determines how fast the compost decomposes, and a 1:1 ratio is again ideal. If there is not enough carbon, the compost will become overly wet, matted, and stink of ammonia. If nitrogen is lacking the compost will dry out and not heat up sufficiently resulting in poor decomposition. Freshly fallen leaves contain more nitrogen than old dry leaves.
Compost is an aerobic decomposition, meaning that the microorganisms at work thrive with oxygen so it is important to provide aeration to the pile for proper decomposition. Turning the pile keeps the temperature high and the decomposition process going.
You can make your compost by simply piling everything in a big heap, or you can use a compost bin. Here are a few good and simple ideas for a DIY compost bin.
Here are three ways to successfully compost leaves for your vegetable garden.
If you need help aerating your pile, drill holes in a PVC pipe and insert it into the centre of the pile.
- Shred the leaves. This step isn’t necessary but it will significantly speed up the process. The easiest way is to run a lawnmower over your leaves (attach a mower bag if possible), but you can also buy small leaf shredders. You can also shred leaves with a weed eater in a garbage can.
- Fill your compost bin alternating leaves (and other brown matter) with green organic waste at a 1:1 ratio.
- Turn the compost at least once a month, but turning the pile every week will accelerate the decomposition.
- Apply to the garden. Your leaf compost will be ready when it is sweet-smelling, fluffy, and dark. It is always a pleasure to handle the fresh, rich humus that comes from a compost bin. This can take between 6 weeks to 6 months depending on your turning schedule, the composition, and even the weather. Use it as a top dress or dig it into your soil.
This is made the same as hot compost, except you don’t turn the pile. If you are anything like us, turning the compost doesn’t always make it to the top of the “To-Do List” and the compost pile slowly dwindles down on its own. Cold composting takes relatively no work, but there are a few disadvantages:
- It can take a year or two before the compost is ready to use.
- During this time, a lot of the nutrients can leach out of the compost and be lost in the soil under your compost bins.
- Depending on what you put in your pile, it can either become a rotten mess or dry out and mould.
All that aside, cold compost is far better than no compost at all. We have had great success with cold composting throughout the years. If you do not have time to turn your compost bins, consider getting a pig!
Perhaps my favorite way to compost is trench composting, and leaves work very well for this method, too. The idea of trench composting is to dig your compost directly into the garden and let it slowly rot underground.
- Shred the leaves. Again, this step isn’t necessary but it will help speed up the decomposition process. Run your lawnmower over the leaves or use a commercial leaf shredder.
- Dig a trench. You can prepare a long trench if you want to compost a lot at one time, or you can dig a small hole as needed. Dig the trench beside your growing vegetables, as you don’t want to plant directly over the compost as it can cause the roots to rot along with the compost.
- Put in your leaves and other organic waste into the bottom of the trench at a brown:green ratio of 1:1. When trench composting leaves, it is better to add more green matter rather than less.
- Bury the leaves and other matter by filling the trench back up with soil. The trench can be slightly mounded as it will sink as the leaves and other matter breaks down.
Now your compost is directly feeding your vegetables and improving your soil. Here is an article that goes into a bit more detail about trench composting.
Can I Mix Freshly Fallen Leaves Right into My Garden? In small quantities, digging leaves directly into your garden is fine since they will slowly break down in the soil and create humus and food for your plants. Adding large quantities of leaves, however, is not recommended. Remember that the microorganisms responsible for decomposing the leaves consume 1 part of nitrogen for every 30 parts of carbon, yet dry leaves contain nearly 80 times as much carbon as nitrogen. The microorganisms will consume the nitrogen in your soil to make up for the insufficiency and your soil can become depleted of this essential element. Some people refer to this by saying the leaves “tie up nitrogen” in the soil.
Leaf mould is perhaps the best way to add humus to your garden. Though the name sounds like something unpleasant, the mould refers to the fungi that cause this extremely beneficial process.
Leaf mould is an anaerobic decomposition and uses different microorganisms than compost. The microorganisms involved in making leaf mould do not require oxygen but instead thrive on nitrogen. Because of this, leaf mould is a superior source of humus but it is not a food source for your plants. Leaf mould benefits your garden soil by improving soil structure, aeration, water retention, and loosening the soil. Leaf mould also works great in potting mixes in place of peat moss.
A Natural Replacement for Peat Moss Peat moss is a common soil amendment, especially in potting mixtures. However there are many environmental concerns over harvesting peat moss and the reality is that peat bogs that are thousands of years old are stripped in very destructive ways. Leaf mould is a fantastic replacement for peat moss that is sustainable, regenerative, and environmentally sound.
