Extensive green roof being planted - Kat Harrold
By Kat Harrold GRP
A common misconception with green roofs, especially extensive ones, is that they require no maintenance. While some green roofs may be fairly self-sustaining and require little maintenance there is still some regular maintenance required to keep the green roof as a system working to it’s fullest. The three main things to consider are the plants, media, and timing.
Plant selection is very important in determining when you need to fertilize and weed. Also deciding what is a weed is very important. A weed very often is as subjective as beauty; often it is simply within the eye of the beholder. Newly planted green roofs will need more weeding than established roofs to cut down on competition of resources while they try to get a foot-hold.
Green roof media blended properly should have very little organic matter. While extensive green roofs generally don’t require much additional nutrients they do need a balanced low-level fertilizer with micro-nutrients applied twice a year. Do NOT use an organic fertilizer such as manor or compost. The organic material can break up into very fine particles, which over time could clog the filter fabric and cause drainage problems. Specifics on fertilizer content for green roofs can be found in the translated German green roof guide the FLL.
Timing is very important in terms of preserving both plants and your sanity. On an establishing extensive green roof be sure to weed once every 2 months for the first year. You can cut back your weeding to 3-4 times a year once the plants have established. Taking extra care in the springtime and after a heavy rain can save a lot of time weeding seedlings instead of full grown weeds. Grasses should be cut back in late winter to early spring. FLL specified fertilizer should be applied once in the spring and once in the fall for the first year. Have a professional check your roof after that to advise how much is needed there after.