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In the developed world the impervious surface is king. Roads and car parks are sealed with tar macadam, footpaths hard paved and concreted. Buildings are built to be unyielding; roofs made from slate, tile, glass, zinc; materials designed to shed water quickly and efficiently via drains to “somewhere else”.
For the first two months of 2014, much of the British Isles reeled from the impact of a succession of severe storms. Rainfall records were smashed as coastal towns and low-lying inland areas bore the brunt of the battering. The weather may have been freakishly awful but there can be no doubt that the effect of huge volumes of runoff water from our world of impervious surfaces was coming home to roost. The “somewhere else”, it turned out, was right here.
In the midst of the worst, David Cameron, the UK prime minister, pledged £130m of additional funding for flood defence and mitigation works; big engineering to battle nature. Yet, could part of the answer to increased storm water flooding be under our feet, in the form of the garden lawn?
The ornamental lawn has been a feature of European gardens for centuries, but the British – in particular the English – demonstrated an early and enduring penchant for a patch of emerald turf. Until the advent of the mechanical mower, lawns were the ultimate show-off statement; only the wealthy could afford the services of skilled scythemen to keep the sward neatly trimmed. Edwin Beard Budding’s invention of the lawnmower in 1830 intersected with the growth of an affluent middle class and the mid-Victorian surge in building that effectively created swaths of a whole new promised land of well proportioned villas with their own garden plots – suburbia. Within a couple of decades the ornamental lawn was in reach of the aspiring masses. Lawns must have appealed to the Victorian obsession for order and control. There is no doubt that a striped green sward makes an aesthetically pleasing foil for flowering plants. And lawns are not without sensual appeal – who doesn’t love the smell of fresh-cut grass and the feel of cool turf under bare feet?
Over the past 20 years the ubiquity of the ornamental lawn has suffered two significant reverses. An increasing awareness of the environmental responsibly of gardeners, the biodiversity potential of gardens and a more “natural” stylistic approach have led some to question the role of the lawn in the modern garden. After all, as a minimum, a lawn needs mowing, expending precious fossil fuels in the process. A really good lawn will need much more besides, as Robin Lane Fox explained last week; feeding with fertiliser, treatment with moss killer, spraying for broadleaf weed control, spiking, scarifying, irrigating. Lawn extremists may even be tempted to douse the ground with earthworm killer, lest those pesky worm casts spoil the neat surface. At the other end of the spectrum the fake lawn, once an object of derision and a source of friction burns, has improved enough in appearance and “feel” to warrant consideration by those looking for a hard-wearing, low-maintenance alternative to the real thing.
But by far the biggest threat to lawns has come from the motor car. About one-third of the 21m homes in the UK with a front garden have been turned into hard-paved parking spaces in the past two decades. The loss is equivalent to 42 Hyde Parks – 14,200 hectares of green, permeable space.
In the US, pavements and other impervious surfaces cover more than 43,000 sq miles, an area almost the size of Ohio. Where environmentally sensitive ecosystems (like the 1.1m- acre Chesapeake Bay watershed) come into the firing line the effects can cause irreparable harm. Storm water runoff is typically poor quality, laden with sediment, pollution and phosphates from agricultural fertilisers. The 400,000 acres of impervious surfaces in Maryland send runoff into Chesapeake with such velocity that the effect is like mini-tsunamis, scouring the ground and sending degraded, damaging water into the bay.
The natural porosity of a lawn allows water to percolate slowly through the sward and soil. Root growth and a healthy earthworm population further improve absorption rates; storm water runoff from a hard surface is 20 times greater than that of a lawn. Studies by the University of Minnesota showed that even on acute gradients, lawns are effective at reducing runoff. In urban areas the dominance of impervious surfaces means that between 40 per cent and 50 per cent of rainfall runs directly into the nearest drain. It doesn’t require a degree in hydrology to work out that in times of severe precipitation there can be only one outcome.
So if lawns are good at absorbing water and slowing down storm water runoff, what about the environmental concerns around them, such as fossil fuel use in maintenance and comparative lack of value to biodiversity? The Biodiversity in Urban Gardens in Sheffield (BUGS) project, conducted by the University of Sheffield, concluded that the city’s domestic lawns produced about 39,000 metric tonnes of clippings for disposal over a 20-week growing (and mowing) season. While much of that ended up in the municipal incinerator it could, with appropriate incentive and investment, be composted – either at source or by the city – or with the appropriate mower mulched back into the sward.
Fuel usage is harder to gauge due to the variability of mower and lawn size, combined with frequency of use. However, even the largest lawns and thirstiest mowers cannot come close to the fuel use of a family car on the school run or weekly shop. Leading lawnmower manufacturers have embraced using lightweight, high-tech materials and efficient fuel technology, resulting in efficient machines full of recycled and recyclable components. Although well-maintained lawns were deemed to be typically sterile environments for garden biodiversity when compared with planted borders or wild meadow areas, the BUGS report cited the scientific evidence that lawns contribute a number of key “ecosystem services”.
Among these was “microclimate modulation”; a lawn can act as an air conditioning unit, reducing air temperature locally as well as surface temperature. The component grass plants photosynthesise just like any other plant, producing oxygen and absorbing carbon dioxide, with a 250 sq metre lawn estimated to produce enough oxygen for a family of four. Lawns also help filter atmospheric pollution and dust particles, and are effective at reducing noise pollution thanks to their capacity to absorb sound waves.
As Britain lay submerged in those early weeks of 2014 the clarion call from flooded shires and suburbs was for more river dredging, bigger sea defences, even the creation of a huge sea lagoon to accept the flood water from the Somerset Levels. The promise of big engineering and big bucks may well make for the right sound bite when the flood waters are rising, but perhaps a better promise would have been to legislate against the proliferation of impervious surfaces. And lay more lawns instead.
Matthew Wilson is managing director of Clifton Nurseries, London