Urban gardens Gardening - RHS
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Gardening
matters:
Urban
gardens
rhs advisory / leigh hunt
What is the value of gardens Moderating
in urban areas? temperature
Do gardens sustain our cities? Domestic gardens are the equivalent of an
air-conditioning system for our cities. Urban-
garden plants and trees help cool the air in
It is often said that gardens are a vital part of
our towns and cities, yet where is the scientific
Introduction our towns and cities, combating dangerous
proof? To establish the facts, RHS scientists led By Tijana Blanusa, This report, which is a temperatures caused by urban heat waves.
an examination of all the available evidence RHS Scientist summary of that scientific
Trees and hedges can bring heating costs
rhs / paul debois
from published research around the world. review, highlights the
The results, brought together for the first time The UK is an urbanised fundamental role that and energy consumption down in winter by
in this RHS Science Review, have revealed the society: more than domestic gardens play providing shelter and insulation
jon enoch
remarkable depth and range of benefits that 85 percent of the UK in making our cities
gardens provide in urban areas. population lives in towns somewhere we want to
For example, gardens help control urban temperatures, and cities1. Urban domestic live. It looks at the eco Cooling the urban environment
protecting us from extreme heat and cold. They help gardens are a significant system services provided Urban environments are Vegetation has the ability
prevent flooding, provide important habitats for wildlife component of our urban by private gardens and particularly prone to to provide aerial cooling by
and improve human health both psychologically and landscape. They contribute considers their impact, heating due to the shading (primarily trees and
physically. This is why gardening matters. from 22–27 percent of the positive and negative. replacement of vegetated climbing plants) but also
So where next? In a way, this RHS Science Review serves total urban area in many This review points to the areas with dark and through the plant-specific
as a starting point. It provides the evidence why urban cities2, and can represent need to protect our existing impervious surfaces, with process of evapotranspira
gardens should be vigorously protected; pinpoints what nearly half of urban green gardens and ensure their very different thermal tion (water loss through
further research is needed; and highlights the need to space. Domestic gardens provision in urban and radiative properties leaf pores). Current models
encourage good horticultural skills and future generations contain approximately expansion. In addition we (ie pavements and roads predict that a 10 percent
of gardeners. While the RHS is working in many of these 25 percent of the total must support those with absorb considerably more increase in vegetated
areas, everyone – from homeowners to policy makers – non-forest and woodland access to a garden so they heat and reflect surfaces in urban areas
can play their part. For everyone involved in creating and trees3 and can contribute can tend it in a way that considerably less than would help control the rise
maintaining urban gardens, this RHS Science Review as much as 86 percent of continues to enhance planted surfaces – this in summertime air
offers a suite of initial recommendations for action. the total urban tree stock4. urban quality of life. makes them warmer than temperatures due to
I hope you find the following pages of great interest Given the major presence Over the following pages planted surfaces). This climate change4.
and will use the recommendations (back page) and of gardens in our towns and the specific benefits of results in urban air and The fact that urban trees
rhs / paul debois
practical tips to make a difference in the gardens cities, the Royal Horticultural temperature regulation, surface temperature being and other forms of Paved areas absorb more heat and
and green spaces over which you have influence. Indeed Society wanted to under flood prevention, support significantly warmer than vegetation can provide reflect less than planted areas
it is now clear that, as gardens account for almost half stand more about the for biodiversity, and surrounding rural areas, cooling to buildings has
of our urban green space, simple steps carried out at public function that promotion of human the extent of which varies implications for reducing
home really do add up. gardens have in addition health are summarised, as depending on the time of the energy consumption
Sue Biggs, RHS Director General, May 2011 to the personal pleasure are the potential pitfalls of year and specifics of the associated with artificial air Gardens as insulation
we know they bring. For urban gardening. It opens location1. conditioning. Geographical The use of trees, hedges To exploit fully the
that reason the Society, the debate about how Urban heat waves have location, building design and other forms of benefits of planting around
in partnership with the urban domestic gardens the potential to increase and the prevalence and vegetation located houses, care does need to
Universities of Reading can be protected, fatalities due to heat stress2 orientation of trees will all carefully around houses be taken in the design so
and Sheffield, undertook enhanced and exploited to and can increase the affect the extent of can also enhance winter that wind tunnels are not
a literature review of ensure urban quality of life hazards arising from fires savings, but on average energy saving by reducing directed towards the house,
published academic into the future, as well as that occur (for example in summer-cooling energy the speed of air movement and that maximum solar
evidence to examine the offering some first steps Russia during summer savings have been reaching a building (‘wind gain is retained in winter7.
potential impact of that gardeners can take to 2010, 56,000 people are estimated to be around break’) and/or reducing Winter thermal gains are
the domestic garden support the ecosystem of estimated to have died as 30 percent; such savings the temperature difference most significant in cooler
on urban quality of life. their town or city. a result of fire-related smog also help reduce CO2 between existing and (northern) parts of the UK.
and high temperatures3). emissions5. incoming air6.
1 Denham C, White I (1998) Differences in urban and rural Britain. In: Population Trends. UK
Office of National Statistics, pp1–12. 1 Grimmond S (2007) Urbanization and global environmental change: local effects of urban warming. Geographical Journal 173: 83–88.
rhs advisory / leigh hunt
2 Loram A, Tratalos J, Warren PH, Gaston KJ (2007) Urban domestic gardens (X): the extent & 2 Hajat S, Kovats RS, Lachowycz K (2007) Heat-related and cold-related deaths in England and Wales: who is at risk? Occupational and Environmental Medicine 64: 93–100.
structure of the resource in five major cities. Landscape Ecology 22: 601–615. 3 http://cred.be/sites/default/files/PressConference2010.pdf
3 Davies ZG, Fuller RA, Loram A, Irvine KN, Sims V, Gaston KJ (2009) A national scale inventory 4 Gill SE, Handley JF, Ennos AR, Pauleit S (2007) Adapting cities for climate change: the role of green infrastructure. Built Environment 33: 115–133.
of resource provision for biodiversity within domestic gardens. Biological Conservation 142: 5 Akbari H, Kurn DM, Bretz SE, Hanford JW (1997) Peak power and cooling energy savings of shade trees. Energy and Buildings 25: 139–148.
761–771. 6 Meerow AW, Black RJ (2003) Enviroscaping to conserve energy: a guide to microclimate modification. In: Circular EES-43. Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences,
4 McCall A, Doar N (1997) The State of Scottish Greenspace. In: Scot. Nat. Heritage Rev. No. University of Florida, Florida, USA, p10.
88. Edinburgh. 7 Knowles RL (2003) The solar envelope: its meaning for energy and buildings. Energy and Buildings 35: 15–25.
2 www.rhs.org.uk/urbangreening www.rhs.org.uk/urbangreening 3
Preventing Supporting human health
urban flooding Domestic gardens are a ‘public health service’ for our
cities. Gardening eases stress and improves psychological
Urban gardens help keep our cities wellbeing. Gardening encourages sustained exercise and
‘above water’. Garden plants and trees promotes physical health
intercept intense rain, slowing runoff and
Gardening has been incidence of illness or associated with gardening
so reducing the pressure on urban drains. identified as one of the reported illness4; pain can relate directly to
Unlike hard surfaces, the soil in gardens activities associated with relief5, 6; improved improved physical fitness
naturally absorbs rainwater, reducing the wellbeing and enhanced relaxation7; and coping (eg cardiovascular health).
physical health, particularly with trauma8 – as well as Gardening is one of a
risk of flooding in our towns and cities with regard to community unusual indirect effects of number of pastimes that
garden projects. stress reduction such as encourage greater physical
Through the attenuation domestic gardens is Most studies express the reduced crime (ie reduced activity; long-term
of storms and by affecting increasing, especially benefits of natural land domestic violence and engagement with
ground water recharge, through the creation of scapes / green spaces in aggression)9. gardening is often
gardens benefit the urban patios and the paving terms of stress avoidance Furthermore, gardeners achieved because this
environment and help of front gardens to reduce or alleviation; other usually have a large physical activity becomes
prevent flooding1. maintenance and provide psychophysiological element of control over the an outlet for creativity
Mabley Meadow / chris king
Vegetation (especially car parking. benefits recorded have design and management and self-expression10.
trees) capture intense For example, in Leeds included: improved of gardens; this can be The intensity of physical
rainfall and hold rainwater over a 33-year period, Gardens can be cognitive function1; linked with increased activity, however, will vary
temporarily within their there was a 13 percent rich in biodiversity improved self-discipline2; self-esteem, a feeling of with type of gardening
canopy thus reducing increase in impervious alleviation of attention achievement and fulfilment activity, age and ability of
initial flow of rainwater surfaces, 75 percent of deficit disorder symptoms of talent and skill. participant11.
Providing urban
and easing demand on which was due to paving of in children3; reduced Physical health benefits
urban drains2. In addition, residential front gardens;
rhs / Carol Sheppard
vegetation limits flood risk this was linked to higher
by encouraging better
infiltration of water into
the soil, which reduces
frequency and magnitude
of flooding in the area4.
The benefits of vegetated
biodiversity
surface water flows3. front gardens and the Domestic gardens are among Britain’s
1 Smith RM, Thompson K, Hodgson JG,
Despite these advantages, risks associated with key nature reserves. Urban domestic Warren PH, Gaston KJ (2006b) Urban
the area of hard paving in uncontrolled paving of gardens of all sizes support a substantial domestic gardens (IX): Composition and
richness of the vascular plant flora, and
these areas has now been
recognised by the planning range of wildlife. Some animal species are implications for native biodiversity. Biological
Conservation 129: 312–322.
system in the UK; since now more common in cities, particularly 2 Smith RM, Thompson K, Warren PH, Gaston
KJ (2010) Urban domestic gardens (XIII):
October 2008 a planning domestic gardens, than in rural areas Composition of the bryophyte and lichen
RHS / julie henry & debbie bragg
floras, and determinants of species richness.
application has been Biological Conservation 143: 873–882.
required for more than While gardens will never insects, spiders, etc) as 3 Thompson K, Hodgson JG, Smith RM,
5sq m of impermeable replace species-rich, larger, suburban ones4, 5. Warren PH, Gaston KJ (2004) Urban
domestic gardens (III): Composition and
paving5. semi-natural habitats, Furthermore, there is diversity of lawn floras. Journal of Vegetation
they are still a useful growing evidence that Science 15: 373–378.
4 Smith RM, Gaston KJ, Warren PH,
1 Pauleit S, Duhme F (2000) Assessing the complement to such some declining species, Thompson K (2006a) Urban domestic
environmental performance of land cover habitats, and increasingly once common in low- gardens (VIII): environmental correlates of
types for urban planning. Landscape and invertebrate abundance. Biodiversity and
Urban Planning 52: 1–20. provide urban residents intensity farmland, are Conservation 15: 2515–2545. 1 Berman MG, Jonides J, Kaplan S (2008) The Cognitive Benefits of Interacting With Nature. Psychological Science 19: 1207–1212.
2 Xiao Q, McPherson EG (2002) Rainfall with their only close now more abundant 5 Smith RM, Warren PH, Thompson K, 2 Taylor AF, Kuo FE, Sullivan WC (2002) Views of nature and self-discipline: evidence from inner city children. Journal of Environmental Psychology
interception by Santa Monica’s municipal Gaston KJ (2006c) Urban domestic gardens 22: 49–63.
urban forest. Urban Ecosystems 6: 291–302. encounters with the in urban areas, and (VI): environmental correlates of invertebrate 3 Faber Taylor A, Kuo FE, Sullivan WC (2001) Coping with ADD: The Surprising Connection to Green Play Settings. Environment & Behaviour 33: 54–77.
