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Sunday, March 21, 2021


Keywords: food, food security, food production, urban areas, horticulture, urban horticulture, soil-based horticulture, controlled environment horticulture, urban agriculture, research, city, Sheffield, UK, United Kingdom, Great Britain


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Parole chiave: cibo, sicurezza alimentare, produzione alimentare, aree urbane, orticoltura, orticoltura urbana, orticoltura basata su suolo, orticoltura in ambientale controllato, agricoltura urbana, ricerca, città, Sheffield, Inghilterra, Regno Unito, Gran Bretagna


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Ooooh, hello dear English speaking-reading-hearing listener, welcome back to me, @sciencemug, the blog/podcast/twitter&instagram accounts/entity behind the unsuccessful e-shop stuffngo on which tells you science stories while studying a lot for a degree in “How to read Icelandic volcanoes names without making your tongue need to get into therapy and your brain start working hard on a de-evolution five-nanoseconds plan, aaand which talks to you thanks to the voice, kidnapped via a voodoo-wireless trick, from a veeery very very dumb human. Aaand which does all of this in English-question-mark, a language that is to proper English what a record-breaking snowstorm in NY this winter is to something disproving global warming. 

Today I’m gonna tell you a story about urban areas and food production!

Vegetables in a supermarket stand
Veggies and the urban horticulture style (by @sciencemug)
pic by Scott Warman is a free one (source: Unsplash); adapted by @sciencemug]

In assessing the potential of urban horticulture (UH) as a concrete source of food for urban areas inhabitants, a bunch of researchers of the University of Sheffield, England, UK, lead by Dr. Jill L. Edmondson, build a case study by which they show that there is way enough land available within the city of Sheffield to feed its people with all the fruit and vegetable they need. Dr. Edmonson and colleagues - aka the E-Science-Pack – then publish

their research (Edmonson et al, 2020; P) on the science journal Nature Food. 

Now, dear listener, before going on with the tale of the E-Science-Pack’s work, let’s provide some contest, here, ok? Otherwise many things will be unclear.

First of all, you’re probably asking yourself what urban horticulture (UH) be, right?

Well, let’s start with the term horticulture. Horticulture is that part of agriculture that growsfruits, flowers, vegetables [but also] spices [like “black pepper, cardamom, ginger” (ref)], [and also] tuber crops [like potato, sweet potato, sweet beat, cassava (ref)], [and also] mushrooms, bamboo, plantation crops [like “coconut, cocoa, cashew, oil palm, coffee, tea, rubber” (ref)], [and also] medicinal and aromatic plants [like aloe, angostura, arnica, basil, belladonna, carob, cinnamon, Curcuma longa, mace, licorice, rosemary etc etc (ref)]” (ref). 

So, now that we know what horticulture is, since the study of Dr. Edmonson and colleagues is ‘bout urban horticulture, let’s define what “urban”, for the notoriously precise and accurate research people, actually mean.

Well, with “urban areas” the science people mean areas that “consist of predominantly human-made surfaces, have high concentrations of people, and are the hub of economic activity” (1). 

So, dear listener, in the end, urban horticulture is horticulture made in urban areas, that is, in super-short, basically the cultivation of veggies and fruits within a city. 

Now, the E-Science-Pack, in its study, explores two kinds of urban horticulture: the soil-based horticulture (SBH), and the controlled environment horticulture (CEH). 

Aaaaah” I can hear you violently screaming, dear listener for the sake of the mighty BND, the Book of Never-ending Definitions! What are those two now?!”.

Eh, I know, I know, pal, I’m sorry, I guarantee you we’re almost done with the definitions and premises, but without ‘em the story of the city of Sheffield and its potential urban grown food won’t be that clear at all... 

So, as just said, urban horticulture can be soil-based (SBH), and/or practiced on controlled environment (CEH).

The soil-based urban horticulture is the urban horticulture done within green infrastructure, that is places likeparks, gardens, roadside verges and woodland”, (P) so, you know, green areas.

