Anyhow, back the greening of roofs. The most popular green roof option these days is the extensive green roof. That is one with waterproof barrier, topped by a shallow growing medium profile, and capped with planted plugs of low water use plants. The plants fill in after about a year or so, and succulents are a very popular variety because of their suitability for the conditions on top of roofs: increased wind, little shade, etc. But, rooftop gardening still captures the imagination (and stomachs) of many city dwellers. If you think about how global populations have been shifting away from rural areas into more concentrated urban environments, it makes sense that a desire to grow some food in cities might travel with that migration. But where do you find the space available? How about flat roofs? Of course, there are challenges: not only the climatic ones mentioned earlier, but access, structural integrity, and water sources are also big questions. How do you get on the roof? How much weight can it hold? Is there a water faucet or will you be hauling up buckets?
The Rooftop Garden Project in Canada has come up with some innovative, low-cost solutions to rooftop gardening. Most of their plantings are hydroponic for the main reason that it combines low weight with high moisture and nutrient delivery, perfect for lettuce and vegetables. Two of my favorites involve pipes and tin cans: