Now, many green roofs are not garden roofs. They are not full of lush, tropical vegetation with nitrogen fertilizers added and irrigated with water that should be charging our aquifers. The latest argument for irrigation of green roofs - is - it is OK if the irrigation water comes from recycled stormwater. Sounds good, right! But how many of proponents of rainwater recycling actually have had rainwater systems in place for some time? If they do they will tell you that the cisterns are empty most of the time! Yes, we have an annual rainfall amount of well over 50 inches per year, but we also have extended periods of time where there is little if any rainfall.
So the proponents of irrigated green roofs say - use city water backup!
I thought we were in water conservation mode here. Watering restrictions, etc...
Just don't irrigate your vegetated roof. Use native species! The other day on a conference call an engineer referred to the native species of plants as 'Weeds!"
It is all perspective. I like the thought of using native species, not irrigating and still having a great vegetated roof.
The above photo is a test panel at UF that has been sitting in a back lot with less than an inch of soil average for almost a year with no irrigation or fertilizer and is still functioning to drink and clean stormwater and provide habitat for pollinators, etc...
No, it is not Jungle Gardens. But it is a thriving, functioning Green Roof! Remember - there is a difference between Intensive Green Roofs that are irrigated, weight 10 times as much or more and cost ten times as much or more - and require massive structural support - and Extensive Green Roofs that are light weight, non-irrigated, non-fertilized and can be put on simple structures.
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