One of my interests is alpine gardening on small area. My dearest alpine garden is on the roof of my garage, with sedum, sempervivum, saxifraga, campanula cochleriifolia, etc. This has survived more than 15 years now, through some cold Dutch winters and hot dry summer periods, almost without any additional watering (the roof is in the North, mostly semi-shaded). Not much maintenance is required, but for one continuous plague: grass. If not pulled out regularly, grass will quickly overgrow the alpine plants. This is a bit unexpected because I never put on any fertiliser and the soil must have become rather poor in nitrogen in all these years. Any suggestions to mitigate this problem? Another problem was a leaking roof during heavy rain but that has been solved nicely.
I would like to contact others having the same type of roof garden, to exchange experience, also about the type of plants that do well under these conditions.
Louis Harmsen
