World's largest urban farm to open on a Paris rooftop | Hacker News Reader

World's largest urban farm to open on a Paris rooftop

theguardian.com

60 pointsgalfarragem26 comments

Wouldn't the plants/fruit/veggies suck up pollutants ? I'm not sure I'd eat anything that grew in contact with Paris air. Last time I went there my throat and nose itched from the pollution, it never happened to me before, not even in LA.

Yes however, (anecdotally) the plants don't let the pollution get into their fruits.

Would there be pollution simply from air contact? I can't answer that question. I would assume it is still be better than pesticides and industrial agriculture?

Pollution gets into leaves and in the fruits. Question is whether it will make it unsafe for humans, probably not, but it still can affect the plant's health and the amount of crops that you can harvest.

"Tomato, watermelon, squash, potato, string beans, snap beans, pinto beans, tobacco, soybeans, cantaloupe, muskmelon, alfalfa, beets, sunflower, carrots, sweet corn, gourds, green peas, turnips, grapes, peaches, and strawberries are some of the more susceptible crops to air pollution damage. Cucumbers, pumpkins, and peppers are less susceptible. Watermelon and squash are the most sensitive of the cucurbits followed by cantaloupe."

https://extension.umd.edu/learn/air-pollution-effects-vegeta...

Thanks for that link.

There could be two saving factors:

- pollution would tend to stay closer to ground level, rooftop being less affected

- not using pesticides and other chemical can offset the pollution they’re exposed to

??? I never felt pollution like you described, having lived 23 years in Paris. You might be extremely sensitive to pollution. And I am especially surprised that you claim LA is less polluted, considering that public transportation is much less developed there.

I assume the ocean wind + wide streets of LA makes it easier.

After morning/evening rush hours Paris tiny streets are a death trap to me. I was born and raised in a small mountain town though, my body isn't made for Paris.

I checked right now and the LA Air Quality index is at 60 meanwhile 44 currently at paris.

That’s just one snapshot. In terms of motor vehicle exhaust:

NO2 in Paris is 5 right now, but it was 151 a few days ago. https://aqicn.org/city/paris/

NO2 in LA is 4 right now and peaked at 25 over the same time period. http://aqicn.org/city/losangeles/los-angeles-north-main-stre...

PS: Condescending all air quality into a single number is still useful, but does represent the subjective experience of different areas as well.

As an ashmatic, the best indicator for me is the fine particules(particules fines in french), emitted by the combustion vehicules. NO2 in Paris was 151 a few days ago, but only on one of the probes.

It is mainly a diesel / gasoline thing. There are often many more fine particulates in the air in EU cities, although with the newer Euro standards having ever larger effects, that gap is dropping rapidly. FWIW, I and many people I know experience the same thing whenever we return to Europe from longer periods away.

Lets see, the fine particles of soot you get from wood or coal fires aren't going to get into the plant, or are the fine copper particles from people's brake pads. Nor will carbon monoxide, nitrous oxide, or sulfer dioxide. Most sorts of pollution that can make you sick from eating vegtables exposed to it will kill you super dead if you breath it in. One obvious exception is lead which can accumulate in soil over the long term so make sure you don't get your urban garden soil from an abandoned lot which hasn't been tested for lead levels. Also some radioactive isotopes of things like iodine can be concentrated in plants but the ones that come to mind as doing that, like iodine-131, have half lives on the order of days to weeks so that's mostly just a concern if there's been a recent reactor meltdown or nuclear attack in your area.

> the fine particles of soot you get from wood or coal fires

I'm pretty both coal and wood fires are banned in Paris. For wood fire, I think it's fairly recent (one or two years ago) and it's an application of a directive from the EU.

Open fires are banned, but the automobile particulate mix (tire & brake wear + exhaust) and fuel-powered heating do generate a fine soot I find on my bicycle, though nowhere near as much as 30 years ago.

A quick wash and my Paris balcony tomatoes are safe and delicious !

However I remember seeing studies by Italian television which showed that fruit markets in cities had very high levels of pollutants that stuck to their surfaces. This was related to how busy the road in front of the fruit market was, but will be compounded by the long grow period. So the produce will need to be cleaned very well.

Aren't you always supposed to wash fruit/vegetables before eating anyway?

The issue is how much actually comes off when you wash them. There were vegetable rinsing aids on the market for a short time. Some compounds like to stay put.

What exactly is an urban farm?

Does it have to be on buildings? This is an area near my hometown, it has good public transport (the next Metro stop is a bit of a walk but you could take the light rail) https://www.google.de/maps/@49.4845803,11.0337896,15z/data=!...

These are all greenhouses and vegetable gardens.

This is Westland “Food Valley” it’s between Den Haag and Rotterdam ... https://www.google.de/maps/place/Westland,+Niederlande/@51.9...

Is this an urban farm? Is there any advantage to growing vegetables on a roof instead of next door?

I think the benefit of rooftop gardens is taking what is essentially "wasted" space (where I live most rooftops go completely unused) and repurposing it into something productive.

Having attempted growing vegetables on the rooftop of a 6 story building, I discovered that preparing and cleaning the roof is incredibly energy intensive. You have to bring soil from some soil farm to the city and then onto the roof of a building where you have special beds setup and a way for runoff to be cleaned and processed. Water, nutrients, tools, everything else has to be brought up there. Dust blown off the beds when it gets a bit dry flies all over the city. It also gets too hot up there because the roofs are super hot, so you need more water. Then the birds, squirrels who are actually able to climb as high as necessary, neighbors who live below the roof, and other problems creep up that were totally unexpected. Good luck to many others who will try the same and find out this on their own.

It sounds like they're using aeroponics where possible. Of course that still requires energy, but much less so than growing in soil. There's also much less overall water use, because it's essentially a closed loop system with minimal evaporation.

“Our guiding principle with all our farms is to help foster environmental and economic resilience in tomorrow’s cities,” says Hardy, who expects the farm to start making a profit within its first year. “If we can create a model that is commercially viable, rather than having to rely on goodwill and subsidies, that will help urban farms to become sustainable in their own right.”

It will be interesting to see if this succeeds economically.

I'm not sure if the amount of extra engineering and costs involved to support low rise rooftop farming is better than the opportunity cost of slapping on a bunch of solar panels. This might be a viable model for Paris due to severe zoning height restrictions, but when I think urban farms that solves big problems, I think of high density vertical farms.

How much extra weight are roofs typically built to hold? Is it safe to load them like this considering the extra weight of soil and water that soil can capture, and say a layer of snow over all of that in winter?

They say they are doing aeroponics, so soil is replaced by much lighter plumbing...

How much weight does the roof have to hold to support all that?

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