Hello, I'm actually an Architecture student currently working on a project and wondering about possibilities over planting trees on the rooftop. I am currently trying to propose a garden with cherry trees (probably Canada Red Choke Cherry) over a concrete roof and wondering if it is a bad idea. I researched around however I wasn't sure about how deep the tree roots would go and couldn't find any information on planting over concrete dealing with cherry trees in particular. If it is possible without creating damage in the long run to both the building and tree, I was wondering how deep of soil I would have to produce and maybe ideas on what kind of treatment beneath the soil near the concrete should be like (drainage mat maybe?). If it is not possible, what kind of plants/trees would be nice for landscaping on the rooftop? (Restaurants have direct access/view to the roof top) I'm by all means not very knowledgeable in this subject area so I thought to seek some help after having read some interesting posts. Any help would be greatly appreciated. Thank you.
I am no expert here, but most trees have extensive root systems. The spread below the soil is often comparable to the spread above. I think the weight of that much soil would be a an issue. Fruiting shrubs and vines would probably be more practical. There are a lot of variables here on both the construction and horticultural sides. You have to consider the weight, potential leaks, roots growing into the support of the roof and things like irrigation, air quality (many plants will not thrive in urban settings) and pollination for the growth of the plants. There is a lot of research on the topic. A search for "green roofs" returns many pages. http://www.greenroofs.org/ http://www.toronto.ca/greenroofs/index.htm http://commons.bcit.ca/greenroof/
You might also want to look at how green roofs can be a problem to insurance companies. I know that some people have had problems in Vancouver but, having said that, our local RCMP station roof is green and so are the roofs in a new development of ecco. friendly homes which have just been completed here. This may or may not have any impact on your assignment. Margaret
I have read a few articles on green rooftops in the past, and I found them quite interesting. I hope to enter into the architecture program at Dalhousie here in Halifax after pre-reqs, and green designs have drawn my attention. Of course I'm no expert on what can be done, but the biggest issue seems to be weight. I believe a cubic ft. of soil can weigh nearly 100 lbs., depending on the moisture content and components of course. I'm not at all knowledgable about cherry trees, but might there be a possibility of using a cherry grafted onto a dwarf rootstock? I'm not sure if such a thing exists, or if could produce fruit in 3-4 cu.ft. of containerized soil, but I supose it's worth researching. Most green rooftops seem to use hardy grasses/shrubs in a thin, well-drained layer of soil anchored to a drainage mat.