3 Dunne T, Zhang W, Aubry BF (1991) natural world. particularly in domestic species richness. Biodiversity and 4 Moore EO (1981) A prison environment’s effect on health care service demands. Environmental Systems 11: 17–34.
Effects of Rainfall, Vegetation, and Conservation 15: 2415–2438. 5 Diette GB, Lechtzin N, Haponik E, Devrotes A, Rubin HR (2003) Distraction Therapy With Nature Sights and Sounds Reduces Pain During Flexible
Microtopography on Infiltration and Runoff. Neither the typically gardens, eg common 6 Gregory RD, Baillie SR (1998) Large-scale Bronchoscopy – A complementary approach to routine analgesia. Chest 123: 941–948.
Water Resour. Res. 27: 2271–2285. small size of urban gardens frog, song thrush and habitat use of some declining British birds. 6 Ulrich RS (1984) View through a window may influence recovery from surgery. Science 224: 420–421.
4 Perry T, Nawaz R (2008) An investigation Journal of Applied Ecology 35: 785–799. 7 Chang CY, Hammitt WE, Chen PK, Machnik L, Su WC (2008) Psychophysiological responses and restorative values of natural environments in
into the extent and impacts of hard surfacing nor their isolation from hedgehog6, 7. 7 Mason CF (2000) Thrushes now largely Taiwan. Landscape and Urban Planning 85: 79–84.
rhs advisory / leigh hunt
of domestic gardens in an area of Leeds, countryside prevent them One study found that restricted to the built environment in eastern 8 van den Berg AE, Koole SL, van der Wulp NY (2003) Environmental preference and restoration: (How) are they related? Journal of Environmental
United Kingdom. Landscape and Urban England. Diversity and Distributions 6: Psychology 23: 135–146.
Planning 86: 1–13.
supporting biodiversity1, 2, 3. in Sheffield’s domestic 189–194. 9 Kuo FE, Sullivan WC (2001) Environment and crime in the inner city: does vegetation reduce crime? Environment & Behaviour 33: 343–367.
5 Department for Communities and Local Small, city-centre gardens gardens the density of 8 Fuller RA, Tratalos J, Gaston KJ (2009) How 10 Blair D, Giesecke CC, Sherman S (1991) A dietary, social and economic evaluation of the Philadelphia Urban Gardening Project. Journal of
Government, 2009, Guidance on the many birds are there in a city of half a million Nutrition Education 23: 161–167.
Impervious paved areas
permeable surfacing of front gardens,
support similar invertebrate birds is six times that people? Diversity and Distributions 15: 11 Dallosso HM, Morgan K, Bassey EJ, Ebrahim SB, Fentem PH, Arie TH (1988) Levels of customary physical activity among the old and the very old
increase flood risk London, UK. wildlife (such as worms, of the nation as a whole8. 328–337. living at home. Journal of Epidemiology and Community Health 42: 121–127.
