The Chelsea Flower Show is in full bloom. The UK’s annual botanical extravaganza celebrates all aspects of horticulture and is an important venue for watching emerging trends in the gardening world. But how can we maximise the green spaces we have to hand and also benefit the environment?
In the UK, domestic gardens represent 20-25% of a city’s area and the vast majority of urban residents have access to one. What we grow in these green spaces and –- importantly – how they are managed, could have a significant environmental impact within our cities.
There are a number of ways that plants and gardens provide positive and negative “services”. For example, scientists are confident that plants provide localised cooling, decrease the risk of flooding and support biodiversity. They are also confident about the risks and the extent of potential damage from using peat, chemicals and fertilisers in plant management. It is therefore critical that we use this knowledge to maximise the positive impact of our green spaces.
Much as different management practices have a smaller or greater environmental impact, plants themselves can differ a huge amount in the different benefits (and costs) that they entail and provide.
In a recent study focusing on the cooling service provided by green roofs, our Royal Horticultural Society science team found that broad-leaved plants cooled their own and surrounding surfaces better than the traditionally used succulent plants. This is because the broad and thin-leaved plants use and lose more water than thicker-leaved succulents, cooling better through the process of transpiration. In our outdoor experiments, on a hot sunny summer day this led to broad-leaved Stachys byzantina (Lamb’s Ear) cooling the soil (and so potentially a roof surface if planted there) by a huge 12°C more than a covering of succulent Sedum.
Plants can capture and temporarily hold pollution particles from the air (such as from fuel burning and vehicular emissions); they can also take up gaseous pollutants like nitrogen dioxide and sulphur dioxide. Research suggests that plants with complex leaf structures (including rough, hairy leaves) are likely to be capturing more pollutants across the range of particle sizes.
Conifers such as Leylands and pines have been shown to accumulate more particles (in the size ranges greater than 2.5μm) on their surfaces than broad-leaved tree species such as poplars, maples or whitebeams. But both broad-leaved and conifer species have been shown to accumulate well the finest particles (less than 1μm), potentially most detrimental to human health.
So, growing longer-life, perennial plants such as trees and shrubs in our gardens will help decrease our carbon impact, enabling longer-term carbon storage in the plants and the soil.
Four ways to ‘green up’ your garden
There are some simple and effective steps you can take in your own garden to maximise the positive environmental contribution of your green spaces, decrease the risk of surface flooding, insulate your house using vegetation and support biodiversity.
Plant climbers and wall shrubs Most of us have walls and fences that have space for a climber or wall shrub. Using these leafy coverings helps insulate homes in winter (reducing heating bills) and keeps them cooler in summer. You can even go up the wall with plants by installing green-wall planting systems.
Grow plants for wildlife
When it comes to encouraging wildlife, it’s a case of the more plants the better. Aim to grow as many different types of plant as you can, including natives, and provide as much cover as possible. This should help ensure that you provide food and shelter at most times of year.
Use permeable paving
Think carefully before you pave over your front garden. Where paving is necessary, keep the area as small as possible and use permeable materials (planning permission is required for non-permeable materials). These measures allow the rainwater to soak into the soil, rather than causing flooding.
Install green roofs
Any birds-eye view of a town or city reveals that roofs cover a substantial area. It is possible to turn these barren spaces into planted surfaces by installing a green roof. These range from plant mats rolled out over a prepared base to flowery coverings grown in deeper soil – just make sure your roof can take the weight. Worth considering on your new shed or an extension, green roofs help reduce flooding and cool the surrounding surfaces and air.