Should You Use Dead Leaves As Mulch?

Last updated on October 23rd, 2023 at 08:55 pm

In this article, we will talk about mulching with dead leaves: why and how to mulch your vegetable garden with this precious resource that our deciduous trees offer us every year!

We are in autumn.

It is already the end of the beautiful season. That of most vegetables, fruits, flowers, birds singing, and your hands plunged in the warm earth of the vegetable garden!

But the beauty is still there, at every moment, in your garden ablaze with glowing colors.

It is also the time of great preparations, for the next spring, which is already coming soon.

In this period, it is interesting to tuck your vegetable garden (your land) in a big warm quilt, to protect it from winter, by offering a good mulching. A good work will guarantee an energetic awakening of your vegetable garden, in spring, to see you soon, perhaps, bursting with vegetables!

And in autumn, what better way to use what the garden offers? Namely, dead leaves!

Why mulch your vegetable garden (with dead leaves)?

Mulching protects from the cold…
Mulching, installed in the fall, is very important for a good winterization of your garden.

This mulch, to use the analogy at the beginning of the article, is a cover that allows the soil to be protected from the cold during the winter months.

It is in fact an insulating layer, which reduces heat loss from the soil.

Thus, in the depths of winter, your mulched soil will be a few degrees warmer than an unmulched soil, under the same environmental conditions. It will also be more protected from frost.

This will allow the soil life to maintain a higher level of activity, and work itself more easily. This feeds the beginning of a virtuous circle (the decomposition of organic matter in the soil (by this soil life) is faster, which increases the richness of the soil, etc…).

Mulching around perennials or the feet of young trees also helps protect their root systems from the cold.

… And other advantages!
But the autumn mulching of the soil of a vegetable garden (or of the soil of vegetable containers) does not have for only benefit this insulating cover. It also allows :

• To limit the leaching of mineral elements from the soil by rain. The presence of these minerals in the soil is essential for the good future development of the plants, in spring. We talked about this in issue 3 of our digital magazine.
• Increase the soil moisture content. This is very interesting during dry winters, and favors the development of fungal and microbial life (which like moist environments).
• To bring decomposable organic matter to the soil: essential to the enrichment of the latter.
• To limit the germination of weeds: which will avoid you, in spring, to carry out potential weeding. For perennials and young trees, mulching around the feet (for young trees) or plants (for perennials) has the advantage, by reducing the growth of weeds, of limiting direct competition for soil nutrients and water. This favors the development of these perennials or young trees.

• To protect soil life from direct sunlight. Ultraviolet rays, contained in the spectrum of natural (sun) light, are unfavorable to the development of fungal and bacterial life. This direct solar radiation would also tend to make the soil harder and more compact.
• To promote the development of soil life: hiding places, protection…

Advantages common to all mulches
All types of classic mulches allow to implement these benefits. But in this article we will discuss the particular case of autumn mulching with dead leaves. Thus, we will see the benefits of a mulching with dead leaves, in the fourth part of this article! 😉

The characteristics of a dead leaves mulch
The C/N ratio of fallen leaves
An ideal mulch has a balanced C/N ratio (carbon to nitrogen ratio): that is, between 25 and 30. We saw this in our article on mulch production.

A balanced mulch is important so that the soil’s decomposing micro-organisms can gradually break down this organic matter (i.e. decompose the mulch in question), without mobilizing the soil’s nitrogen for this purpose.

Yes, because decomposing organisms need nitrogen to decompose carbonaceous organic matter.

The more carbonaceous the material in question (high C/N), the more nitrogen the decomposing organisms will need to complete the decomposition process.

For balanced organic matter (C/N ratio between 25 and 30, if you have followed me), the micro-organisms find the necessary nitrogen in this matter.

For carbonaceous organic matter (high C/N ratio), the nitrogen contained in this matter is not enough for the micro-organisms to carry out the decomposition process.

So what will they do?

Well, they will take nitrogen from where they find it: in your soil (but also in the air, thanks to the azotobacter!).

Winter mulches that contain too much carbon can, in this way, lower the nitrogen level of your soil during the winter. This could cause nitrogen deficiencies for your plants later in the spring. This is the nitrogen starvation mechanism.

Hence the importance of a balanced C/N ratio mulch.

Be careful though, because it’s actually a little more complicated. The C/N ratio of an organic matter decreases as it decomposes. In particular thanks to the azotobacter which come to enrich it in nitrogen.

Moreover, nitrogen deficiencies generally appear on the surface of the soil (where decomposition takes place) much more than at depth.

It can therefore be more of a hindrance to germination and young shoots, with superficial roots, than for perennial plants with deep roots.

The question that quickly comes to mind is: what is the C/N ratio of the dead leaves that we want to use as mulch?

Different types of leaf litter
The answer is not unique, as tree leaves have a different C/N ratio depending on their type.

That said, all dead leaves are of the “balanced” to “carbonaceous” type

Green leaves, on the other hand, are primarily nitrogenous. With the arrival of low temperatures, the cycle of each leaf stops: proteins (molecules rich in nitrogen), which are used for the functioning of the “living”, are no longer useful and are transformed into carbohydrates. These carbohydrates are then evacuated and stored in the living part of the wood of the plant or tree in question. This leakage of proteins from the leaf therefore increases the C/N ratio of the leaf.

This is why green leaves are nitrogenous, while dead leaves (orange-brown) are more carbonous!

But this carbon ratio in the dead leaf is not the same for all leaves.

Let’s explore this point together, so that we can determine the ideal composition of your dead leaf mulch!

Carbonaceous dead leaves:
Thick or tough leaves (plane, oak, or beech leaves, for example), are generally rich in carbon. (C/N ratio between 50 and 60).

