|[Eagle Street Rooftop Farm, Brooklyn, NY]|
|[Typical green roof section]|
Soil-based roof gardens are classified as either extensive or intensive. Extensive gardens have very shallow soil profiles (2" or less) and can only support small, shallow-rooting plants like succulents. Extensive roof gardens mitigate urban heat effects and slow and store stormwater runoffs, but cannot support larger vegetation. Intensive gardens have deeper soil profiles, sometimes to several feet depending on the structural capabilities of the building and the plant material desired. Intensive gardens can support edible plants, shrubs and even trees depending on how they are designed. Sometimes these two are differentiated as greenroofs (extensive) and roof gardens (extensive). Planted roof systems typically consist of a number of layers designed to protect the roof itself from water intrusion, and vary most in the design of the growing medium, which must be both lightweight and able to hold water effectively. Rapid water loss to evaporation is one of the major challenges to roof garden plants. Other options for roof-gardens include planter boxes, hydroponic systems, and greenhouses.
|[Gary Comer Youth Center edible roof garden, Chicago, IL]|
Gary Comer Youth Center roof garden in Chicago, IL is a non-profit in-place garden, growing 1,000 pounds of food annually and feeding 175 children at the center daily. Soil is 18-24" deep in growing areas. The garden won the ASLA Honor Award for General Design in 2010. The garden design translates traditional farm rows into a playful urban space by alternating the row sizes, and uses concrete bands between rows.
|[Uncommon Ground (top) and Ledge Kitchen garden (bottom)]|
|[Bell Book & Candle aeroponic garden]|
Hydroponics as a growing system has been shown to produce higher yields, and to use less water, than conventional growing methods. Hydroponics also make production available in places where there is no soil.
Bell Book & Candle is a New York City restaurant with a rooftop kitchen garden growing in aeroponic towers. A mist of nutrient-rich water nurtures a whole range of crops from greens to tomatoes. Sixty percent of the restaurant's produce is grown on the roof. The aeroponic system used by BB&C is a home system, readily available on-line.
Local Garden in Vancouver is a commercial hydroponic-based farm on a parking garage roof - read more in Grow City's earlier post.
How do these different systems compare for yields, management, and start-up costs? Any graduate students out there looking for a thesis topic? Knowing how the system will effect the success of the farm, and meet it's goals, is a crucial element in designing an edible rooftop. More on greenhouse rooftop gardens, and growing systems in a future post.