4 www.rhs.org.uk/urbangreening www.rhs.org.uk/urbangreening 5
Getting the balance right Conclusions
Domestic gardens must be managed responsibly to ensure they contribute to improved This RHS Science Review summarises
quality of life. There are two main areas of concern: carbon emissions and water use evidence, drawn from published scientific
research from around the world, of the
Carbon emissions Water use contribution gardens and gardening make
Gardens absorb carbon through plant To enable plants and trees to perform their to the urban environment. The breadth
growth and release carbon in death. cooling effect in times of high urban of the information examined has made
Gardening can contribute indirectly to temperature, water is essential. Garden it possible, for the first time, to provide
carbon emissions through the consumption water use is predicted to rise as the effects evidence-based conclusions about the
of manufactured and transported of climate change are felt and as domestic benefits of domestic gardens for the urban
horticultural goods, and through the use of housing stock grows, but water is likely to environment and human wellbeing
power tools for gardening maintenance become more scarce as temperatures rise
The extent to which urban
domestic gardens act as a
in plant production and
transport, manufacture of
The volume of water used
in gardens is strongly
regions of the world
(Mediterranean, Australia)
Key findings from the review
carbon sink or carbon chemicals and equipment, dependent on climate, suggest that, as Beneficial effects Room for
emitter is unclear and and consumption of weather, soil type, style of temperature increases, • Urban garden plants and improvement
there are suggestions that energy in garden garden, and lifestyle the proportion of trees help cool the air in Gardening does have
overall more carbon is maintenance. Activities choices and attitudes. household water used in our towns and cities, some potentially negative
emitted than captured closely associated with the There are no recent data the garden can increase to combating dangerous environmental impacts
through activities related garden also have an available on garden water more than 30 percent6, 7. temperatures caused by and we need to strike the
to gardens and gardening. impact on carbon release use in the UK; the last UK Watering, though, has a heat waves. correct balance in the way
This does depend on (use of plastics, green Government report was significant role, not just in • Trees and hedges can we garden. The issues to
garden style, function and houses, peat, fencing and published 15 years ago5. maintaining the garden, bring heating costs and be aware of are:
rhs advisory / leigh hunt
management, and there garden furniture, barbecue Available estimates but also in maintaining the energy consumption down • gardening can
are steps that gardeners equipment, etc). Perhaps suggest that the proportion cooling effects of planting in winter by providing contribute indirectly to
can take to reduce their most problematic are of household water used in urban areas, and shelter and insulation. carbon emissions through
carbon footprint. lawns which, due to their in gardens will rise to reduction of summertime • Garden plants and trees the consumption of
Gardens, as a form of intensive management almost nine percent in air temperatures in cities. intercept intense rain, manufactured and
green space, represent (fertilisers, powered 2021. This calculation Currently, in times of slowing runoff and so transported horticultural
areas of significant carbon lawnmowing, etc), are only considered the rise in drought, watering of urban reducing the pressure on goods and the use of
flux. At one level they are a carbon costly1, 2. housing stock and growing vegetation including urban drains. power tools; Recommendations
direct carbon sink storing However, some carbon interest in gardening, but gardens is significantly • Unlike hard surfaces, the • garden water use is The findings highlight three areas where change
small amounts of carbon in is stored in garden trees3. not any climate change reduced or fully ceases. soil in gardens naturally predicted to rise over the or further work is needed.
plants, particularly long- In addition, soils are the effects5. Data from warmer absorbs rainwater, reducing coming years, but water is
lived woody species, and
to a greater extent in soils.
They are also a carbon
largest reservoirs of
terrestrial carbon, and soils
in lower-density residential
the risk of flooding in our
towns and cities.
• Urban domestic gardens
likely to become a more
scarce resource. 1 We should all place greater emphasis on protecting
and enhancing gardens and green space in our cities
for the benefit of the environment and future generations.
source: carbon is released urban areas, which contain of all sizes support a These issues, however, can
as plants decompose.
The process of gardening
also contributes indirectly
more gardens, store over
40 percent more carbon
than soils in areas of
substantial range of wildlife.
