Some meandering thoughts about rooftop gardens..

[Ian James Gordon]

I expect since you are reading this you've probably heard the how many things a tree does spiel over and over. They're marvellous things trees in that they create habitat for everything from microbes to woodpeckers, they filter water, store water, breathe water, seed rainclouds, clean air, inhale carbon dioxide and exhale oxygen, store carbon, modify climates, hold soil, build soil etc etc etc

Doubtless you've also heard this or that architect say how they would like to design buildings that enrich the environment in the multiplicity of ways that trees do. While that's all well and good it does seem like something that's going to be coming tomorrow for at least twenty years.

I don't think it needs to be that way. I believe that existing buildings can be retrofitted so that they provide some of the things we get from trees, and I believe that starts with roof gardens.

Doubtless you've seen this or that space age thing on top of a building in Tokyo. Whether it's rice in Roppongi or Sweet Potatoes grown hydropomically on an NTT roof I'd have to say it's not there yet at all. Anytime you put an expensive high tech and 'high input required' system in place and then grow annual crops on it so that manpower requirements remain high in perpetuity you have to wonder how long it will last. To me the NTT thing is a stunt and growing rice in the middle of Tokyo is a bit of a joke. It's fine as a starting point to educate but not much use beyond that. Mostly likely you've seen a square of anaemic sickly grass on a square on the roof. I figure the hanging gardens of Babylon did a better job.

Growing plants on a roof means lots of exposure to the sun, plants tend to dry out and need lots of watering. The problem with this is when you water a plant pot from above you wash the nutrients downwards out of the soil. You'd want to water liberally or you'd have to spend your entire day up there. Now however there are plant pots with water reservoirs in the bottom of the pot. The plant is encouraged to push its root system down to get at the water and because the water flow is upwards the nutrients don't leech out of the soil. Maintaining a water reservoir at the bottom of the pot is an engineering challenge on the level of fixing a toilet. You could leave your roof garden for weeks at a time, knowing that the next rainy day will replenish your water barrel from the buildings guttering.

Growing food in hydroponics would I imagine not allow the plants to generate all the bio associations it would in healthy soil. It would also limit the kinds of plants you grew to a monoculture as well I'd think, since different plants have different chemical tolerances and food is coming in a liquid form. I believe it's an example of man paying to do what nature would do for free if you gave it a chance. The first is unsustainable, the second is not.

When you put plants in soil, you could add biochar, you could sprinkle beneficial fungi spores on the roots if you wanted to fork out money for such things. On the other hand you could take a rice box into the forest bury it for a week and then bring it back and add it to your soil. There's a huge difference between the productivity of pasteurized potting mixture and soil teeming with beneficial, resilient micro-organisms. The inputs that the Korean natural farming system teaches farmers to make for themselves is no more complicated than making kimchi and the results are spectacular.

If you are using soil in diverse interconnected pots with a common water supply you can create a polyculture, with sun loving plants providing shade to plants which wilt down to nothing in full sunlight. If those plants are perennials, as the Permaculture system recommends, organized into plant synergies or guilds, then the vast majority of the labor requirements are in the design stage. Sustainability in this sense would be the benefit of getting produce from the garden year after year with little to no input from the gardener. A lot of people would be up for that I think.

Now I will leave you to consider the numerous ways in which citizens, businesses, local goverment, national government would benefit from a Tokyo wide network of rooftop gardens. I imagine you'll come up with twenty ways at least. Now imagine the possible number of beneficial interconnections between these stakeholders and I imagine that even with bullet points you'd be talking about twenty to thirty pages.

This is what you would get from a toilet system, networking and some knowledge about how to combine diverse gardening systems to get the desired level of input and optimal output associated with that.