Some rooftop farming background

I just posted a brief FAQ about what being a PROOF “farm host” for 2010 will entail. Of course the most important question is, “Does farming on rooftops work?” The answer…we sure as heck hope so! In addition to the fact that Nelson Mandela farmed a rooftop pretty successfully when he was in prison, and that rooftop farming has become enough of “a thing” that it recently was featured in a rooftop farming article in the New York Times, a few recent rooftop farming projects have popped up to show us it can be done. For example (all these links will open in a new tab or window):

— Check out the world’s first Rooftop CSA (as far as we know), built and farmed by Erik in Milwaukee.

— There is a rocking rooftop farming project in Chicago.

— Community organizations have been successfully farming rooftops in Montreal for years.

— This edible green roof in Brooklyn is amazing. (PROOF will be growing in planters rather than in green roof material, but this farm is still really great.)

— Some companies like Sky Vegetables have been growing on rooftops on a large scale by installing greenhouses and other great systems.

— There are also a few small for-profit ventures like My Farm in Berkeley that build farms in people’s backyards, much like PROOF wants to do on Philly rooftops.

Also, you can find great rooftop farming and other urban agriculture information at’s rooftop gardening page,’s guide to setting up your own edible rooftop garden, and’s International Rooftop Gardening Projects page.

Let us know if you find any more inspiring links.

Want to host a rooftop farm in 2010?

Recently word about PROOF has slipped into a couple of eco-friendly e-mail newsletters and people from around Philadelphia are contacting us with questions about how to become farm hosts for our experimental 2010 season (March to November). Yes, we are still accepting volunteers! PROOF has a good number of roof volunteers, but we could always use more. Most of our roof volunteers are in West Philly but we’ve been fielding questions from all over the city and plan to find some way to work in some capacity with everyone.

For those of you interested in volunteering your roof, here are the basic things you need:

1) a flat roof. The whole thing doesn’t have to be flat, but a good stretch of it should be.
2) reasonably easy access to that roof (via a door, roof hatch, out a window or other means of access that doesn’t require exterior ladders…though maybe a ladder going up one story is okay.)
3) a willingness to let PROOF staff and/or volunteers into your house two times a week (up to three times a week during peak growing season), so we can farm the produce
4) a positive attitude and an eagerness to work with PROOF throughout this experiment.

We’re interested in talking with renters but we’ll definitely require the owner’s written permission.

As a PROOF farm host (as long as we get a decent amount of grant money to pay for all this stuff 🙂

— A free roof evaluation by Cory Suter of Bioneighbors, a sustainable roofing company. (normally worth $100)
— Free planters, potting mix and plants, as well as free installation of your farm by PROOF volunteers (planter, mix, plants and installation an estimated value about $1000 per roof).
— Free maintenance of your farm by PROOF staff (estimating two visits a week from March to November to plant, care for and harvest produce, maybe three in the peak weeks)
— Free produce from spring to mid-fall of 2010. PROOF will try to give you at least a decent boxful of fruit and vegetables per week, with a bit less in the spring and fall and a bit more in the summer. We say “try” because the rooftop farm is in its first year and it’s therefore all an experiment, but we’ll do the best we can. (average value of a CSA – community supported agriculture – farm share equal to about what PROOF hopes to provide, $600)

Still curious? Some quick answers to quick questions:

— Q: Is this a “green roof” system?
— A: Not really. PROOF will be installing planters on your roof but won’t be putting soil or waterproof membranes on your roof, as are typical in a “green roof” installation. Green roofs are awesome though and if you want one, by all means do it!

— Q: Will the planters hurt my roof?
— A: PROOF is designing planters that will span party walls (the brick walls of your house that connect with the house on the row next door) so planter weight rests on them, not directly on your roofing material. We’re working on solutions for detached houses or twins.

— Q: What if I don’t have a hose bib upstairs?
— A: PROOF should be able to either run a hose up from a hose bib you may have on your first floor or use an adapter to get water from an upstairs sink.

— Q: Who pays for the water?
— A: Farm hosts do. PROOF is designing its planters to be self-watering, which greatly reduce water needs. Planters will also capture rainwater, so in rainy weeks or for a couple days after a thunderstorm we probably won’t have to add water at all. We’re planning to work with rain barrel collection projects to also enable the planters to be able to use as much rainwater as possible.

— Q: Won’t the soil dry out?
— A: PROOF is using self-watering planters (more on those in another post) that have covers — the plants grow up through the covers. Being covered, the planters don’t dry out and also don’t allow for much evaporation. Hence, the soil stays moist.

