Garden Management Challenges and Opportunities
Garden management in a warmer world will present a range of challenges and opportunities.
The following are some examples highlighted in the report:
Drought
A warmer climate will lead to the introduction of new and exciting species into gardens but it will also threaten the traditional English cottage garden. Herbaceous border species such as aster, delphinium, lupin and phlox requiring deeply cultivated, fertile, moisture-retentive soil will not adapt well to drier summers and will need more intensive care.
Peak garden demand for water will occur when least available in summer drought and in the more densely populated South East, where the lowest ground water reserves will be available. Managing rainwater run-off will be of crucial importance, as will water conservation measures such as soil mulching and harvesting rainwater.
Certain species, such as beech, are very sensitive to drought and the effects of prolonged dry summers on native woodlands, such as the Ashridge Estate in Hertfordshire, could be particularly severe. Other species, such as Verbena bonariensis, thrive in dry conditions and the Dry Garden at RHS Garden Hyde Hall in Essex shows gardeners how to cope with drought.
Flooding
Prolonged waterlogging weakens and kills tree roots. Cedars at the National Trust garden Osterley Park in Middlesex and plants in other gardens have already been affected by flooding. This can be avoided by installing and improving drainage in large gardens but is much more difficult to control effectively in confined domestic gardens. Some of the exciting new species that could be introduced are intolerant of winter weather and will need careful management to survive.
Heavier winter rain may increase periods when the soil is waterlogged and airless; it may also arrive at higher rates leading to erosion and flooding. Run-off from hard landscaping and roofs of garden structures may be more than current methods of disposal can cope with.
Sufficient storage to keep enough of this water for all summer shortages will be too expensive and consume too much space to be an option for most gardens, but equally, most gardens could store much more water than they do at present. Careful management of the soil to increase rooting depths and moisture-holding properties may also conserve a significant amount of water.
Excess water will have to be led away. However, gardens commonly have nowhere for water to go, as they seldom have access to ditches or drains. This could lead to frequent localised water logging and even flooding, unless community wide drainage schemes can be implemented.
Where flooding is less severe gardeners can improve the chances of their plants surviving by investing in raised beds, choosing plants that are less likely to be damaged by prolonged wet and improving water flow through the soil by incorporating gravel and organic matter into the soil.
Erosion affects bare soil on slopes and can be prevented by close planting with subjects whose roots bind the soil, and in severe cases by terracing. Mulches are likely to be swept away in some situations and here, dense planting or mulching with heavier materials such as pebbles can help.
Mulching helps to conserve summer moisture, and also helps roots survive wet winter soil. There is evidence, from RHS Garden Rosemoor in Devon, that mulches provide a well-drained environment for roots above the sodden soil.
Mulching will also help weed control - milder winters may promote weed growth, and these will be especially hard to deal with when the soil is too wet to work.
Containers are likely to need more open composts if their contents are to avoid lethal winter waterlogging. This may make them more prone to summer droughts. An alternative may be to invest in covered areas that shed rain, but allow in light, to over-winter containers.
Warmer winters
Fine lawns - the icon of British gardens - are high maintenance features that are particularly suited to our current mild and moist climate. The forecast of a longer growing season may well demand year-round mowing and lawn care, raising maintenance costs in large gardens. In the future, lawns may have to consist of coarser, drought-resistant grasses that can cope with drought and reduce the need for irrigation.
Some plants e.g. cherries and blackberries, which require chilling over winter to stimulate flower buds, could suffer from warmer winters. This is a concern for the British fruit industry as well as domestic gardeners.
Warmer, wetter winter weather will increase the susceptibility of plants to diseases. Some pests that are normally dormant in winter may remain active and so damage vulnerable plants earlier in the year. There is great potential for fungal damage to plants that form key structural elements in the formal planting of heritage gardens, including yew, box and holly. For example, wetter, warmer winters will favour the spread of water-transmitted diseases such as Phytophthora species, which has already affected the yews at Westbury Court, a rare survival of a 17th century Dutch-style water garden in the Severn floodplain in SW Gloucestershire.
The RHS Advisory Service at RHS Garden Wisley has noticed an increase in the number of enquiries about climate change related pests and diseases. Several new-to-Britain pests such as the rosemary beetle, berberis sawfly and the lily beetle are now established in Britain. They are spreading more widely due to a warmer climate. New plant diseases will become more prevalent e.g camellia petal blight will be widespread in Spring 2003 due to its rapid spread through southern England last year. Existing plant pests and diseases may become more prevalent due to the favourable growing conditions of warmer, wetter winters.