When the leaves start falling, we can spend hours removing them from our lawns. But leaving them where they are is often better for the grass, says James Wong.
IT IS late autumn where I live in London – a time of year that sees millions of gardeners like me, across the northern hemisphere, donning their thickest jumpers and spending hours raking giant piles of leaves into plastic bags at the end of driveways. In the US alone, nearly 10 million tonnes of garden waste go to landfill every year. That is a phenomenal amount of effort, not just from an environmental perspective but frankly from that of our creaking backs, too. So wouldn’t it be great if there was an alternative?
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Strangely, despite it being one of the most deeply ingrained of gardening practices, this seasonal chore makes very little sense ecologically. In natural ecosystems, falling leaves help return minerals essential for healthy plant growth to the soil, and they add organic matter, which greatly improves soil structure. This makes forest soils some of the richest on Earth, as plants continually generate their own fertiliser. Removing leaves year after year breaks this beneficial cycle. So where does this illogical advice come from?
Well, it largely stems from the belief that thick blankets of fallen leaves can choke plants beneath them, especially shorter species like lawn grass, creating a light-excluding layer that shuts down essential photosynthesis. The surprising thing is, this received wisdom has only recently been scientifically scrutinised, with a range of studies all pointing to the exact opposite conclusion.
According to researchers at the University of Wisconsin-Madison, if up to 20 per cent of your lawn is covered by fallen leaves, you might as well go back indoors and put your feet up. The fertility benefits of this light leaf coverage far outweigh the drawbacks – the leaves will quickly break down and help next year’s lawn grow far better than if you had raked them.
Even a much denser coverage of up to 50 per cent still won’t require raking. Instead, the newconsensus is simply to run a lawnmower over your lawn, shredding the leaves into a fine confetti of smaller pieces. These will break down faster and scatter more evenly.
Only at over 50 per cent coverage do the Wisconsin researchers recommend raking, and even then they advise moving the leaves to adjoining borders under larger plants, not off site.
Other studies don’t recommend raking at all, just a once-over with the mower, even for leaf carpets up to a whopping 45 centimetres deep! Save time, carbon and effort, and in exchange get a healthier lawn from free fertiliser you have grown yourself – that seems like a pretty good deal.
And for geeks (like me) wondering how many giant plastic bags could be saved by simply not binning this homegrown fertiliser every year? I weighed a bagful myself to do the (very rough) maths: in the US alone, approximately 700 million.
James Wong is a botanist and science writer, with a particular interest in food crops, conservation and the environment. Trained at the Royal Botanic Gardens, Kew, in London, he shares his tiny flat with more than 500 houseplants. You can follow him on Twitter and Instagram @botanygeek
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