— Q: What can be grown on a roof?
— A: Almost anything that grow in the ground. There are exceptions, of course, though on the other hand some things grow particularly well in containers. As for what you can grow on your particular roof, PROOF will work with roof hosts to tailor a planting scheme to the fruit and vegetables you like to eat.

— Q: Do I have to keep the farm permanently?
— A: Nope. PROOF would love you to keep the planters after 2010 so we don’t have to dismantle them haul them down, but we don’t require that kind of commitment.

— Q: How much work do I have to do on the farm?
— A: None, if you like. Your main responsibility is to let PROOF volunteers into your house at the agreed-upon times. Of course you can absolutely participate in the farming to the extent you want. (We may also ask you to spritz the plants with water on hot days, or let a PROOF staffer in to do it for you.)

— Q: How much produce will I get?
— A: PROOF will try to provide your house with the equivalent of 1/2 to 1 full CSA share of produce from your roof. We will distribute excess by selling it at farmstands or in some other way. This will be one way PROOF will support its future operations. (PROOF is a non-profit but still needs money for infrastructure).

— Q: Will the produce be organic?
— A: PROOF won’t have organic certification in 2010, but everything used from potting mix to fertilizer will be organic.

— Q: What if I don’t have access to my great flat roof?
— A: PROOF is working with green roofers who install roof hatches. We’re hoping to be able to help financially if you want to do that.

— Q: How much will this all cost me?
— A: If PROOF gets grants and donations this fall to support the project, zero. If we don’t….we’ll talk.

Please let us know if you have any other questions and we’ll try to make up answers.

It’s like a forest up there

Here are a couple photos of the pretty encouraging plant growth on our roof at 44th and Pine, starring almost-five year old Molly and just-two year old Lily.

These plants are growing in plastic tubs that were pseudo-earthbox experiments from last year:

rooftop farming at 44th and Pine, plants in 2008 experimental planters

rooftop farming at 44th and Pine, plants in 2008 experimental planters

Up on the roof at 44th and Pine on July 1, 2009

Up on the roof at 44th and Pine on July 1, 2009

Here are tomato plants abounding in this year’s experimental planter. No root rot yet.

plants booming in 2009 experimental planters on July 1, 2009

plants booming in 2009 experimental planters on July 1, 2009

Exciting rooftop farming updates!

There are a lot of them.  Here are a few:

1. the 10 Roof Pilot project for 2010:

Response has been really great to our call for “farm hosts” for our 2010 pilot project. We have more than 10 potential hosts, with more enthusiastic e-mails coming in each day.  Over the next couple weeks I hope to check out the volunteers’ roofs and see if we do in fact have all 10 slots filled. Thanks to Gina, Tammi and Josh, Josh and Hannah, Alisha and others who have recently stepped forward, and to PROOF’s own prototype planter co-designer, Andrew, who should have a roof of his own to offer by the end of the summer.

2. Money

People have been offering money…!  Sort of.  At least, I’ve been talking with a variety of individuals and organizations about their desire to financially support the rooftop farm project.   If you are part of, or know of, a foundation or any other entity that might get behind the idea of transforming Philadelphia’s 400,000 flat roofs into viable organic farmland, drop me a line.  (

3. The University of the Arts Sky Farm

I met on Tuesday with Tony Guido and his class of industrial designers at the University of the Arts.  They’re planning to build a farm on the 4,000 square foot concrete-reinforced roof of their main building at Broad and Pine (the Gershman Y building).   We talked about working together on planter prototypes throughout the fall and winter. Ryan and Cory have also met with them over the last few weeks, so they’re definitely in on what PROOF is up to.

4. Community Design  Collaborative

This week I talked with the project manager of the Community Design Collaborative, an organization that helps non-profits with design and other kind of planning for projects just like ours.   She suggested PROOF apply to be part of their next round of supported projects.  The application deadline is July 15.  If they agree to work with us we’ll have their professional designers, architects and engineers collaborate with us over the winter to design amazing planter systems.

There’s other news, but I’d rather leave you wanting for more.  In the meantime, check out this article from about urban farming:

Have a great day

Planter update

I had a few moments this week to tackle some potential design challenges presented by our previous planter prototype.  The problem is that the potting mix is heavy and it weighs down the fabric so much that the fabric ends up filling most of the space in the water reservoir.  The fear is that too much of the mix will end up resting in water, which will result in root rot.

