rooftop growing
The simplest roof gardens feature pots and containers . Balconies and other small spaces allow for garden towers or bees and chickens . Sloped roofs are still an option for living turf , though this super low-tech method is best suited to small outbuildings as it ’ s possible some modern homes couldn ’ t support the weight of thick turf . Alternatively , there are also living roofs , which are extensive areas of growing media less than six inches deep and planted with sedums , succulents , and hardy native plants . Such a living roof will add less than 50 pounds per square foot to the roof ’ s weight . A crop roof , on the other hand , is an intensive production zone with deeper growth medium , and it will add 80 to 120 pounds per square foot . If you have difficulty getting the media deep enough for crops directly on the roof , planting boxes can easily be constructed . Some tropical hardwoods and oily woods , like redwood and cedar , contain aromatic oils that resist rot . Longer lasting boxes can be built with synthetic materials or with a wood frame and corrugated metal liners . Whatever you decide , though , nix toxic treated lumber around food plants . One low-tech , low-cost growing space for shallow-root plants is manufactured roof troughs ( aka gutters ). Buy 10-foot lengths with end caps , long support nails , and hollow ferules that keep those nails in place for mounting . Inexpensive , larger-diameter pipes with drilled holes for plants are used in many higher-tech growing operations . ( Note that toxic chemicals leach out of PVC pipe , so don ’ t use that .)
Pros and Cons
No matter which type of rooftop growing you ’ re talking about , they all serve a variety of functions , including :
• A planted roof provides forage for small wildlife , birds , and insects . Native plants feed native insects and birds . Large areas of plantings contribute to fresher air and CO 2 absorption . Plus , a roof is up out of reach from animals and troublemakers .
• A living roof lasts many decades when done right . The sun ’ s high-energy ultraviolet ( UV ) rays break molecular bonds and destroy building materials fast . Living roofs prevent UV from reaching the waterproof layer . Plus , not having to rip off , dispose of , and replace a roof every 15 or 20 years saves an immense amount of money , energy , and materials over the life of the structure .
• Soil or planting mix dampens sound and provides good insulation . Plants give shade and , when they transpire , cool by evaporation . This reduces the urban heat island effect that contributes to making town centers hotter than surrounding areas . Thus , a living roof helps limit the advance of climate change and plays an integral role in sustainable design .
• It ’ s sunny up high where there is less shade . Most crops , from asparagus to zucchini , demand hours of daily sunlight to mature . In a city , the top of a building may be the one available place that ’ s not shaded by tall structures for much of the day . In a forested area , a roof might be the largest sunny spot around .
• Heavy flows of storm run-off , excluded from sewage treatment , pick up urban pollutants when water rushes over hard , contaminated surfaces to flood streets before it drains to streams . A living roof allows stormwater to be absorbed where soil organisms can break down toxins and the outflow drains away gradually .
• In big cities , where space is at a premium , rooftop gardens are coveted getaway spots , attractive to potential renters as a social spot or spirit-building retreat .
Now for the downside :
• Winds are fiercer up high and can rip away your work . The sun may be so intense you need shading .
• It ’ s tough to carry everything up there and haul produce back down .
• As with any garden , somebody must pay for water , seeds and starts , amendments , support structures , etc . and it requires commitment to regular care and maintenance .
• You will have failures .
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Despite some manageable drawbacks , any nearly flat roof can be gardened .”
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