The falling leaves drift by my window, the autumn leaves of red and gold.1
As a kid growing up in the Philippines, I remember seeing photos of brilliant Autumn foliage in books and magazines, and often in calendars when October came around. I remember thinking what a dream to experience the magic of Fall.
Fast forward a few decades and I am living in New England, the heart of Fall foliage. It is my favorite season. I love everything about it—the nip in the air, wearing jackets and boots, the tease of the holidays, and yes, the color. My home is surrounded by tall oak trees that have begun shedding their magnificent garb. With the aid of blistery winds this last weekend, they’ve converted what once were my lawn, driveway and foot paths into a plush golden carpet. And the leaves, do I love the leaves?
I posted a photo of my front yard covered with leaves on Facebook with the caption:
“What do I see?
Free mulch. Free fertilizer. Free critter homes. Free gym.”
Someone commented: “I don’t miss raking leaves.”
I get it. For many, leaves are just one more thing to add to a list of chores. But perhaps I can help you see leaves in another light.
Why Leaves Fall
First of, leaves don’t passively “fall.” As the days get shorter and colder, deciduous trees actively push out their leaves by sending messages to abscission cells (note the relation to the word “scissors”) located between the leaf stem and branch, to cut off. If you recall, leaves, through photosynthesis, is how trees make food, requiring water drawn from roots to nourish them. But in winter, water trapped in leaves will freeze and expand, damaging cells which kill leaves. A tree with no leaves won’t survive. It’s pretty much like how we have to shut off garden faucet valves in winter, making sure no water is trapped, to avoid a costly pipe burst.
Knowing why leaves “fall” doesn’t help de-clutter my lawn, but it helps to see that a tree does this to protect herself, which ultimately benefits me, since having her alive and healthy ensures I will continue to receive not only the bounty of her beauty and shade, but all the wonderful benefits trees give, not least of which are clean air and carbon storage.
But even in disrobing, trees leave us gifts with their leaves. How are they gifts? Let me give you five ways.
When I was new to planting, I did not understand what mulch was. I saw them in many gardens—a palette of dyed red or brown bark, dotted with a few plants. I thought it was just an American aesthetic.
Mulch can be made from a variety of materials: wood chips, straw, leaves, stones, gravel, even plastic. But while mulch can trim up a garden nicely, its benefits are mostly for its abilities to absorb water, prevent soil erosion, protect plants from temperature extremes and suppress weeds. If you are using organic materials that break down easily like straw, wood bark or leaves (NOT stones or plastic), then you have the added benefit of providing food for the denizens of the underground: bacteria, fungi, protozoa, nematodes, earthworms, and arthropods. In other words, you are providing a feast for the soil web. Organic mulch is future compost. And we all know that compost is necessary for healthy soil and therefore, healthy plants.
So how do I use leaves as mulch in my garden?
For bushes and trees, I tend to just rake or blow leaves to their bases where fellow leaves are already gathered, partially sheltered from winds. It’s like a party in there! But for garden beds I want neat, I shred leaves to top and then water them—or better yet, just mulch before the rains. Once wet, the matted leaves will keep from blowing in the wind. In addition, shredded leaves break down faster than their whole counterparts, so in no time at all, they’ll become compost. Come Spring, I’ll layer black bark mulch (for aesthetics) over the decomposing shredded leaves, which in a year or so will also become compost. Voila! A water-retentive and self-sustaining system that creates healthy soil for healthy plants.
When mulching, be careful not to be heavy-handed in areas where you want seeds to pop up, such as with self-seeding annuals or on lawns. If they can smother weeds, they can smother grass and other small seedlings as well.
Note: while most leaf litter from deciduous trees are great as mulch, soil amendment or in compost, avoid leaves from allelopathic bushes and trees (e.g. Black walnut, Tree of heaven, Fragrant sumac) which suppress plant growth.2
So we know leaves become compost. In truth, most everything except plastic will break down and therefore becomes compost at some point. You and I will also become compost one day. Compost is a broad term that describes organic matter in varying stages of decomposition. Kitchen food scraps we collect in compost bins are compost. So are the leaves and spent flowers that I add into them. These are unfinished compost.
What you buy in nurseries, the one that looks like rich soil, is finished compost. That’s what happens when organic matter has fully decomposed: you get rich, dark crumbly earth teeming with nutrients. Black gold. But that’s not fertilizer per se. Not yet, that is. Though compost contains everything a plant needs, including Nitrogen, Phosphorus and Potassium, the three macronutrients that is the NPK of fertilizers, only a small amount is immediately available as plant food. Soil microbes still have to consume and transform compost nutrients so that they’re bioavailable to plants. Though there are many benefits to compost including improving soil structure and water retention, it’s really food for the soil organisms at this point.