To potentially solve this problem I chopped up a 2’x4′ and attached it to our basic wooden frame to raise it.  I cut 16″ lengths and and ran them 10″ up the sides, so each planter is now suspended 6″ from the ground.  Check it out:

PRooF prototype planter raised on legs

PRooF prototype planter raised on legs

I then attached the fabric around the outside of the frame rather than the inside, figuring that would give it a bit more structure for it to hold the mix:

PRooF prototype planter with fabric around the outside

PRooF prototype planter with fabric around the outside

Next I placed three pond baskets (plastic baskets with tiny holes) beneath the frame and cut holes in the fabric.

PRooF prototype: pond baskets sitting beneath fabric

PRooF prototype: pond baskets sitting beneath fabric

PRooF prototype take two: fabric with holes cut in it

PRooF prototype take two: fabric with holes cut in it

Most of the mix should sit on the fabric, but some will go through the holes I cut in the fabric and rest in the pond baskets, which will sit in the water.  This will be where the mix and water meet and where the wicking will happen.  (The bulk of the mix will rest on the fabric suspended at least an inch above the water level, allowing for aeration.)

Next, I attached the pond liner, again around the outside, to act as the water reservoir.  I could have done it more attractively,  but didn’t:


PRooF prototype planter with pond liner around outside for water reservoir

After I did all this I filled the reservoir with water.  I cut a hole in the liner about 2″ up to use as a drainage level.  Everything seemed to work.

I decided not to put in the potting mix until I’m ready to plant anything, which should happen some time in the fall, but I’m pretty confident this design improves on the last one.

(The tomato plants I put in the other planter are doing really well, by the way.  I’ll take a photo of them some time.)

Building Prototype Planters

Hello Rooftop Farmers everywhere!

This is the first real update to what will probably not be the most-often updated blog in the world, but will provide a general account of the 2009 growing season’s effort to pull together a Philadelphia Roofotp Farm, which, because the acronym works, will heretofore be called “PRooF.”

So far this season several of us including Shy, Jade, Steph, Ryan and Andrew, have gathered at my house in West Philly to brainstorm and conceive everything from planters that will be great for rooftop farming to structural systems that will span rowhouse roofs and elevate planters off of roof surfaces to pulley systems that will conquer gravity and lift farm materials up into the sky.  We’ve also talked up the project at an urban agriculture-oriented Urban Sustainability Forum and made a lot of great contacts.  There has been much progress.

Over the last couple weeks Steph, Ryan, Andrew and I put our minds together to design a prototype rooftop farming self-watering planter.  I recently put the finishing touches on one and planted a bunch of tomatoes.  Here are details.

The goal:
To develop a light, inexpensive, self-watering planter than can be easily built and will function well in rooftop farming applications.  I built two 8′ x 2′ planters.

The process:


wood for PRooF's self-watering rooftop planter 2009 prototype

wood for PRooF's self-watering rooftop planter 2009 prototype

The planting tubs I used last season in the garden on my roof were made out of plastic Rubbermaid tubs.  They worked well, but from the beginning we decided we’d like to avoid using plastic.

We first thought about building our prototype planters out of wood salvaged from shipping pallets, but then abandoned the idea when we realized that the pallets were heavy — really really heavy — and difficult to work with.  So we decided to try thin, light wood to frame out the planters.  In the photo you’ll see enough wood for two 8′ x 2′ planters — four 8′ 1×10″s and one 8′ 1×12″. I bought relatively cheapo wood, not pressure-treated. It will rot over time, but won’t run chemicals into the soil.


Next, I cut the 1×12″ into four 2 ft long pieces to use as the short ends of the planters.  (why 1×12″?  aha!  You’ll see later):

8ft 1x12" cut into four pieces to use as prototype planter ends.

8ft 1x12" cut into four pieces to use as prototype planter ends.

Next, using my highly advanced carpentry skills, I screwed two planters together using exterior screws:

Frames of PRooF prototype planters, 2009

Frames of PRooF prototype planters, 2009


The next thing I did was very clumsily apply stain to the wood, inside and out, with the idea that having some stain on the wood will make it last longer. We’ll see. I forgot about the staining operation until I had the planters framed so I didn’t have proper stain-applying tools or even proper stain. I used the leftover remnants of the stain I put on my backyard fence several years ago. It came out splotchy and pretty ruddy-looking, but no one’s looking (except you).

Clumsily stainted PRooF prototype planters, 2009

Clumsily stainted PRooF prototype planters, 2009

Fancy schmancy.

At this point the sun was shining and I got hot and took off my shirt. Note to self: next time wear sun block.

shirtless farmer


Next, I took an 7′ x 10′ pond liner (epdm rubber) I bought at Lowe’s, cut it in half and stapled each half inside one of the planter frames to serve as the water reservoir.  We chose epdm because it’s strong and impermeable and is supposed to not leach any chemicals.  (we used pond liner rather than the epdm used for roofing because that epdm has UV-coating that could come off — thanks to our Milwaukee Rooftop Farmer friend for the tip.)  After I took the photo below I stapled the pond liner up along the insides of the frames.

