In urban areas with limited space, rooftops are a popular choice for not only
outdoor gardens and farms but also indoor farms.
Beyond the obvious space advantages to rooftop farming, there are several other reasons why rooftops are more advantageous for agricultural production.
Urban agriculture implementation will have different limits in different geographical areas of the world.
As the world population residing in urban areas is projected to nearly double by 2050, these trends will become increasingly vital to fresh food production in urban areas.
Depending on the type of growing medium you are using, agricultural units on urban roofs can retain up to 90% of rainwater which can in turn increase production and growth without constant manual watering or time consuming set up of self watering systems.
Depending on your location and the type of crop you are growing on your roof, this water access and retention capability may be a huge advantage for your crop growth.
precipitation per unit area across the world, 1961-1990
As previously mentioned, rooftops are first and foremost ideal for urban agriculture due to their space potential. According to American Rivers, there is over 4.85 trillion sq ft of roof space in areas with populations above 50,000 people in the United States alone, and currently less than .1% is utilized, despite over 25% growth year over year for urban agriculture on rooftops since 2010.
One special note to keep in mind before starting your rooftop urban farming project: Green Roofs for Healthy Cities suggests that the majority (perhaps as high as 95%) of current roofs are strong enough to support a full scale urban farm with all of the necessary growing medium layers (image below).
Interested in growing on your roof but not sure about your roofs stability? Talk to our friends at Recover Green Roofs.
urban farming on the surface of the roof itself usually requires special support (source)
Since the beginning of agriculture, pests have been a continual and evolving challenge for growers. Pests *will* still be a risk on rooftops (rodents, birds, common insects) however, rooftop plants will be inaccessible by larger urban animals like rabbits or even deer. Additionally, rooftops will be less susceptible to disruption from human traffic. As far as limiting insects with your urban rooftop crops, the first place to look for a solution may be bolstering the health of your soil or growing medium.
pests like rabbits will be less of an issue on rooftops (source)
Urban and greenhouse farming research from the University of Massachusetts at Amherst points out that maintaining horizontal air flow in greenhouses with the use of fans is important for improving quality of the products grown in the greenhouse. Depending on the geographical location of outdoor urban rooftop farms, natural air flow conditions may provide similar benefits to crop production that fans would provide in a greenhouse. According the UMass research,
"During daylight hours, photosynthesis depletes the carbon dioxide that is in the boundary layer of air next to the leaf. Moving air will replace this depleted air with fresh air having a higher carbon dioxide content".
The effects of urban noise may be beneficial for rooftop plants. Source
Botanical studies from as early as 1962, have shown that ambient sound can have a positive effect on the production of agriculture. In fact, the difference in plant health between those grown with sound and those grown without sound has in some instances not even been close, with plants cultivated in the presence of ambient sound having growth acceleration in excess of 20% and increased biomass of 78%.
But how much more sound is present on an urban rooftop than a rural plot of farmland? According to Engineering Toolbox, the level of audible sound in rural wilderness areas tends to average to about 30-40 dBA whereas average sound levels in urban areas will usually approximately 85-90 dBA .
Olive Tree's with yellow sky and sun, Vincent Van Gogh, 1889 source
One key advantage of rooftop growing is access to sunlight. On the street level or indoors, light can be a serious issue and deficiency for urban crops.
For these reasons, urban rooftops may be the best place to start with an urban farm, as plant's will have the maximum possible access to natural sunlight, and this will directly increase yield.
and that's not all: because of the warmth provided by this extra sunlight exposure, rooftop urban farms will often have a "season extension" effect, meaning you can start growing slightly earlier in the spring and grow slightly longer at the end of autumn.
Explore other small-scale urban agriculture tips and tricks at urbanvine.co/blog
At the request of some readers we've added in a couple cons to rooftop growing:
1) Weight: some roofs will not be approved for the weight required to make rooftop growing viable
2) Zoning: Some roof spaces will prohibit certain or any activities on building roofs. Check with relevant property authorities before making any building plans!
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