While young metro-agrarian trend setters around the country dive elbow deep into compost, one financial giant wants to get its hands dirty too. This multinational investment banking and securities firm (that prefers to remain anonymous), is constructing a raised bed production area on the roof of the firm’s newly acquired hotel in Lower Manhattan. The hotel is located in the affluent Battery Park City neighborhood, and will contain a restaurant that aims to incorporate rooftop produce into its menu.
The sophisticated rooftop design incorporates swaths of extensive green roof, decorative crushed glass, and rubber pavers in addition to the farm plots. Ken Smith Landscape Architect designed this layout, and hired Roofmeadow (the green roof firm for which I work) as the project’s green roof consultant. Roofmeadow maintains a national network of licensed green roof contractors, one of whom, the Sponzilli Landscape Group, is currently installing this project. I had the good fortune of visiting the site this morning to perform construction oversight, and was able to see the farm plots first hand.
The raised beds themselves are much like those on the ground plain, except that these beds more intricately address the threshold between soil and underlying substrate. Rooftop raised beds require a well-planned drainage system in order to maintain proper soil moisture in each plot. A bed that does not drain effectively can become waterlogged and kill the plants growing within. A bed that drains too quickly will require significant levels of irrigation, and will therefore produce weak plants while wasting water. The Embassy Suits Hotel raised beds utilize specially engineered growing media that holds a specific amount of water between its particles. This media sits on top of a sheet drain, which was selected for its specific transmissivity (or horizontal flow) rate.
Installing raised beds on a roof is much more expensive than on the ground, due mostly to costs associated with rooftop access and labor. This means that the beds themselves should ideally last much longer on a roof than on the ground, so that they do not need to be replaced very often. What material should be deployed, then? Untreated wood typically lasts 3-4 years when used for raised beds in the northeastern climate. Treated wood lasts longer, but proves toxic when containing edible crops. Cinder blocks and brick are sturdy options, except that they can easily exceed rooftop weight limits.
Ken Smith Landscape Architect chose cedar for the raised beds at the Embassy Suits Hotel. This wood naturally resists decay, and therefore acts as an ideal candidate for long-lasting rooftop raised beds. The downside? The specific wood used for this project may not have been sustainably harvested, and it was also extremely expensive. This is a wood that may be prohibitively expensive for most professional projects, and certainly would exceed the budgets of most at-home installations.
So what is the best material to use for rooftop raised beds? That’s up for debate. What do you think?