Hedges and Their Environmental Benefits

Scientific research has shown the unique environmental benefits offered by certain hedging plants, shedding light on which varieties to grow and how to optimise their advantages.

Hedges serve as dynamic boundaries within our landscapes, offering not just visual appeal with their year-round foliage, but also serving as havens for wildlife and contributors to various ecosystem services. Despite the need for periodic maintenance, their multifaceted benefits make them a super alternative to traditional boundaries like fences and walls.

The understandings shared here stem from comprehensive research, which delves into the scientific evidence surrounding hedging plants’ contributions to ecosystem services. This pioneering study allows us to pinpoint the specific benefits offered by different hedge plants, although it’s conceivable they may provide even more benefits that await further scientific exploration.

The Eco Benefits of Planting Hedges

Reduce Air Pollution

The detrimental effects of poor air quality on human health, particularly respiratory and cardiovascular health, are well recognised. While the ability of plants to manage air pollution is widely acknowledged, precise quantification of the effectiveness remains unfounded. Nonetheless, hedges, acting as natural buffers between sources of pollution such as traffic, demonstrate a beneficial impact, notably in enhancing air quality within the immediate vicinity of these green barriers.

Flood Management

As towns and cities grapple with the escalating challenge of rainfall management, exacerbated by the diminishing presence of porous surfaces and the anticipated increase in heavy rainfall events linked to climate change, the urgency of the matter becomes apparent. A survey conducted by the RHS in 2016 revealed that a concerning proportion of UK front gardens are paved over, with a significant portion lacking any vegetation. Nevertheless, strategic planting can provide better resilience against flooding incidents across the UK.

Wildlife Habitat

Hedges play a pivotal role in urban ecosystems by fostering a rich diversity of animal species. They serve as vital havens for all kinds of creatures, offering shelter, nesting sites, food sources, and interconnected pathways for movement, thus facilitating the survival and thriving of various wildlife, even within urban environments.

Noise Reduction

Vegetation boundaries, such as hedgerows, hold the potential to mitigate noise levels by as much as 8 decibels. This is particularly significant given that extended exposure to noise levels exceeding 40 decibels during nighttime, and 65 decibels during daytime, is deemed detrimental to human health.

Other Benefits of Hedging

Hedges offer a plethora of additional environmental and practical advantages, although these have received comparatively less scientific study. Among these benefits are their capacity to provide shelter, regulate temperatures by offering cooling effects, and contribute to carbon offsetting. Hedges aid in the purification of soil pollutants. Furthermore, their visual appeal has been observed to reduce stress levels by providing visually stimulating surroundings.

Hedges and Their Environmental Benefits

How Can I Benefit From Planting a Hedge?

To begin, identify the benefit that holds the highest priority for you. For instance, if you live near a busy road, pollution and noise reduction may be of utmost concern. Conversely, if you have a fondness for wildlife, prioritising plants that support and attract it would be fitting. Subsequently, refer to the corresponding section below for optimal plant selections and design strategies.

It’s important to remember that the plants listed will offer additional benefits. Rarely does a plant excel solely in one aspect; instead, it typically provides multiple advantages. Therefore, if your aim is to maximise benefits across the board, consider planting:

• Beech (Fagus sylvatica)
• Holly (Ilex aquifolium)
• Red Japanese rose (Rosa rugosa)
• Privet (Ligustrum species and cultivars)
• Western red cedar (Thuja plicata)

Hedge Specific Benefits

Capturing Air Pollution

The way these hedges reduce pollution involves plants with small ovate, rough, hairy, or scaly leaves effectively trapping tiny dust-like particles, known as airborne particulate pollution. These particles are then either washed to the ground by rain or shed along with old leaves.

To maximise the benefits of pollution reduction, cultivate large and dense hedges to optimise the surface area available for trapping pollutants. Aim for a height of at least 1.5 meters (5 feet) and a depth of 1 meter (3⅓ feet). Choose from the plant list below. Theoretically, a single plant grown to these dimensions has the potential to capture pollution equivalent to that emitted by 60 diesel cars annually. While real-world results may vary, this highlights the significant pollution-capturing potential of plants and hedges.