Pond liner stapled into PRooF 2009 prototype planters

Pond liner stapled into PRooF 2009 prototype planters


The next step was to staple permeable fabric (I used weed-blocking fabric from Home Depot) around the frame to hold the potting mix. I hung the fabric over the top of the frame and stapled it on the outside of the frame so the weight of the mix would hang on the frame.

The intent was for the fabric to hang down about 7″ into the frame. Later  I drilled a hole about 4″ up the side of the frame. Logic has it, a couple inches of the mix will hang down into the water and interact with it, allowing the plants to wick the water up when they’re they’re thirsty. We’ll see if that happens.

A  likely scenario is that the constant connection between too much water and the mix, without enough aeration, will lead to root rot.   In fact, I’m kind of sure that will happen.  So what to do?  Right now, with this first generation prototype design, cross our fingers.  In the future, we’ll factor good aeration into the design and actually make things work well.  Admittedly, this is a beta version….

Why did I break the fabric into two sections in each planter? Read on, curious farmers.

Permeable fabric hanging inside PRooF prototype planters, 2009

Permeable fabric hanging inside PRooF prototype planters, 2009


For the potting mix I used the special formula concocted by master container gardener Ed Smith. Basically, it’s 1/2 compost and 1/2 a mix of peat moss, perlite and vermiculite, with some minerals thrown in to sweeten the deal (greensand, lime, phosphate, dried blood and axomite). [[There is debate over whether peat moss is an environmentally sound material to use. It really seems to be the best thing to use in self-watering containers because of the way it retains moisture. But it’s a very very slowly renewable resource — it renews over hundreds of years, if at all — and is therefore being depleted. I’ve read that less than 1 percent of available peat land is being used for commercial peat-ing, and that the peat-ers are trying to renew the resource faster than they use it — if the don’t call it “repeating” they’re sorely lacking pun abilities — but it’s still going away. I decided to use peat this year, though slightly less than Ed suggests in ratio to the compost, and try to see if there are alternatives for next year.]]

Each planter took about 1.9 cubic feet of peat moss, 160 or so pounds of compost and a bunch of perlite and vermiculite to create air pockets.

Anyway, here it is:

Potting mix in PRooF protoype planters, 2009 -- hurrah!

Potting mix in PRooF protoype planters, 2009 -- hurrah!


Covering the planters with plastic enables the mix to become a closed system — the plants drink from the reservoir when they’re thirsty but the water doesn’t evaporate. This can theoretically extend the growing season because the soil will warm up faster, but that may also kill things off because of extra heat. That’s all part of the experiment.

PRooF Prototype planters 2009 covered with plastic

PRooF Prototype planters 2009 covered with plastic

Why did I use a fancy brown tarp rather than plastic sheeting? To waste money, I guess. [At some point I’ll calculate how much this all cost, but not tonight.] Maybe one place we’ll do research is to find out for sure which permeable coverings will be best — black on top or white reflecting? plastic or something else? what covering will leach stuff and what won’t…?

And now, the answer to the question of why the 1×12″ boards and why the fabric was broken into two sections. With the 1x12s on the ends and 1×10″ sides, the plastic angles down into the middle. When rain comes, ideally the water will run into the middle, where I put the fill hole. Theoretically these self-watering planters have just become super self-watering. (There was a big rain the day after I build the planters and I think that worked.)

By this point I was super-exhausted. Luckily, planting was easy. I bought some late seasons starts from Greensgrow, cut holes in the tarp and put the transplants in. Voila — we have a farm:

Voila!  We have achieved farm.

Voila! We have achieved farm.

Thankfully, I remembered to drill an overflow hole about 4 inches up the side of the planters before going in for the night and having the mix and plants become completely waterlogged.

After all this effort, we’ll see if all the plants die.

1) Brainstorming and building stuff is fun. Thanks again to everyone who has participated so far.
2) The simplest design usually seems to be the best one.
3) In this case, the lightest design will probably be best too. These planters are almost as light as they come. The main weight is the compost.
4) We should do as much of everything on the ground as possible and haul it up rather than do it on roofs, like staining the wood and mixing the potting mix.

5) I think the big successes of this initial design were developing a way to avoid using too much plastic and keep the planter weight down, starting to conceiving a way to have rain fill the reservoir, and just generally beginning the design and building process.  There were some failures (er, not-yet-successes) too:

1) I couldn’t really figure out a way to suspend the mix high enough above the pond liner so it doesn’t weigh down and touch the bottom.

