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Rooftop Gardening

Rooftop Gardening

July 1, 2009

Interest in rooftop gardening is skyrocketing, or should that be skyscraping.
Urbanites longing for an outdoor space to dig in the dirt have chosen to go up.
Beauty and the vibrancy of life are topping buildings, but rooftop gardens do
much more. The urban ecosystem (and everyone in it) benefits from the positive
environmental properties of growing plants. This is not just gardening, but greening
because it improves the landscape for the benefit of humans and the environment.

Rooftop gardening (including green roofs): reduces storm water runoff, combats the
heat island effect, acts as a bio-filter, and provides wildlife habitat. In addition,
rooftop gardening can save money by prolonging the life of the roof, and perhaps
qualifying for a tax subsidy. (Both Chicago and New York offer tax incentives for rooftop gardening.)

Storm water run-off is a big problem in urban areas. Cities are typically large impermeable
spaces that don't allow water to drain into the ground. During heavy downpours the sewer
systems become overwhelmed, which leads to flooded streets and basements.
Rooftop gardens act like sponges and absorb lots of rainwater. Of course, green roofs
hold the most water, but even rooftop container gardens help mitigate the volume of run-off.

Another urban problem is the heat island effect. The immense volume of concrete, steel,
and asphalt absorbs and releases radiant heat, which can raise and maintain summer
temperatures at unbearable levels. Cities can be ten to twenty degrees warmer than
similarly situated rural areas. Plants cool the air by transpiration (release of water vapor
through leaf stomata). All plants are like mini air conditioners in summer. It's the reason
lush, green grass always feels cool between the toes.

Plants absorb the sun's energy and convert it into growth, flowers, and fruit. This is in stark
contrast to concrete and asphalt which absorb the sun's energy only to release it as convective heat. Gardens not only keep the rooftop and surrounding areas cooler but also the building underneath. Green roofs are excellent insulators and have been shown to reduce annual energy consumption (both heating and cooling) by up to 15%.1

Plants are also great filters. The leaves remove pollutants from the air, while the roots filter
water and soil. Their ability to hold and bind pollutants while releasing fresh air makes plants
the perfect addition to urban areas. Rooftop gardens convert some of the dirtiest air into pure
oxygen to the benefit of all city dwellers, human and animal.

Wildlife appreciates rooftop gardens, in general. They are oases in what can appear to be a
lifeless urban desert. The flowers of rooftop gardens provide nectar for bees, butterflies, and hummingbirds, all of which have a tough time finding food in a city. The flower nectar keeps the pollinators alive and they help us by visiting tomatoes, peppers, apples, oranges, etc. so
that we can harvest fruit. Robins, finches, dragonflies, and mosquito-catching spiders are just
some of the other animals that visit rooftop gardens.

Economically, rooftop gardening can extend the life of your roof. Green roofs are more durable and estimated to last approximately 40 years as compared to around 10 years for
typical roofing. It costs more initially, but is much cheaper in the long run. In addition,
because of the numerous environmental benefits, many cities offer tax incentives to rooftop
gardeners.

Rooftops are the new backyards, a literal sanctuary in the city. A place for people to escape
the hustle of the city and relax while cutting some flowers or picking some herbs.
Urbanites can have their own "yards", even if we have to go up.

wemoss.org 2009, Last Updated July 1, 2009