The controlled environment urban horticulture (CEH), instead, is the one performed on flat roofs within gray infrastructure, that is, for instance, on the flat roofs of commercial and non commercial buildings (P). Unlike the soil-based one, the controlled environment horticulture doesn't need soil, or much of it, since, for instance, we’re talking about hydroponics (that uses water as the growing medium instead of soil (2)), and aquaponics, a system that integrates aquaculture (that is fish farming) with hydroponics in so creating “symbiotic relationships between the plants and the fish; [aquaponics, indeed,] uses the nutrient-rich waste from fish tanks to “fertigate” hydroponics production beds; and hydroponic bed cleans water for fish habitat(2). 

Oooook! Now that we’ve compiled our glossary and explained the basic terms, let’s cut to the chase of the E-Science-Pack's research.

Dr. Edmonson and colleagues’ work basically aims to understand the potential of urban horticulture as a provider of food security for people living in urban areas.

To address this issue, the E-Science-Pack chooses to build a case study about the English city of Sheffield.

Sheffield, indeed, is a good choice for a case study of such a kind. It is the sixth most populated city in England and Wales (about 580-thousands people, more or less like half Milan, or half Dallas). And, above all, Sheffield population is likely to suffer some level of food insecurity (3), as the city, being this typical of larger urban areas, belongs the most deprived 25% areas in England, according to the Index of Multiple Deprivation (IMD) that measures “how deprived an area is by identifying the degree to which people are disadvantaged by factors such as low income, unemployment, lack of education, poor health, and crime” (4).

A boy and a man gardening
The difficulties of urban horticulture (by @sciencemug)
pic by CDC is a free one (source: Unsplash); adapted by @sciencemug]

So, once identified a target city, Sheffield, the E-Science-Pack first wants to understand the “potential productive space” (P) of urban horticulture, that is how much land, within the city, could be used for both kind of urban horticulture (that are, as above said, the soil-based one (SBH), and the one practiced on controlled environment (CEH)).

To calculate how much land there is in the city of Sheffield for hurban horticulture, the researchers consult the local authority boundary and collect data from two high-spatial-resolution datasets: the Ordnance Survey MasterMap which provides a “detailed and accurate view of Great Britain's landscape – from roads to fields, to buildings and trees, fences, paths and more” (see), and the Google Earth Imagery.

The E-Science-Pack then uses these data in a Geographic Information System (GIS) to map the green and gray above mentioned infrastructure in Sheffield.

And if you’re wondering what a Geographic Information System be, well, dear listener, a GIS is “a tool that can process, display, and integrate different data sources including maps, digital elevation models [...], GPS […] data, images, and tables” (see here: download Chapter 18). So, in short, GIS data models provide a representation of how the actual world looks. 

So, after collecting and elaborating aaall these data, Dr. Edmondson and colleagues know what follows, about Sheffield.

The city covers an area of 368 square kilometers (like, more or less, Detroit, or roughly a third of Honk Kong or Rome). Of these 368 square kilometers, 227 are urban or peri-urban, comprising green and gray infrastructure (P) (oh, and peri-urban areas, dear listener, are those areas “that surround [...] metropolitan areas and cities – [but are] neither urban nor rural in the conventional sense” (ref), in short peri-urban areas are the buffer zone between city and country, a zone in transition). 

At this point the E-Science-Pack starts with the soil-based urban horticulture assessment.

The researchers find two things. First that the whole Sheffield green space covers 45% of the city (more than 10 square kilometers), and this is a percentage in line with the rest of the cities in the UK, and second that Sheffield green infrastructure is mostly located in its suburbs (that can be defined as “lower density areas that separate residential and commercial areas from one another(ref)).

Now, the 38% of Sheffield's green infrastructure is made of private gardens, which are clearly not always used for soil-based horticulture.

1.3% of the land of Sheffield's green infrastructure is instead made of urban allotments, which are plots specifically destined to be used for horticulture by individuals or households, and that UK authorities, like those of other countries in Europe, are legally required to provide for rent to enlisted citizens who ask for them (as a matter of fact, urban allotmentsare, in terms of area, one of the main resources for UH in the old continent (P)). 

