Vertical gardening

Why growing up is in

In 2008, at the premium horticultural event of the year, the Chelsea Flower Show, vertical planting was presented in a number of show gardens. Inspired by plants in rainforest canopies or living on rocks around waterfalls the key features were green roofs and planted walls.

The wealth of benefits from this planting style includes reducing pollution and rainwater run-off, insulating buildings and providing habitat for wildlife. Vertical gardening can offset the impact of paving over front gardens, increasing vegetation in otherwise concrete-filled spaces and reducing the risk of localised flooding.

Research by the Centre for Sustainable Development at the University of Cambridge has found that "a layer of vegetation can reduce heat loss from buildings, cutting the wind chill factor by 75% and heating demand by 25%."

However, advantages go beyond the eco-friendly. Obviously there's the visual impact and pleasure of beautifying buildings but it can also provide screening, reduce noise and even have a positive impact on peoples' health.

Origins and the future

The world's largest green wall, known as the Bio-Lung, was unveiled at Expo 2005 in Japan. At 150 metres long, 15 metres high and containing 200,000 plants of 200 different species, it was a representation of how plants can act as lungs for a city.

In the UK, green roofs are gaining popularity and going mainstream according to Dave Austen of Greenfix Sky Gardens, UK green roof specialists. In some German cities green roofs are now a legal requirement for flat-roofed buildings with coverage rising by over 13 million square metres a year. Dave explains that UK planning regulations are now leaning in the same direction, with "new buildings required to have a proportion of green walls and roofs".

Even nightclubs and shopping centres may soon be covered in foliage as club owner Billy Reilly opens a new five-storey venue called The Driver in the heart of King's Cross with a living system on its façade, created with the help of famous French vertical gardener Patrick Blanc. And Westfield, a shopping complex in west London that opened in October 2008, boasts an impressive vertical garden that's lit up at night.

An inspirational project is being masterminded in the same area of London by the King's Cross Community Projects, where an ugly wall on Wharfdale Road has been described by project co-ordinator Sophie Talbot as "the bane of our lives". "Anything we can do to lessen the carbon dioxide and gunk thrown out by diesel engines is a good idea. We hope to create interest throughout the year with seasonal, successional planting, subtle lighting and ideally use indigenous plants".

How does it work?

Plants need soil for support and to provide water and nutrients essential for growth. If you provide an alternative source of these many plants can actually grow without soil. This is known as hydroponics and the water and nutrients are supplied through irrigation systems.

The traditional method of growing vertically is to simply train a plant such as ivy or clematis up a wall. New ideas take this further; integrating plants into walls and roofs, and adding structures, containers and supports to buildings to be used for planting.

This new style of gardening changes the way we think about roof gardens too. Roof terraces are usually confined to containers and if you wanted to lay normal soil you needed a roof capable of supporting it. Now there are new lightweight growing media available, such as LECA (light expanded clay aggregate).

New approaches to green roofs mean areas are not always designed as gardens or roof terraces to use and enjoy and may be an area of grass or drought-tolerant planting, inaccessible and simply overlooked instead.

Wall technology

Stopping roots penetrating deep into walls is easier than you might think. The solution is to provide a water supply so the plants' roots don't need to keep growing in search of water. Designer Patrick Blanc conceived a way of supporting plants in a lightweight metal structure lined with PVC and rot-proof felt and added an automatic watering system complete with fertiliser.

Ready-planted wall panels are available in the UK and can simply be mounted and the irrigation plugged in. Green walls can even be installed indoors and fed from a reservoir which trickles water down the grid of plants.

Up on the roof

Flat roofs are the best for greening and a flat, asphalt-covered garage is ideal for a carpet of sedums. By adding a concrete support filled with growing media you could choose to grow a wildflower meadow.

Tiled or corrugated garage roofs are not suited to living roofs but will support moss and lichen which are useful wildlife habitat. You can develop a green roof on your shed but many need additional reinforcement first.

Follow our step-by-step guide to building a green roof here.

Keeping up tradition

If you want some of the benefits of vertical gardening with less construction work there are more traditional methods of smothering a wall in blooms. A simple wire framework or trellis can be used to train a climber against your house, garden wall or fence. For all year interest use an evergreen favourite such as ivy and intersperse with flowering climbers such as jasmine, honeysuckle or clematis. Alternatively create interest at eye level by mounting planters on your wall to fill with trailing flowers.

Seeding sedums

You can establish a sedum blanket from seed and obviously this is the cheapest option but will take time to establish. Cuttings are another option or for instant impact use a pre-sown sedum blanket which can have wildflowers added as an option.

Ideally include native sedums such as biting stonecrop, Sedum acre, which grows into a mat of twisting stems with tiny, green leaves.

Five sedums to try

• Sedum acre
• Sedum album
• Sedum hispanicum
• Sedum reflexum
• Sedum spurium 'Dragons blood'

Plants to try

Choosing the right plants needs thought as conditions for growth are not ideal; plants may need to withstand drought, extreme temperatures, high light intensities and strong wind. Look for plants adapted to cope with these harsh conditions.

The plants available to you depend on the depth of soil you create:

• 0–5 cm - Sedums, mosses and lichens.
• 5–10 cm - Short wildflower meadows, low-growing, drought-tolerant perennials, grasses, alpines and small bulbs.
• 10–20 cm - Mixtures of low or medium perennials, grasses, bulbs and annuals from dry habitats, wildflower meadows and hardy sub-shrubs.

With careful planning your green wall or roof will need minimal maintenance, just sporadic weeding to remove woody plants that have invaded. If you concentrate on developing a moss and lichen community remember to be patient, some lichens grow less than a millimetre a year. If you can’t wait, invest in pre-grown moss mats.

Five to try at 5-10cm soil depth

• Lotus corniculatus - Bird's foot trefoil
• Primula veris - Cowslip
• Hieracium lanatum - Leafy hawkweed
• Anthyllis vulneraria - Kidney vetch
• Trifolium pratense - Clover

Five to try at 10-15cm soil depth

• Knautia macedonica- Field scabious
• Centaurea scabiosa - Greater knapweed
• Origanum vulgare - Wild marjoram
• Echium vulgare - Viper's bugloss
• Linaria vulgaris - Toadflax