• Cotoneasters
• Elaeagnus × submacrophylla (syn. Elaeagnus × ebbingei)
• Common yew (Taxus baccata)
• Western red cedar (Thuja plicata)

Reducing Carbon

Plants absorb carbon dioxide from the air through pores, utilising some of it to build their woody structure. Faster-growing plants have the ability to store more carbon within a shorter timeframe. While large, mature hedges have the highest capacity for carbon storage, the overall amount stored reaches a plateau once they are maintained at their desired size.

To maximise carbon reduction benefits, select plants from the list provided below and allow the hedge to reach maturity. Enhance carbon sequestration by composting the clippings and incorporating the resulting compost into your garden. Additionally, utilise mulch in your garden, as soil serves as an excellent carbon storage medium.

• Beech (Fagus sylvatica)
• Bay (Laurus nobilis)
• Laurustinus (Viburnum tinus)
• Western red cedar (Thuja plicata)

Cooling Your Garden with Hedges

Hedges facilitate cooling by shading the surrounding area and releasing cooling water vapour through transpiration. Moreover, they offer insulation by acting as a barrier against the wind, thereby reducing the “wind chill” effect on adjacent buildings.

To optimise these cooling and insulation benefits, select plants from the list provided below. Larger hedges possess a greater surface area, enabling them to shade and transpire more effectively, although hedges of any size will offer proportional benefits. Planting on the sunny side of your garden ensures that the hedge casts more shadow during the summer months. Additionally, if you reside in a cold region, opting for deciduous plants allows sunlight and warmth to penetrate through during the winter.

• Cherry laurel (Prunus laurocerasus)
• Cotoneaster franchetii
• Forsythia × intermedia
• Lonicera ligustrina var. yunnanensis (syn. Lonicera nitida) and cultivars

Hedges and Their Environmental Benefits

 

Flood Risk Reduction

Plants with expansive leaf surfaces, elevated rates of transpiration (i.e., releasing more water vapour from leaves and stems), and evergreen canopies are linked to increased retention of rainfall. They slow the descent of water to the ground and diminish water runoff by enhancing the soil’s capacity to retain moisture.

To maximise these benefits, cultivate a larger hedge, as it will possess a greater surface area, thereby improving its effectiveness. Select plants from the list provided below, with particular emphasis on evergreens, as they contribute significantly to rainfall retention.

• Cotoneasters
• Forsythia × intermedia
• Hawthorn (Crataegus monogyna)
• Privet (Ligustrum species)

Noise Reduction

The leaves and stems of plants serve as a physical barrier to noise transmission.

To maximise the noise reduction benefits, select plants from the list provided below. Aim to cultivate a hedge that is both wide and tall, ideally reaching at least 2 meters (6⅔ feet) in height. Evergreens with dense canopies are particularly effective, reducing noise levels by approximately 8 decibels. Regular clipping of the hedge over a period of 5-15 years will enhance the density of the surface, thereby increasing its effectiveness as a noise barrier.

If noise reduction is a primary concern in your garden, consider complementing the hedge with a barrier such as a panel fence or brick wall.

• Cherry Laurel (Prunus laurocerasus)
• Common yew (Taxus baccata)
• Holly (Ilex aquifolium)
• Japanese barberry (Berberis thunbergii)
• Western red cedar (Thuja plicata) – evergreen

Wildlife Friendly Hedges

Hedges primarily provide shelter for birds, with certain varieties like common yew, hawthorn, and pyracantha offering additional benefits by providing food such as berries and flowers that attract insects for pollen and nectar.

To optimise the benefits for wildlife, consider planting a mix of hedges that extend flowering and fruiting times. This can consist of a combination of the plants listed below or a native mixed hedge, which typically includes plants like beech, hawthorn, and roses. However, supporting wildlife goes beyond just planting a hedge, so remember to incorporate other insect and bird-friendly plants into your garden as well.

• Beech (Fagus sylvatica)
• Common yew (Taxus baccata)
• Hawthorn (Crataegus monogyna)
• Red Japanese rose (Rosa rugosa)
• Privet (Ligustrum species)
• Pyracantha (firethorn) cultivars

Hedges and Their Environmental Benefits – How Much Difference Does it Really Make?

While hedges offer advantages within individual gardens, their impact on a larger scale, such as an entire street, hinges more on the overall quantity of greenery compared to built surfaces.

In a small garden, focusing on cultivating large, dense hedges that absorb and release ample water can effectively reduce temperatures, making plant selection crucial in such confined spaces.

