Green Roof: Plant Selection

Selection of plant material

The ideal characteristics of the plants to be selected are that they are drought resistant and wind resistant, they small low growing, easily reproduce themselves from seed in the event that the plants die of during times of extreme heat or drought. In addition it is of advantage if they have a creeping habit so that they are easily able to fill gaps left by die back during times of moisture stress. However plants with a vigorous creeping habit are unsuitable. The plants selected must easily root themselves for easy and cost effective planting. For instance plants such as Sedum are mostly used in Europe because cuttings of the desired species are made which are then able to be simply distributed over the surface to be planted either by hand or by mechanical means. In Europe various species of Sedum have these ideal growing characteristics which results in them being almost exclusively used in root greening projects. Here in South Africa we are fortunate to have a very similar growing closely related genus to Sedum being Crassula which has many of  the characteristics of the ideal green roof plant. In addition we are also blessed with a wide range of other light weight low growing succulents plants which are to a greater or lesser degree suitable for extensive roof greening. 

Water gardens are another innovative way of making a roof garden.

Fertilize at a rate of 100grams per square metre of 2:3:2 (22) + Zn at initial soil preparation then 30grams per square metre of 2:3:2 (22) + Zn every 3 months after planting. It has been found that fertilizer in March, June, September and December are the most useful months to do this fertilizing on the KZN Coast. Use 100grams/square metre of Dolomitic Lime once a year in spring. Fertiliser is to be applied to the soil during maintenance at the following rate.

For optimal plant growth in gardens with high sunlight areas, fertiliser and compost should be added twice a year, early spring around August and then in midsummer during December. It is essential that this process is then continued for, at least, the first 3 growing seasons after planting. The application rate is 30grams/m2 of 2:3:2(22) + Zn. 

Compost must be added every second year just to give the roots extra help on these shallow soil. In fact all leaf sweepings from the Ilanga Development should be spread around the roots on each garden in turn. This would be a first in South Africa!

FOR ZIMBALI

Flat roofs are best and it is up to the ZEMA Architectural Review Committee to decide where these flat roofs should be if at all. 

Ensure that there is a safe access onto the roof either fixed to the dwelling or as a removable ladder/steps that is designed to allow plants and materials to be easily and safely carried onto the roof. See the image attached for a simple and neat way of accessing each roof for installation and maintenance in the future.