Several factors influence the quality and the lifespan of a green roof. For instance, if certain components are wrongly selected, dominating plants may start overgrowing the green roof.
Climate conditions can be important, too. Sedum requires at least three hours of sunlight during the Summer. When periods of drought last for more than 5-6 weeks, irrigation is needed.
Other species thrive better in shadowy areas or can withstand longer periods of drought.
Design and maintenance require attention, as well. Do bear in mind the following:
choose the right substrate. A wrong choice of substrate, or the wrong composition, increases the likelihood of undesired vegetation developing. The share of organic matter must be adapted to the vegetation;
determine the water-retention capacity needed for the vegetation. Too high a water-retention may prove disastrous as undesired vegetation would develop lavishly;
execution of roof details. You would want to minimise the risk of (unwanted) vegetation damaging roof details.
As soon as the vegetation has been put on the roof, you need to fertilise it using an organic fertiliser, and you need to irrigate it adequately.
Whatever the type, all green roofs require maintenance.
Extensive green roofs: low maintenance
Contrary to other types of green roofs, extensive green roofs require only little maintenance. However, that does not mean that no maintenance is required at all. During the first year, we recommend to control extensive greening each quarter. From the second year onwards, one yearly inspection should suffice. In the first two years, maintenance can take place in Spring and in Autumn. Afterwards, one maintenance session per year, in Spring, should be enough.
remove parasitic plants with roots and all;
replace dead plants and sow bare spots;
check on erosion in the substrate (on sloping roofs);
remove waste, such as dead leaves which have piled up;
in case vegetation mats would have shifted: put them back in place;
check all roof details.
Intensive green roofs: same level of maintenance as an ordinary garden