Why do we rake leaves at all?
In addition to aesthetic considerations, raking leaves for the winter has several important functions. First and foremost – leaves left on the lawns can land in sewage drains and clog them. This in turn results in flooded streets or buildings. It’s not difficult to imagine such a situation – even in a medium-sized city, several hundred tons of leaves may fall in autumn. If moved with the wind to the sidewalk or street, they can pose a threat to pedestrians, bicycles and cars. It’s really easy to slip on wet leaves.
In addition, one of the strongest arguments for raking leaves is that dead plant tissues in such amounts rot intensively. This aesthetic problem is revealed in spring, when snow melts and the putrefaction processes intensify. As a result, instead of green grass, for some time, we have leafy mud in the urban space.
Rotting leaves – healthy soil
Such “mud”, as it turns out, despite dubious aesthetics, is very essential for nature. Forests are a good example of how many advantages can a layer of plant organic matter bring to soil. In such natural ecosystems, dead parts of plants (mainly leaves) form an organic layer. It’s thanks to it that the ground in deciduous forests is so rich in nutrients. Decaying leaves are a great, natural fertilizer – and not just in the forests. Boston University researchers have found  that along with leaves, about 1/3 of the nitrogen needed by urban trees is removed from Boston’s suburbs every year. Not raking leaves for the winter could potentially reduce the need for fertilizers by half.
The decomposition of leaves and twigs into organic and mineral compounds is, in turn, the driving force of soil biodiversity. Insects and worms, bacteria, as well as plant roots and related fungi work there together. This facilitates the formation of macropores in the soil. Thanks to them, water freely penetrates into the deeper layers, which prevents flooding, reduces erosion speed and promotes water retention for plant use . In cities that face periodic floods, solutions that mimic the forest’s organic layer can be beneficial.
Biodiversity builds urban ecosystems
Many small invertebrates – e.g. earthworms, beetles, spiders and snails – appear along with the decomposition of organic matter. They are an important source of food for birds and amphibians. Not to mention amphibians love the cool and humid environment that autumn leaves provide. Hedgehogs also benefit greatly from the fallen leaves. In winter they provide shelter for safe hibernation, and in autumn and spring a rich food base (hedgehogs are insectivores). In autumn, when they need to accumulate energy reserves for safe hibernation, and in spring, when they need to catch up shortly after waking up, a richly set buffet will definitely be helpful.
Raking leaves for the winter therefore significantly impoverishes our urban biodiversity enclaves. And it’s particularly important. It’s recognized that the level of biodiversity in the ecosystem indicates how healthy and stable is the ecosystem itself . According to this logic, leaving the leaf layer in private gardens or city parks is a big step forward in building healthy urban ecosystems. Leaves provide food base and shelter for their inhabitants, and let us, people, observe the vibrant nature – without leaving the city.
Raking leaves for the winter improves water quality?
Where there is a vote for, there is always a vote against. Some scientists point out that raking leaves for the winter is necessary to prevent the excess amounts of phosphorus and nitrogen from getting into water reservoirs . Indeed, the decomposition of plant organic matter results in these two elements getting into the ground and then, along with rainwater, into rivers. There, in turn, they can lead to eutrophication and, consequently, even dead zones occurance.
On the other hand, blaming autumn leaves seems to be vague. Of course, phosphorus and nitrogen are present in them, but in quantities incomparable to those used industrially. These are elements necessary for plant growth. They are therefore intensively used as fertilizer, e.g. on large-scale agricultural crops. In huge quantities, they also enter rivers along with improperly processed wastewater from industrial farms. Instead of blaming the leaves, it’s better to focus on modern agriculture’s problems.
What to do with litter after raking leaves?
It seems that the benefits of leaving dead leaves in the natural circulation have more benefits than potential harm. It’s worth leaving them at least in selected places of the urban space. However, safety or aesthetic reasons make raking leaves for the winter necessary in some areas. In this case it’s worth considering how to use them in a non-invasive way. There are several solutions which make fallen leaves can a valuable raw material, and not another mountain of waste to be burned or transferred to a landfill.
- First of all (and the easiest) leaves can be composted. The mass resulting from the decomposition of organic matter is a great fertilizer.
- Dead leaves rich in cellulose can be successfully used for paper and cardboard production. Ukraine, for example, implements such an idea for dealing with autumn leaves.
- Research conducted in India and China show that dry leaves can be successfully converted into microporous coal. This in turn works great in the so-called supercapacitors, i.e. energy storage devices.
 Templer P.H., Toll J. W., Hutyra L. R., Raciti S., 2015: Nitrogen and carbon exported from urban areas through removal and export of litterfall. Environmental Pollution, 197, 256-261.
 Muth A. B., 2016: Fallen Leaves? An argument for not raking. PennState College of Agricultural Sciences, Department of Ecosystem Science and Management: https://ecosystems.psu.edu/research/centers/private-forests/news/2016/fallen-leaves-an-argument-for-not-raking [access 09.11.219].
 Lin K., 2012: Seasonal Science: What Lurks in the Leaf Litter? Scientific American, CityScience: https://www.scientificamerican.com/article/bring-science-home-leaf-litter-biodiversity/ [access 09.11.2019].
 Selbig W. R., 2016: Evaluation of leaf removal as a means to reduce nutrient concentrations and loads in urban stormwater. Science of The Total Environment, 571, 124–133.