So, Dr. Edmondson and science pals properly set and put at use their above mentioned Geographic Information System, and by doing that they identify extra land, within Sheffield's green infrastructure, that can potentially be used for soil-based urban horticulture, but it’s not at present.

This extra land consists of parcels split into community garden spaces, and further allotment spaces. The community garden spaces are smaller (the parcel size ranges from 6 hundreds to 3 thousand square meters), while allotment spaces are bigger than 3 thousand square meters (which are about 1.5 times the floor area of the famous Hugh Hefner’s Playboy Mansion in Los Angeles, just to have a benchmark, you know...), aaand these allotment spaces are formed by groups of plots with an average surface of 250 square meters.

Now, in the end, putting aaaall these different types of usable surfaces together, the E-Science-Pack, with its survey, finds that, all in all, each person in Sheffield potentially has 98 square meters (321,52 square feet) of land available for soil-based urban horticulture.

Of course, the researchers admit, this represents an upper estimate, since chunks of such an identified suitable land for sure would not be usable in reality. Plus growing green stuff on, for instance, domestic gardens could suffer “disproportionate losses to infrastructure (access, storage)” (P).

Nevertheless, Dr. Edmonson and colleagues underline that even if the Sheffield people could actually use just a quarter of those 98 square meters per capita they potentially have at disposal for urban horticulture, weeell, each of them would end up cultivating the same amount of land “per capita nationally used for UK commercial horticultural production of fruits and vegetables(actually, even a bit more: 24.5 vs 23 square meters) (P).

So, dear listener, to sum up, the first result of the E-Science-Pack study is to show that each and every one of the people living in a common mid-large English city like Sheffield could practice soil-based urban horticulture on a piece of land which surface is from 1 to 4 times as large as the one that the industry of horticulture in Great Britain currently uses per capita.

And this are just the findings about soil-based horticulture performed on green infrastructure.

What does the E-Science-Pack digs up about the other kind of urban horticulture, the controlled environment horticulture (CEH) that is doable on the flat roofs of Sheffield's gray infrastructure? 

Eheh! The answer, dear listener, after the commercial break! 


Did you always want a garden so beautiful and lush that the Gardens of Versailles are indeed the result of the fact that Louis XIV travels in time (as the result of a sick twist in a yet to be even thought sequel of Back to the Future, “Back to the Future XIV – The mess royal!”) and then he, Louis XIV, sees your garden and says “Parbleu! Le roi d’Amerique etait orange!” ‘cause from your garden he can see your tv tuned on the news, and then he’s tazed by your well-meaning but a bit too nosy neighbor who’s strangely always close to the fence when your wife is sun bathing and who (the neighbor) thinks he (meaning Louis XIV) is a lunatic escaped from the psychiatric ward of a nearby institute, and then he (again meaning Louis XIV) as a consequence of the shock forgets who he is, becomes a gardener, does your garden, and then trips on the hose, hits his head on the border made of fake Kentucky stones of a little pond he himself has designed, regains consciousness back in his time, thinks it has all been an odd but humbling dream, decides “the hell humility, I’m le Roi Soleil”, and so he wants a palace with gardens waaay better than the one he did for you since, in the end, he was a really crappy gardener and, as a king, he can afford real top-notch professionals unlike you cheap wannabe?

Green Thumb Liquors sign (by @sciencemug)
"Green Thumb Liquors" store's sign (by @sciencemug)

Well, look dude, to be honest, at this point I actually lost my train of thought and I can’t remember anymore what this commercial is about, sooo, aaa-wkward… Oh oh! Wait a minute... I think it was maybe something related to plants… Uh. Ok. Let’s just say something like this: if you don’t have the green-thumb but wants one, provided you can’t cut one out of Hulk’s hand for obvious reasons (for reference watch first the classical Lou Ferrigno tv-show from the ‘70s, and then the Marvel's movies, while you can serenely skip the Eric Bana's and Edward Norton's ones) if you don’t have the green-thumb but want one, well, we sell nice green markers, just around the corner! Actually we sell markers of all kind of colors. And liquors! Yeah, those too. Yup... Ok, ok, we don’t sell markers, we just sell liquors. But hey, buddy, trust me when I say that, after all that gardening nonsense, well, it really looks like you can use some booze... And then more!


