Green roofs are not maintenance free, and while intensive green roofs require as much care as any landscape on the ground, extensive roofs also need periodic tending. The amount of care depends on the roof’s exposure, the types of plants, the growing medium and the vagaries of the weather. The good news is, performing these periodic tasks can be a great excuse for inviting your friends and neighbors to check out your roof, and get better acquainted with green roofing and sustainable design.
Most green roofs will require some irrigation for up to 90 days to get established. Those that are modular, or already established before placing on the roof, will need regular moisture checks for a few weeks. This is especially important when the weather is hot and dry since the plants may not be acclimated to the higher stresses associated with roof living.
Extensive roofs can benefit from drip irrigation systems that can be turned on during periods of extreme drought when the plants are under stress. Otherwise, making sure there is a hose bib available so you can water the plants with a hose is a good idea. Generally though, if the right plants were used then whenever the weather is typical for your region you should not need to water them once they are established.
Intensive green roofs on the other hand use plants with higher water needs then extensive roofs, so they will require some form of irrigation. Winds are often more intense higher up where there is not as much to block them so the drying effect will be greater and will wick moisture away from the plants more quickly. This is where it is important to include an irrigation system at the time the roof is installed.
While fertilizing green roofs is not always listed in the best practices for maintaining the plants there is evidence that fertilization with the right type of fertilizer in the right type of planting medium has beneficial effects. In one study (PDF) conducted on the roof of the engineering building at the Edwardsville campus of the Southern Illinois University, one type of fertilizer being used on a particular type of Sedum in a pumice growing medium showed better plant growth and overall health than a control group that was not fertilized, and another group that was fertilized with a different fertilizer. The University of Florida Extension suggests fertilizing with a slow-release fertilizer twice each year.
Sellers of green roof systems include checklists of maintenance activities that include inspecting for damage, roots penetrating the membrane, blown-in debris, weed growth, dead and dying plants, disease and pests, fertilizing needs and uncontrolled over-growth. GreenRoofs.com suggests inspections for invasive weeds, plant diseases and pests and stray tree seedlings at least twice a year. Some plants may have to be replaced especially during the establishment phase.
Companies that install green roofs also point to the necessity to keep gutters and drains clean and in good repair. These items periodically need to be re-caulked, repaired or replaced. Manufacturers or installers may offer maintenance plans for the establishment period or may include them in the installation price.
Most maintenance tasks for extensive green roofs are within the abilities of the roof owners so it’s just a matter of deciding if you want to have a few chores on the roof every now and then, or you’d rather sit back and watch someone else do them. Intensive green roofs can have maintenance requirements equal to a ground-based landscape and are often best left to the professionals.
Finally, I wanted to recommend one last resource that will help you keep tabs on how the pros do annual checks of green roofs in bigger buildings. These reports from green design group Projects in Place contain invaluable, detailed notes and photographs of periodic maintenance issues that can come up, and document the steps taken to resolve them.