So the difference between compost and fertilizers is a matter of:
concentration -fertilizers have higher concentrations of NPK
origin - fertilizers can be synthetic, and
time - fertilizers are immediate plant food. Compost is slow-release.
If you have been regularly integrating compost into your beds, than the plant food in your soil has been accumulating over the years which reduces or eliminates the need for fertilizer amendments.
What about leaves? While I’ve known that leaves are an important component of compost bins because of their high carbon content, it wasn’t until recently that I learned that by themselves, they also contain NPK and a whole lot of nutrients that feed soil organisms. Like finished compost, the NPK values are small and released slowly, but as they decompose, these are made available to plants. Further, according to a report by Rutgers University in New Jersey, field experiments conducted in Quakertown silt loam soil showed that 17% of the organic carbon in the leaves remained in the soil3 after one year, a plus towards keeping carbon in the ground. So leaves, like compost, are a slow-release fertilizer.
Why is this important? When nitrogen is released too quickly, such as with synthetic chemical fertilizers, any excess that plants don’t consume can contaminate our water system; if exposed to air, it turns into nitrous oxide, a greenhouse gas which warms the atmosphere 300 times more than carbon dioxide.
Free homes for critters
According to the National Wildlife Federation:
A leaf layer several inches deep is a natural thing in any area where trees naturally grow. Many wildlife species live in or rely on the leaf layer to find food and other habitat, including salamanders, chipmunks, box turtles, toads, shrews, earthworms, and many insects’ species.
In addition, several butterfly and moth species overwinter as pupae in leaf litter. Besides encouraging pollinators in the garden, they are also an important food source for other critters, especially birds in spring which need caterpillars to feed their young.
Free amendments to hugelkultur and core garden beds
Hugelkultur, German for “mound culture” is the ultimate raised bed where branches and twigs, organic material and manure4 are piled into a mound, soaked with water and then topped with soil, ready to be planted on. Over time, not only do the organic components slowly break down to provide nutrients to soil, but the air pockets created by the components even when they decompose, trap moisture, reducing the need to water. In addition, the decomposing organic matter in hugelkultur beds raises the temperature just enough to boost plant growth.5
While large hugel beds piled high—as much as 7 ft. tall, and utilizing large logs that will take many years to break down guarantee long-lasting fertility, it’s not a practical solution in home gardens. To preserve aesthetics in my yard, my solution was to dig 2 feet deep to bury branches, twigs, leaves, compost and manure, soak with water, then pile on the soil. Even if my pile was 5 ft. tall, the visible mound was only 3 ft. high. I have since created over 2 dozen hugelkultur beds over several years, rehabilitating soil so inhospitable even weeds didn’t dare grow. Today, with minimal watering, plants are thriving in formerly barren pockets of our yard.
Core gardening is a planting system I recently learned about from a MIGardener Youtube video. The basic idea is to bury and soak straw (I use shredded leaves) in the center of your planting bed. Like a hugelkultur, the core acts as a sponge that retains water. And of course, the decaying matter will also provide nutrients for the beds. This is much easier to make than a hugelkultur, but it won’t last as long.
There are other planting systems (like lasagna gardening) which employ the same idea of burying organic matter for soil fertility and water absorption. Any planting system that uses organic matter is a great use of leaves. I like hugelkultur beds because I have access to copious amounts of branches and leaves and because they last a long time. But there’s no reason why you can’t experiment and play around with hybrid versions based on resources you have or labor you’re willing to invest.
And now we come to the final gift the leaves give us.
The garden is an outdoor gym. Fresh air and exercise, free, courtesy of leaves.
So to answer my earlier question, do I love the leaves? Yes, I do, let me count the ways…
Compost nutrients: https://www.calrecycle.ca.gov/organics/farming/analyses
Allelopathic plants : https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5988857/
Leaves from City Shade Trees Benefit Soils: https://sustainable-farming.rutgers.edu/wp-content/uploads/2014/09/Leaves_Fr_City_Shade-Trees_Soil_Benefit_Heckman.pdf
Autumn Leaves music and lyrics by Joseph Kosma, Jacques Prevert, Johnny Mercemjr
You can use allelopathic leaves as mulch for the plants and trees they’re from since they are used to their own chemicals.
Organisms that break down matter require nitrogen which can compete with plant needs, so the addition of manure or other nitrogen component to hugel beds compensates for this; over time, nitrogen locked up in organic matter is released sustaining the needs of both plants and organisms.
Gaia’s Garden: A Guide to Home-scale Permaculture by Toby Hemenway