Sooo, dear listener, back to the E-Science-Pack and the controlled environment urban horticulture (CEH) doable on the flat roofs of Sheffield.

Dr. Edmondson and colleagues with their research find that the commercial city centre area of Sheffield is 2.3 square kilometers large, that buildings cover 58% of such an area, and that a quarter of this building area is in turn covered by flat roofs (we’re talking of a surface as wide as about 32 football fields) (P).

The E-Science-Pack, of course, is aware that not all flat roofs are usable for controlled environment urban horticulture, so the 32 football fields are an upper limit. 

Moreover, dear listener, this upper limit corresponds just to half a square meter per person, meaning each Sheffield's citizen could potentially have at disposal as much space as that covered by a very small storage closet, top, to practice controlled environment urban horticulture.

Now, at a first look, this doesn’t seem much at all, I agree with you dear listener, but you’ve to consider some facts. First: controlled environment horticulture, could allow a year-round cultivation by employing greenhouses, and rainwater for irrigation. Second: its production systems (like the above mentioned hydroponics and aquaponics) have a very high-yielding nature. Third: controlled environment horticulture focuses on producing a smaller number of high-value, high-yield crops. Take tomatoes, for example: the average yield of hydroponically grown tomatoes is 42.9 kg/per square meter/per year. Given this, if just 1 out of 10 of the flat roofs found in Sheffield by the E-Science-Pack’s study were actually used for tomato production via CEH, well, dear listener, then “it would be possible to grow enough tomatoes to feed nearly 2% of the [Sheffielders] per year on a 'five a day’ diet (P) which consists in eating a minimum of 400g of fruit and vegetables a day, specifically 5 portions of fruit and veg in total, not 5 portions of each [with a] portion of fruit or vegetables [being] 80g” (see). The ‘five a day’ diet, by the way, is a diet advised by the World Health Organization (the WHO) (advise fully accepted by the same British National Health Service, the NHS) “to lower the risk of serious health problems, such as heart disease, stroke and some types of cancer” (see). 

So, to give enough tomatoes to 2% of the people of Sheffield means to satisfy the healthy diet of thousands. But it gets better. According to Dr. Edmondson and colleagues, indeed, if the amount of Sheffield's flat roofs used for controlled environment horticulture were 75% instead of the just above considered 10%, then the number of Sheffielders provided with enough tomatoes for a ‘five a day’ super-healthy diet would rise six times, from 2% to 12%. (P).

Now, dear listener, if you’re wondering why the E-Science-Pack precisely thinks about tomatoes, well the answer is ‘cause the UK presently imports almost 90% (86%) of its total tomato supply, “and this crop alone accounts for [more than one fifth (21%)] of the value of all vegetable crops imported to the United Kingdom(P). 

So, dear listener, if you put together aaaall these facts, you see that controlled environment horticulture can give an actually sensible contribute to the potential of urban horticulture as a whole. 

And what’s this whole? What are the final numbers of urban horticulture?” I guess you’re asking out loud while brandishing a bunch of half gone veggies and rotten fruits ready to throw ‘em at my voice if I don’t answer properly?

Weeell, dear listener, I’ve just finished giving you the numbers of controlled environment horticulture, as for the numbers of the other branch of urban horticulture, the soil-based one, well, here they come!

Dr. Edmondson & colleagues consider that with a quite probable average yield across all allotment land of 1.8 kg/ per square meter/ per year, then soil based urban horticulture can feed 3% of Sheffield's population a ‘five a day’ diet.  

Now, dear listener, if you add up the existing area of allotments and domestic gardens, and potential new allotment and community garden sites of Sheffield, well then this total surface is almost 6 square kilometers (5.752) wide.

And the E-Science-Pack says that if all this land (the 100% of it) were used for soil based horticulture, then this could grant a 5 a day’ diet to more than 7 hundred-thousand (709) people per year, namely the 122% of the population of Sheffield. 