I tried and failed to come up with a way to clamp the fabric to the inside of the planter about 7″ down so we’d get a reliable 7″ hang, but I couldn’t do it. We’ll have to figure something out for mass applications of these things.

2) We’ll see how quickly root rot destroys the plants.  Actually, I didn’t completely plant one of the planters and still may have the opportunity to come up with an aeration solution.  This would give us beta version 1.1.  I plan to plant spinach and broccoli in the fall so the goal is to figure out a solution before that.
3) I didn’t work out all the costs yet but I kept the receipts. We can minimize costs by working with compost projects and growing from seed rather than buying and buying. Pond liner costs about 65 cents a square foot.
4) I didn’t weigh everything, but we should be able to do some tests and figure that out too. The finished planters are heavy.

Is there anything else? Not quite yet. The next step is to experiment with installing planters on boards that span rowhouse roofs, putting the weight on the party walls. There will be photos galore from that experiment, so stay tuned.

Welcome to the Philadelphia Rooftop Farm’s first foray into blogging.

The Philadelphia Rooftop Farm (PRooF)


Philadelphians are not alone in facing substantial barriers to accessing healthy, inexpensive food in their neighborhoods — especially local, organic produce.  There is a lack of quality supermarkets throughout the city, and communities that host regular farmers’ markets are still few and far between.  Like many other urban dwellers, Philadelphians live far from farmland and often feel disconnected from even the most basic links in the food chain.  Because we feel distant from sustainable, healthy produce, Philadelphians too often eat overly processed food that is unhealthy both personally and environmentally.


Philadelphia is in a unique position to face these challenges because of one of its most distinctive architectural features: over an estimated 300,000 to 400,000 single-family houses, apartment buildings and commercial building have flat roofs.

Some view these roofs as a black-topped, heat-soaking detriment.  Local urban farmers and green builders from the Philadelphia Rooftop Farm (PRooF) disagree.

PRooF conceives Philadelphia’s 400,000 flat roofs as a potentially empowering untapped resource that can be used in a thoughtful and efficient fashion to better the City environmentally, nutritionally and economically.  PRooF sees these rooftops as one keystone of Philadelphia’s future as a green and healthy city.


PRooF intends to create an unparalleled not-for-profit urban farm that will take advantage of the city’s substantial flat roof acreage to make fresh, nutritional, inexpensive and extremely local food available to Philadelphians.  PRooF will work with owners of individual houses, apartment buildings and commercial buildings, as well as with neighborhood organizations, to build and maintain high-yield organic vegetable and fruit gardens on flat roofs throughout the city.  PRooF will harvest and distribute food from these roofs, sustaining itself by selling farm-fresh fruit and vegetables at farmers’ markets, at neighborhood farm stands and through a CSA (community-supported agriculture), sharing its bounty with its farm hosts and neighborhood organizations.

PRooF will also work with organizations throughout the city that focus on sustainability to pursue an integrated vision of what a city has to do be healthy and green.  Specifically, PRooF will help fulfill many targets of the Greenworks Philadelphia plan recently put forth by the Mayor’s Office of Sustainability.  Growing fruit and vegetables on rooftops will help the city by lowering energy consumption (greening a roof helps cool down the building below it), increasing greenery that cleans the air, minimizing landfill waste by promoting composting, providing food equity to the local neighborhoods where these rooftop farms exist, reducing stormwater runoff, and ultimately providing jobs for those involved in building and maintaining the farm.


PRooF is currently laying the groundwork for a pilot project to start a ten-roof distributed farm during the 2010 growing season.  PRooF plans to document every aspect of the endeavor, from cost of planter components to the amount of person-hours each task takes, from poundage of fruit and vegetable yield to the market sale value of the harvest, and use this information as the basis for a more substantial farming venture in 2011.  Recently PRooF volunteers have been engineering sturdy, low-weight, low cost, self-watering planters that we will test throughout the 2009 growing season and install on the pilot program roofs next year.  We are communicating with other rooftop farmers from cities like Portland, Milwaukee and Montreal to share rooftop farming knowledge and experience, and hope to implement many of their ideas this season and next.


Right now, PRooF would just like those within Philadelphia’s sustainability community to know the project is here.  We want to talk with you about PRooF!

While PRooF is very much in the incubation stage, we are confident in Philadelphians’ ability to work together to face economic and environmental challenges, and are excited for the possibility of working with anyone and everyone to transform the city into a modern marvel of urban green.

For more information about PRooF or to suggest people or organizations you think may like to be involved in any way, please contact Jay Sand at or 215-913-2679.