• Some animal species are
now more common in
be overcome or minimised
by using sustainable
practices (eg choosing
2 Scientific research institutes should build and share
expert knowledge of practices that will maximise the
positive impact of gardens and gardening, with particular
to carbon emissions commercial land use4. cities, and particularly locally sourced and focus on:
through energy consumed domestic gardens, than in perennial plants to • the identification of which trees and other plants are
rural areas. mitigate carbon issues, most suited to providing the optimum cooling effect with
1 Huh KY, Deurer M, Sivakumaran S, McAuliffe K, Bolan NS (2008) Carbon sequestration in urban • Gardening eases planting in spring and minimum water use in domestic gardens;
landscapes: the example of a turfgrass system in New Zealand. Soil Research 46: 610–616. stress and improves autumn when more water • determining the thermal insulating properties of a wide
2 Jo HK, McPherson EG (1995) Carbon storage and flux in urban residential greenspace. Journal of
Environmental Management 45: 109–133. psychological wellbeing. is naturally available, etc). range of plants appropriate for use in domestic gardens;
3 Nowak DJ, Crane DE (2002) Carbon storage and sequestration by urban trees in the USA. • Gardening encourages • understanding the best plant combinations to encourage
Environmental Pollution 116: 381–389.
4 Pouyat R, Groffman P, Yesilonis I, Hernandez L (2002) Soil carbon pools and fluxes in urban sustained exercise and a wide range of garden biodiversity.
ecosystems. Environmental Pollution 116: S107–S118. promotes physical health.
3
5 Herrington P (1996) Climate Change and the Demand for Water. In: HMSO (ed) Stationery Office
Books, p178.
• Gardens absorb carbon Education and training organisations should safeguard
RHS / Jon Enoch
6 Domene E, Sauri D (2006) Urbanisation and Water Consumption: Influencing Factors in the through plant growth and and develop horticultural skills to ensure growth in
Metropolitan Region of Barcelona. Urban Studies 43: 1605–1623.
7 Syme GJ, Shao QX, Po M, Campbell E (2004) Predicting and understanding home garden water
release carbon in death. gardening in urban areas by individuals, schoolchildren and
use. Landscape and Urban Planning 68: 121–128. community groups.
6 www.rhs.org.uk/urbangreening www.rhs.org.uk/urbangreening 7
Ten tips for
domestic gardeners
While one person may only have a small
garden, when a street’s-worth is added
together, the amount of green space we
look after really adds up. In fact, our gardens
account for about 25 percent of the land
in most cities. And because more than
80 percent of the UK population lives in a
town or city, we can make a difference by
ensuring that every available space in our
front and back garden contains planting,
and that we carry out sustainable practices
1 Plant a tree to provide
shade and evapotran
spiration, to help cool
minimize annual soil
disturbance, helping
carbon capture.
the air in summer. Fast-
growing, deciduous
trees that require little
maintenance also provide
6 Consider reducing the
area of lawn in your
garden, replacing it with
maximum benefits in other permanent planting.
terms of carbon capture.
2 Plant a climber or hedge
to provide shade and
7 When renewing
garden equipment
bear in mind its energy
insulation for your house. and carbon efficiency.
3 Minimise/avoid paving
over large areas of
your garden, and consider
8 Make compost and
mulch, covering garden
soil with organic matter
replacing existing such as bark to prevent
impermeable paved areas evaporation of water.
with permeable surfaces,
including vegetation.
9 Collect rainwater and
use ‘grey water’
4 Plant a variety of plant
types and species to
support a range of wildlife,
(previously used for
washing dishes, baths etc
and suitable for small
eg a mix of trees, shrubs scale, short-term use).
and flowering plants.
5 Grow perennial plants
over large areas. As
10 Think ‘right plant,
right place’ to
minimise water use and
these grow in the same maximise energy saving
place year after year they and energy capture.
Prepared by Dr Tijana Blanusa (RHS)
and Abigail Page (independent
For more information please visit consultant), with thanks to
rhs advisory / leigh hunt
www.rhs.org.uk/urbangreening Dr Ross Cameron (University of Reading),
Dr Ken Thompson (University of Sheffield),
or email: gardeningadvice@rhs.org.uk Jane Taylor (University of Reading),
©2011 Royal Horticultural Society, 80 Vincent Square, London SW1P 2PE. Leigh Hunt (RHS), Dr Roger Williams (RHS),
0845 260 5000 RHS Reg Charity No. 222879 / SC038262 Chris Young (RHS)
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