Nature’s ‘wake-up call’ in the garden Print E-mail
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Water-logging and drought

Potentially one of the most serious effects of climate change is on soils. The report concludes that managing changes in soil water and nutrients represents one of the biggest challenges for 21st-century gardeners.

Increased temperatures will speed up the biological activity of soil micro-organisms. This will break down organic matter more rapidly, releasing nutrients more quickly. In the short-term, faster and more vigorous plant growth is likely to result, but nutrients will be lost more rapidly from the soil as they are washed away (leached) in winter rains.

Evidence suggests that nitrate losses from soils may double. Maintaining soil fertility by replacing organic matter will be essential, the report concludes. Higher winter rainfall will exacerbate leaching and is also likely to cause more soil compaction and erosion.

Summer droughts will become ever more common, particularly in the South East, an area that already has a high population and low water reserves. Higher temperatures also increase evaporation from the soil - by as much as 30 per cent per 3°C (5.4°F) increase.

On the other hand, winter water-logging is predicted to increase in frequency. In large gardens, drains and ditching may help, but water-logging is much more difficult to control in tightly-packed suburban gardens.

Warmer gardening

The report stresses that not all of these are changes for the worse - at the least, global warming should increase the range of plants gardeners can grow outdoors all year round, wherever they live. As the report puts it, "Tresco has spread to Tunbridge Wells and is on its way to Teeside."

About 85 per cent of the garden plants in cultivation in the UK originate from warmer climates than our own and even slightly higher winter temperatures will reduce frost damage to marginally hardy species such as Abutilon, Callistemon species (bottlebrushes) and Osteospermum over much of the country.

Frosts are unlikely to disappear, but will become much less common in many areas, although the precocious plant growth that our warmer springs are already encouraging will remain vulnerable to sudden cold snaps.

Summer drought is perhaps one of the greatest problems climate change is likely to pose gardeners. Even short periods of hot, dry weather coupled with more limited water resources can kill many annuals and perennials and may also weaken perennials and trees so they are less able to cope with pests, diseases and winter water-logging.

Gardeners in areas with summer water shortages can plant drought-tolerant species but may then face problems nursing such plants through winters, during which soils might remain waterlogged for long periods, rotting the plants' roots and making them vulnerable to waterborne diseases. 

Garden character

The extent to which the character and styles of our gardens will change depends on their existing character, on regional climate now and in the future, and on cultural changes including gardening fashions. There is likely to be the most resistance to change among 'heritage' gardens preserved for their style and contributions to British gardening history; but it will become increasingly difficult and expensive, if not totally unsustainable, to maintain their existing character and planting combinations once warming starts to be pronounced.

By contrast, the report states, in contemporary domestic gardens, "climate change offers exciting opportunities," especially to gardeners in the northern UK. The recent trend for borderline hardy subtropical and Mediterranean species is likely to continue and ultimately even Banksia and Protea species might be grown outdoors.

However problems may arise with growing cultivars of top and soft fruit that require a time of winter chilling below fixed temperatures to initiate flower buds. Certain bulb species too, such as hyacinths, need low temperatures to stimulate root development.

Longer, warmer summers mean annual species will complete their lifecycles earlier, and possibly die back before the end of summer. Conceivably gardeners at the end of the century may have to plant three displays of annual bedding a year, for spring, early summer and late-summer-into-autumn.

Perhaps one of the most threatened garden features is that icon of the English garden, the fine-sward lawn. Drier summers will increase browning and the cost of increased irrigation will escalate - if irrigation water is even available. More money and time will have to be spent on mowing all year round, as well as addressing compaction and moss growth caused in wetter winters.

For summer lawns, coarser, more drought-tolerant grass species are likely to perform better, but, as with other species from drier parts of the world, there may be problems with wetter winters. More drought-tolerant, lower maintenance meadow-land may become increasingly attractive options, particularly in large areas.

Challenges and opportunities

The report concludes that although climate change will enable British gardeners to grow a wider range of species, to increase the yield of some vegetables and fruit and to allow crops such as grapes and kiwi fruit to be grown further north, it will also bring major challenges. Gardeners will need to manage drier soils in summer and wetter soils in winter. They will have to work harder to maintain soil fertility.

They face an intensification of pest, disease and weed problems. And they will need to find more time for the increased maintenance that comes with a longer growing season and more rapid growth rates. Storm and flood damage is likely to become more frequent and summer water supplies will be more difficult and expensive to obtain.

"While the challenge for many gardeners may be the introduction of new and exciting species into their gardens, as the climate progressively becomes warmer, a much greater challenge to gardeners will be to create the traditional English cottage garden," say Bisgrove and Hadley.

Their report also highlights the need for further research to improve the mathematical models used to predict climate change; to investigate its likely impact on garden plants and styles; to identify species better suited to warmer, drier gardens; and how to improve soil management and water conservation.

Our climate is shifting and the rate of change seems set to accelerate. Its effects will impact on many aspects of our lives, but perhaps nowhere as noticeably as in the garden. Many aspects of the art and craft of horticulture will have to adapt to a changing world, as attempting to continue with traditional plants and garden styles is likely to prove increasingly difficult and expensive. Working with the new conditions by using species better adapted to them will almost certainly be a more viable option.

The report was summarised by Phil Gates and Jon Ardle. This edited version is reprinted with kind permission of The Garden, magazine of the RHS.
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