This makes them slower to decompose, and requires the micro-organisms to draw nitrogen from the soil and the air (until a certain stage of decomposition where the nitrogen will be redistributed with the death of the decomposing micro-organisms, but also their secretions).

There are also dead leaves with a balanced C/N ratio.

Balanced leaf litter:

The dead leaves of fruit trees (but more generally the dead leaves with soft and fine appearance) are, in general, balanced concerning their C/N ratio. (this one is between 25 and 30)

They decompose faster than carbonaceous dead leaves. But above all, they will not incite the decomposers to draw the available nitrogen to start their decomposition. Goodbye to potential nitrogen hunger!

Mulching with dead walnut leaves

The leaves of walnut trees are little or not toxic! But this will depend on the species of walnut and its juglone content.

This is the “toxic” compound secreted by trees in the Juglandaceae family. However, not all species contain the same amount. The species that concentrate the most are the black walnut and the butternut.

Our common walnut trees are sometimes grafted on black walnut trees. Thus, it is possible that they contain juglone in good quantity.

However, our common walnut trees, Juglans regia, contain very little! And under the walnut trees, the seeds germinate without worry…

So, you can definitely use your dead walnut leaves as mulch. If you are unsure, leave your leaves in small piles for part of the winter. The juglone will wash away with the rains and you won’t have to worry about it.

If you want to be even more careful, keep in mind that the main problem with juglone is its anti-sprouting effect. So, you can put these leaves at the feet of perennial plants, already in place.

Also remember that it is the dose that makes the poison! Mixing your walnut leaves with other leaves will dilute the possible residues of juglone…!

You will have understood that walnut leaves can be used as mulch!

Let’s close this parenthesis and get back to our sheep!

Can I mulch with diseased leaves?

You can, absolutely! The diseases of fruit trees in particular are not the same as those faced by vegetable plants. Thus, apple scab will not be transmitted to your tomatoes for example!

The winning combo
So, normally, if you’ve followed me this far, you should be able to tell me, what is the most interesting to put in place, in terms of mulching with dead leaves.

So, you know 😉

Actually, there are two mulching options, that I find interesting:

• A balanced dead leaf mulch (fruit trees…) only.
• Or a mulching of carbonaceous dead leaves mixed with nitrogenous organic matter (kitchen waste, for example: peelings, clippings, …). For aesthetic reasons, you can cover plant waste with dead leaves. We can also, to lower the C/N of our carbonaceous leaves, let them compost a few months before spreading them 😉

These two solutions allow us to obtain a balanced mulching.

Nevertheless, it should be noted that in a living and biologically active soil, mulches of carbonaceous dead leaves do not always create nitrogen hunger. In fact, once the natural cycles have started, the machine is well established! And the soil is sufficiently supplied with nitrogen to satiate the plants and the soil life.

So, don’t hesitate to mulch without questioning… If you feel a hunger for nitrogen in the spring, you can add a handful of dried blood per square meter or urine in the spring, when you transplant your first plants.

“Okay, that’s all great stuff. But what are the advantages of using dead leaves instead of straw?”.

What are the advantages of mulching with dead leaves?

If you have trees in your garden, the question doesn’t even arise! You have dead leaves, which work very well as mulch! Why bother looking for straw?

It is also much more interesting to use a material internal to your system (tree leaves), than to import a mulch external to this system-garden! This in order to have ever more ecological gardening practices.

So there you go, if you have dead leaves in the garden, don’t hesitate 😉

In practice: how to mulch your vegetable garden with dead leaves?

Now that you know a little more about dead leaves and their composition, let’s get practical!

First of all, before mulching, aerate the soil a little with a grelinette if it is compact.

Then, with the whole or shredded dead leaves (shredding is useful for carbonaceous dead leaves, because it facilitates the decomposition process), which you may have mixed with kitchen waste (for carbonaceous leaves, for example), you can generously cover the planters or the vegetable garden.

You can also cover the base of young trees (by making mounds of dead leaves around the base).

That’s it! Your vegetable garden is ready to spend the winter in the warmth, and to wake up vigorous, at the first songs of the birds of spring.

Nevertheless, keep in mind that mulch is an insulator: it slows down the warming of the soil in spring. On some heavy soils, the difference is obvious! For example, some gardeners uncover their soil in spring for early crops. It’s up to you to decide according to your needs and your context.

Finally, a last tip: dead leaves are very volatile. We no longer use them to mulch young seedlings: the latter were constantly covered by leaves at the slightest gust of wind, which limited the emergence of our crops!

Conclusion

Dead leaves are a precious resource!
Do not burn your dead leaves: use them as mulch! They are a treasure, to prepare your vegetable garden for winter. Composted, they turn into a real compost, very interesting for the garden.

Winter mulching is beneficial for the garden

Winter mulching allows to :

• keep the soil relatively warm.
• limit the leaching of mineral elements by rain.
• maintain a good level of humidity.
• limit the growth of weeds.
• create a protection against the sun’s rays,
• and to bring organic matter to the soil, enriching it.

All these benefits bring others, such as the promotion of micro and macro fauna, and the promotion of the presence of auxiliary insects, among others…

Getting a little closer to nature!
The dead leaves, elements produced by the garden system (and thus internal to it), constitute the obvious element of mulching. Especially when you are lucky enough to have some!

To use them as mulch is to perpetuate the natural cycle of wild forest ecosystems, where the place of the tree is central. In particular for the life, the development, even the survival, of the native fauna and flora.

It is preferable to compose with these leaves, or other organic elements (plant waste), to tend towards a balanced mulch in its C / N ratio.

You now know a little more about the use of dead leaves as mulch! If you still have questions, don’t hesitate to ask them in comments.

To go further, here is a video on the subject of dead leaves in the garden, made by Le potager d’Olivier.