Three tomatoes chatting
Tomatoes-tomahtoes & the hidroponics (by @sciencemug)
pic by Ioan F is a free one (source: Unsplash); adapted by @sciencemug]

But, of course, I’m with you dear skeptical listener, a full exploitation of the land of Sheffield's green infrastructure is rather unrealistic. So, the E-Science-Pack elaborates a more realistic scenario, where soil based horticulture is practiced only “in 10% of domestic gardens and expanded into 10% of the additional land identified [by their research]” (P). Well, dear listener, with these percentages of green infrastructure land use, the soil-based urban horticulture could feed 12% of Sheffield’s population per year.

So, if you add up this possible scenario (12% of the population fed), with the present actual production of the allotment land now in use (the above mentioned 3% of the population fed), you see that soil-based urban horticulture alone, each year could fill the stomach of almost one of Sheffield inhabitant out of six, with all the vegetables and fruits he/she needs for a healthy diet.

Nooow, dear listener, I am a dumb brainless blog/podcast, but I can clearly foresee the questions/objections you’ve at this point:

- yeah, yeah, it’s all a beautiful green-color movie with unicorns and Bambi and their offspring Bambicorns and edible low-calories rainbows and broccoli that taste like chocolate, and so on. But how many people in Sheffield should have the green-thumb to carry on the E-Science-Pack’s scenario, and how much work should these people put on cultivating their piece of green and gray infrastructure to achieve the target production the E-Science-Pack refers to?

- Plus, hydroponics and aquaponics systems, and greenhouses, and rainwater recovery structures and so on, all on roofs, indeed the whole controlled environment urban horticulture deal sounds pretty complex to be actually feasible, don’t you think?

- Plus, ok Sheffield and the case study, but is urban horticulture something that can actually work, in reality, if not in every, at least in most of the presently existing urban areas?

- Plus, well, I’m still thinking about this, let’s skip straight to the next one.

- Finally, ok, cool, let’s invest time and money and hard work so to be able to cultivate urban land and grow food for the people of the cities, but, you know, is it really necessary? Why can’t we simply go on like we’re doing now and let the food industry and commercial horticulture do the job of putting food on people’s tables? 

Weeell, dear clever listener, yours are all good points, aaaaaand you’ll read/hear the answers to them in the next part of this post/episode!

But before leaving you with the powerful itch all over your cerebral cortex I’m sure you feel at the end of each part of every multiple part post/episode I do, well, let me finish, as a sneak peak to the answer to your last question, with the opening statement of Dr. Edmondson and colleagues' research paper: “food insecurity is a growing issue in the Global North where the majority of the population (sometimes in excess of 80%) lives in urban areas” (P). 

Ooook, till next time pal, and if you spare some time and feel like doing it, please subscribe and/or rate this podcast, and/or leave a comment on the blog, and/or take a tour on my stuffngo (sNg) e-shop on so you can see if there’s something you like, aaand/or make a donation clicking on the "Donate" button on this dumb blog’s home page!



The paper this post is about (P)

- Edmondson, J.L., Cunningham, H., Densley Tingley, D.O., Dobson, M.C., Grafius, D.R., Leake, J.R., McHugh, N., Nickles, J., Phoenix, G.K., Ryan, A.J., et al. (2020). The hidden potential of urban horticulture. Nature Food 1, 155–159.



1- Martellozzo, F., Landry, J.-S., Plouffe, D., Seufert, V., Rowhani, P., and Ramankutty, N. (2014). Urban agriculture: a global analysis of the space constraint to meet urban vegetable demand. Environ. Res. Lett. 9, 064025.

2- Al-Kodmany, K. (2018). The Vertical Farm: A Review of Developments and Implications for the Vertical City. Buildings 8, 24.

3- Smith, D., Thompson, C., Harland, K., Parker, S., and Shelton, N. (2018). Identifying populations and areas at greatest risk of household food insecurity in England. Applied Geography 91, 21–31.

4- The Area Based Analysis Unit, O. for N.S. 1 (2009). Understanding patterns of deprivation. Reg Trends 41, 93–114.

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