The drive to green our urban spaces has lead to planting schemes in more unusual locations, such as vertical walls and green screening. With large foliage areas and small root systems, irrigation and the addition of nutrients is essential.
Vertical Green Walls
Vertical green walls have many of the benefits of green roof structures, but with the advantage that there are many more vertical spces that can be covered, and they are generally more visible, enhancing the environment for more people.
Green walls can be divided into two broad categories: 'natural' and 'artificial'. Natural green walls use plants that would naturally climb, such as Virginia creeper or climbers. Trellis or wires can be used to assist the plants to cover the walls. Irrigation is desirable but not essential. Generally a drip irrigation system at the root zone will speed up coverage of the wall and reduce growth problems during drought.
For artificial green walls, irrigation is essential, as is a method of supplying nutrients. Artificial systems generally have the root zones packed into frameworks hung onto the wall, with little chance of the plants obtaining a natural source of water. For these systems, such as the G-Sky wall pictured right, irrigation and nutrients must be supplied using drip pipes built into the structure.
Control systems need to take account of the changing weather conditions, as water requirements will vary enormously depending on aspect and weather.
It is vitally important that the irrigation system is an integral part of the design, not an afterthought.
Retaining Green Walls
Steeply sloping sites benefit from planting both visually and in terms of soil stabilisation. The steep slopes, however, create difficulties as moisture will very quickly drain down to the base of the slope. During establishment this can lead to high plant failure rates at the top of the slope, especially during dry weather. This, coupled with the practical difficulties of replanting fails specimens, makes irrigation a sensible option.
Generally the slope will be irrigated using drip line laid on or just below the surface. Spacing will depend on the planting type and the steepness of the slope. Check valves may need to be included to ensure that the water does not drain down to the lowest point.
Hanging Planting
Planters with trailing foliage are often used to soften hard landscape areas such as car parks or ugly post war buildings. Large planter boxes will support extensive trailing plants, sometimes with additional support wires. The foliage volume is very large compared to the root area, making regular irrigation and the supply of nutrients essential.
Generally the irrigation system will deliver the water using drip lines or individual drippers. Fertiliser can be drawn to the system on a pre-programmed basis - often a weekly cycle.
Main image: Green wall produced and installed by Kernock Park Plants for Sarah Eberle's RHS
Hampton Court 2008 show garden 'Holiday Inn Green Room'