However, at the scale of a whole street, temperature regulation is influenced by various factors including building characteristics, weather conditions, and air circulation. Here, the ratio of green to built surfaces becomes paramount, outweighing the significance of individual plant choices. Maximising green spaces over grey surfaces yields the most substantial benefits.

One notable exception, to a certain extent, is the role of gardens in supporting wildlife. Gardens serve as vital corridors and stepping stones for wildlife regardless of their size, underscoring the continued significance of thoughtful planting choices.

How to plant hedges

Evergreen and semi-evergreen hedges are best planted in late October, early November and March. Deciduous hedges can be planted from late October until March, as long as the ground is not frozen at the time of planting.

How Much Maintenance Do Hedges Need?

Hedges typically require maintenance to prevent the plants from growing into trees and to promote a dense face and top. This usually involves trimming once or twice a year. The frequency of cuts depends on the specific hedge species and its growth rate.

– Bay (Laurus nobilis): Evergreen. Hedge heights of 1.2-2m (4-6⅔ft). Average number of cuts per year: one.
– Beech (Fagus sylvatica): Deciduous. Hedge heights of 1.2-6m (4-20ft). Average number of cuts per year: one.
– Common yew (Taxus baccata): Evergreen. Hedge heights of 1.2-6m (4-20ft). Average number of cuts per year: one.
– Cotoneaster franchetii (cotoneaster): Semi-evergreen. Hedge heights of 1.5-2.4m (5-8ft). Average number of cuts per year: two.
– Cherry laurel (Prunus laurocerasus): Evergreen. Hedge heights of 2-4m (6⅔-13ft). Average number of cuts per year: one to two.
– Elaeagnus × submacrophylla* (syn. Elaeagnus × ebbingei): Evergreen. Hedge heights of 2-3m (6⅔-10ft). Averagenumber of cuts per year: two.
– Forsythia × intermedia: Deciduous. Hedge heights of 1.2-2m (4-6⅔ft). Average number of cuts per year: one, after flowering.
– Hawthorn (Crataegus monogyna): Deciduous. Hedge heights of 1.5-3m (5-10ft). Average number of cuts per year: two.
– Holly (Ilex aquifolium): Evergreen. Hedge heights of 2-4m (6⅔-10ft). Average number of cuts per year: one.
– Japanese barberry (Berberis thunbergii): Deciduous. Hedge heights of 60cm-1.2m (2-4ft). Average number of cuts per year: one to two.
– Laurustinus (Viburnum tinus): Evergreen. Hedge heights of 1.2-2m (4-6⅔ft). Typical number of cuts per year: one, after flowering.
– Lonicera ligustrina var. yunnanensis (syn. Lonicera nitida) and cultivars: Evergreen. Hedge heights of 60cm-1.5m (2-5ft). Average number of cuts per year: two.
– Privet (Ligustrum species): Semi-evergreen. Hedge heights of 1.5-3m (5-10ft). Average number of cuts per year: two.
– Pyracantha (firethorn): Evergreen. Hedge heights of 2-3m (6⅔-10ft). Average number of cuts per year: two to three.
– Red Japanese rose (Rosa rugosa): Deciduous. Hedge heights of 1.2-1.5m (4-5ft). Average number of cuts per year: one.
– Western red cedar (Thuja plicata): Evergreen. Hedge heights of 1.5-3m (5-10ft). Average number of cuts per year: one to two.

Regular trimming ensures that hedges maintain their environmental benefits for many years. It’s common to see hedges outlast neighbouring fences, making them a cost-effective long-term option.

 Hedges and Their Environmental Benefits
The Science Behind it

For the Royal Horticultural Society (RHS) Science review, a selection of plant species commonly utilised in urban hedges across north-west Europe was meticulously curated. The methodology involved scrutinising nursery catalogues specialised in hedging, consulting with nursery businesses to identify the most popular plants sold, and analysing data from the RHS Gardening Advice service.

The chosen species encompassed the ‘top 25’ most frequently enquired about hedges received through the RHS Gardening Advice service, which annually fields over 110,000 enquiries from RHS Members and visitors to RHS Flower Shows. Additionally, 18 other species widely observed in urban areas across European temperate climates were incorporated based on anecdotal evidence. While many of these species are also prevalent in temperate regions of North America, Asia, and Australasia, the list excluded species primarily utilised in rural settings, such as within hedgerows or as windbreaks (e.g., Populus spp.). The focus remained on those tailored to address urban-specific challenges.