If you announce that you're thinking of growing grass indoors, you're likely to get a bunch of new best friends, along with some interest from the cops.

But for some researchers, indoor farming is taking on a whole new meaning. They're hoping to do lots of it, right in the centre of the city.

Traditionally, farming has been a horizontal affair; you do it on the ground, in fields or vast greenhouses. Researchers like Gene Giacomelli, director of the interdisciplinary education, research and outreach programme for greenhouse and other advanced technology systems at the University of Arizona, are hoping to see a move to vertical farming, where you grow plants in tall buildings.

"You could put multiple layers of hectares of food production in a vertical system," he says. "The benefits are that you would bring food to the people. Transportation costs and time to get to market are minimised, and you have the potential to use your resources more effectively, meaning that you can take the waste resources from a food production system and use them with a building system and vice versa."

Dickson Despommier, professor of public health in environmental sciences at Columbia University's Mailman School of Public Health, has been working on the Vertical Farm Project with his students for years. He argues that traditional farming is challenged as land constraints and transportation costs make it less efficient. Farming food closer to our cities rather than growing food far away is a smart move, he says - if we can find the political and economic muscle to make it happen.

Vertical farming is an interdisciplinary field, encompassing everything from nutrition to urban design and public health. A quick look at Despommier's web site reveals some exciting design concepts. No wonder that it is in vogue among architecture students, who have to grapple with challenges such as getting enough light into buildings, and handling water flow.

Toronto's Gordon Graff is still working on his Skyfarm masters project - a proposal for a building designed for a particular Toronto block. His design features a sloping building with plant facilities on the outer side, next to the windows. Solar panels also help to offset energy usage, and he even plans a methane digestion plant to help fuel the building.

"It would grow grass with a high methane content [and] the harvested growing material is [then] fed into a methane digester," he explains, adding that the digester would also take sewage from the city system to help generate power.

Graff thinks that such vertical farms are more likely to be useful for residential rather than for commercial buildings. "A company's HQ is not the right market," he says. "Vertical farming as a profit generator cannot compete with rental prices per square foot in downtown Toronto." Conversely, residential deployments would put the food close to where people need it, he says.

However, Despommier is sceptical that agricultural space can be added to operational residential or commercial properties. "You would not retrofit residential or commercial buildings because you cannot protect your food," he argues. "You have to keep the plants away from infectious diseases by growing them inside positive pressure buildings."

Despommier also dismisses methane digesters as a means of generating power, arguing that they are 90 per cent inefficient. Better instead to separate liquids from solids, dry them with a centrifuge and incinerate them, he says. " If you just burned it it's about 60 per cent inefficient. I would get 60 per cent of the energy content back."
However, he is not against certain existing buildings being converted into indoor farms, arguing that retrofitting abandoned warehouses and apartments to grow plants is entirely feasible and could generate a healthy profit. And with its property market heading quickly for the gutter, the shells of former US businesses could be depressingly easy to come by.

You want to make money? Convert a five-story warehouse into a vertical farm, grow sugar beets, extract the ethanol, and sell the fuel, Despommier advises. Or set up in Dubai, and use a vertical farm to cleanse grey water and turn it into drinking water. That may sound implausible to some, but researchers are talking about hydroponic crop densities tens of times greater than you would find in traditional fields. Dubai has a shortage of fresh drinking water, and it's the same in Israel, where he says buildings are already integrating plants into their infrastructure for grey water reclamation.

The concept of water recycling is an area both Graff and Despommier agree on. Graff advocates the "living machine" concept originally developed by John Todd, in which artificial wetlands are engineered to purify natural resources such as water.

Other ideas that could find a home in vertical farms include the production of high-value plants, such as those that produce the basis for anti-malaria drugs. Genetically engineering such plants to produce more of that material could make them particularly suitable for high-density vertical farming, suggests Despommier.

"Find investors with a cash value of $30-$50m," he advises. "You invest $50m, and rope in a university with an agricultural school to help you. You give them a grant for this, and in three years, you can work out all of the kinks of energy delivery, water recovery, harvesting, planting, dealing with plant diseases. Then you will have a prototype telling you how big the scale-up would be. That is happening as we speak, I can almost guarantee you."

Giacomelli also sees some potential for selling locally-grown food. "You will not find staples but you could find speciality products, such as high-quality tomatoes, peppers, and fresh herbs," he says. "People would pay more for those because they’re fresh cut and locally grown. You could succeed with a good marketer, and a good business plan that would include food production as part of a building's purposes. It wouldn’t be the building’s sole purpose, but yes, it could fit into the bigger picture for producing fresh food. "

Restauranteurs or food retailers with deep pockets and a long-term outlook could find that concept appealing, but given all the potential benefits why hasn't this happened in the US already? Despommier says that the country is caught up in a state of inertia, failing to take action until constrained resources force the business community to address a problem. If true, then the rising cost of food and concerns over the arable land being given over to ethanol production should spark interest in the idea. In practice, the tightening of credit conditions following the collapse of the financial markets could put a spanner in the works. Even abandoned warehouses cost millions to renovate.

Despommier would like to see the Government kick in some of the cash. "Can horizontal farming make money? Of course not! Farming is subsidised. But how are you going to do without food? So if it is an essential for the stability of the country, then someone has to pay for this,” he observes, adding that just a billion dollars from the monumental $288bn Farm Bill would go a long way towards kickstarting the concept.

While we wait for entrepreneurs to turn abandoned industrial parks into urban farms, we'll have to content ourselves with paying a little extra at the checkout counter. Hopefully, if forward-looking people can see potential in the idea, we will get some smart money, not to mention some delicious tomatoes, moving in at the ground floor.