Leaf mould may take a year or two to decompose, but it is very easy to make. Here are a few different ways to make leaf mould for your vegetable garden:
Leaf Mould Pile
- Gather leaves.
- Put the leaves in a pile. In lieu of a pile, you can make a small cage with a few posts wrapped with chicken wire. Pack the leaves into the cage.
- Wait. Leave the pile undisturbed for a year or two, and the leaf pile will have turned into very good quality humus.
Making Leaf Mould In A Garbage Bag
You can also make leaf mould in a large plastic garbage bag. This process is faster than making it in a pile, usually taking about 6 months to fully decompose, but you have to consider the potential downsides of introducing plastic into your vegetable garden.
- Shred the leaves. Not necessary, but running over your leaves with a lawns mower first will help them break down faster.
- Fill a large garbage bag with leaves.
- Moisten the leaves lightly and tie the bag shut.
- Cut a few holes or slits in the bag to allow airflow.
- Turn the leaf mould every week or so by shaking or rolling the bag.
- Moisten the leaves as needed. Every month or so, it might be necessary to add a bit more water to keep the leaves damp.
- Add to your garden in about 6 months or so when the leaf mold is fully decomposed.
Mulching With Leaves
Leaves make an excellent mulch or top dressing for your garden. Leaf mulch will choke out weeds, retain moisture, maintain soil temperature, and keep the soil from eroding over winter.
While tilling leaves directly into the garden can deplete the soil of nitrogen, this is not a concern with mulched leaves. Leaves that are used as a top dress will slowly break down and become incorporated into the garden at a rate which the soil can naturally handle.
Apply about 5 to 10 cm (2-4 inches) of leaves to your garden bed. They can be put on pathways, between rows of vegetables, or around perennials. When mulching around plants, do not put the leaves right up to the plant as they can make the soil too moist and the plants can rot. You can either shred leaves or leave them whole. Shredded leaves will break down and enrich the soil faster, while whole leaves will suppress weeds and retain moisture better.
Best Leaves For the Garden
All leaves are not created equal, and some leaves are better to use in your garden. All leaves naturally contain lignin which inhibits decomposition and leaves that have a lower lignin content will break down faster such as poplar, maple, ash, fruit tree leaves, and willow.
Leaves from oak, birch, holly, beech, and sweet chestnut have more lignin and will take longer to break down but they are still excellent additions to the vegetable garden.
Leaves to Avoid
Do not use Black Walnut or eucalyptus leaves as they contain a naturally occurring herbicide that inhibits growth in your garden.
Leaves and Soil Acidity
Fresh leaves usually have a pH lower than 6.0 and can make soil more acidic (lower the pH). However, as the leaves break down into leaf mould, or turn into compost, they become almost neutral.
Over time, leaf mould will help neutralize the soil whether it is acidic or alkaline.
If you are using leaves to replace moss, remember that most peat moss has a neutral pH, while Canadian sphagnum moss has an acidic pH of 3.0 to 4.5
Trees for the Garden
As a child, my mental image of a vegetable garden was a plot interwoven with veggies, trees, fruits, and flowers that was as beautiful as it was practical. However, when I planned my first ¾ acre garden, this image was somehow replaced by a flat field of vegetables with maybe a few fruit trees pushed the outer extremities.
The modern perception of a vegetable garden is row upon row of vegetables, but this horizontal view of the garden neglects to incorporate the 3-dimensional aspect of nature. We are often made to think that trees in the garden will block valuable sunlight from reaching our vegetables, yet plants that need “full sun” will thrive with 6 to 8 hours of sunlight each day, and the rest of the time they can take a break underneath the branches of a tree.
Incorporating trees into our gardens not only makes use of “unusable” space, but it breaks up the monotony of monocropping, reduces erosion, improves water retention, creates biodiversity, and also puts a valuable source of soil fertility right in front of us. Or in the case of the leaves, right over our heads.
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.
© 2021 Bellwether Farming
Bellwether Farming (author) from Alberta, Canada on August 31, 2021:
This is a very good point, Cristina Vanthul. We should do everything we can to support vital pollinators.
Bellwether Farming (author) from Alberta, Canada on August 31, 2021:
Keep up the good work, Maren Elizabeth Morgan!
Maren Elizabeth Morgan from Pennsylvania on August 30, 2021:
I've been doing this for years. My "unwoke" neighbors don't get it. But, I carry on!!!
Cristina Vanthul from Florida on August 29, 2021:
I don't have a lot of trees that drop their leaves. Those I do have, I tend to just leave the leaves in place. First, they act as mulch and compost for the trees. Second, many of our bees and other insects are solitary and ground-dwellers. They'll use the leaves and rotted branches as homes and nests. If you can't leave all the leaves, forego a small area so that your pollinators have a place to call home.