Hydroponic and aeroponic growing has received a lot of attention in recent years as the future of farming, since it’s been linked with the associated concept of vertical farming. Vertical farming is having something of a moment, with the tech industry pouring money into it and arguing that it’s the answer to feeding the urban masses fresh, local food, as we roll further into a century facing huge population growth.

What is vertical farming?

The concept of vertical farming is the brainchild of Columbia University Professor Dickson Despommier, who developed it in discussion with students he was teaching as part of a course on Medical Ecology. The idea behind it was to grow food ‘vertically’ in disused urban spaces, using a hydroponic or aeroponic (where plant roots are misted rather than submerged) system. Despommier argued that foregoing soil offered a way of mitigating widespread soil degradation, and that vertical farming could provide a local food source within cities, where the space to grow food in soil, on a significant scale, is minimal.

Supporters of vertical farming argue for its sustainability – but this necessitates leaving a belief in the importance of soil behind. At its best, it is a ‘closed loop’ system, that recycles inputs; and its efficiency in minimising water is an important part of why proponents feel vertical farming is sustainable. It has much to offer urbanites in the production of fresh food throughout the year. Aerofarms, one of the largest vertical farming businesses, is a global company, producing food across four continents, but their focus in on growing food for a local market. Their growing cloth medium is reusable and made from BPA-free, post-consumer recycled plastic.

Hydroponics and organic food

There is fierce debate, however, over vertical farming and the hydroponic and aeroponic production systems it overwhelmingly depends on, and it’s an argument that reaches into the heart of how we define ‘sustainability’. Hydroponic growing has been in commercial use since the early 20th century. Plants are grown in water or in an inorganic fabricated substrate, in buildings that may or may not have windows – if not, LED-lighting is used. The biggest criticism it faces is that plants are fed with artificial nutrients, because they don’t have access to the microbiology of healthy soil.

This goes against one of the most fundamental early articulations of organic farming principles from Lady Eve Balfour, the leading founder of the UK’s Soil Association, that, “the health of soil, plant, animal and Man is one and indivisible.” For that reason, the UK’s Soil Association has refused to give organic certification to produce not grown in soil, and critics see it as ‘wet’ chemical farming, where chemicals are simply added to water instead of the soil.

However, proponents argue that, because conditions can be completely controlled in the sterile environment the plants are grown in, there is no need for pesticides and vertical farms can produce higher yields on much less ground. This is an argument for efficiency and control that was widely used to support the factory farming of livestock; but it is now apparent that many diseases spread even more rapidly in these indoor situations than in free-range systems. So might the same eventually be the case with vertical farming? The question also arises whether a sterile environment produces sterile food – and if it it does, what will be the long term impact of that on the gut microbiome and on our immune systems which depend on it? There is much debate on the nutritional value of hydroponic plant production, but the jury is still out on that front.

The SFT’s chief executive and former Soil Association director Patrick Holden has long-standing doubts about the sustainability of hydroponic systems. As an organic farmer, he depends on the fertility of his soil to produce wholesome food to feed his herd of Ayrshire cows whose milk is turned into Hafod Cheddar, an award-winning cheese. He also sees the symbiosis between ruminants and the land as critically important in building and maintaining soil organic matter so that it can absorb water and mitigate the damaging impact of both heavy rain and drought. By locking up carbon in organic matter, healthy soils also avoid the need for chemical fertilisers and help to reduce global warming.

Patrick also believes that the widespread advocacy of hydroponics is misplaced. He says, “Feeding plants through chemical nutrients in solution is analogous to feeding a human patient in hospital by intravenous solution. That is valuable in treating serious ill-health in humans, but in relation to food production, it excludes the vital role of soil as ‘the stomach’ of the plant in breaking down organic matter and completing nutrient cycles, on which many planetary ecosystems ultimately depend.”

The issue of the organic certification of hydroponic production threatens to become a potiical hot potato in the UK because of Brexit. The National Organic Standards Board, a committee which advises the United States Department of Agriculture has voted narrowly to allow crops grown hydroponically and aeroponically to carry an organic label in the US. This has upset traditional organic producers. Dave Chapman, an organic tomato grower in Vermont has been quoted as calling it a ‘tragic failure’.

The question which arises, therefore, is whether such produce will also be on sale as organic in the UK if a trade deal with the US is concluded, as those pro-Brexit hope and expect?

The spectrum of sustainability

On a smaller scale, companies like Grow Bristol, whose tagline is ‘Fresh. Local. Sustainable.’ provide one example of the social and agricultural role that vertical farming with hydroponics can play in an urban city centre. Dermot O’Regan, who runs Grow Bristol, has a background in environmental policy. He was interested in providing food year-round to the local community in Bristol. O’Regan was concerned by the heavy water use in agriculture, and, since there wasn’t much soil in downtown Bristol anyway, it made logical sense to buy a shipping container and start a hydroponic farming enterprise inside it.

Grow Bristol is set-up as a Community Interest Company with a social mission, and education and engagement is a component of what they do, inviting groups in to visit and offering training opportunities for volunteers and eventually, possibly, jobs to the local community. At the moment they grow micro-greens for a range of restaurants and shops through the city. Like many committed to vertical farming, they see Grow Bristol as a component of the wider food system, one aligned with sustainability, rather than with the environmental degradation of industrial farming.

Grow Bristol has also explored a related system – aquaponics – which arguably remedies the issue with artificial nutrient solutions that the industry is dependent on. In an aquaponic system, fish waste provides the nutrients for the plants that are grown – often in soil. Aquaponics is a long-standing practice in Asia, reaching back centuries, and it incorporates microbiology in the system. The production system has been expanding in the US in recent years, however, its tenuous financial viability – Grow Bristol dismantled its aquaponic system after a nine month trial – remains an issue. 

Vertical farming’s viability

Vertical farming has also struggled with financial viability and this has consequently limited what can be grown this way. The cost of energy can be significant, and some crops are much more expensive than others. Consequently, this system has been primarily used for the production of greens such as kale and spinach, and micro-salads. The energy that goes into producing more substantial vegetables like potatoes and other root vegetables makes these crops prohibitively expensive. Stan Cox of the Land Institute has pointed out in an interview that, “if you got a plant like tomato or sweet corn…that produces a fleshy product, that requires about 1200 kilowatt hours of electricity for lighting to produce one kilogram of food minus the water that’s in the food. That’s about the annual energy consumption of the average American refrigerator for a year, all to produce just two and a quarter pounds of dry matter.” So, in recent years, the narrative around this production method has focused more and more on its role as a part of the wider food system, rather than as a replacement for it.

It is this issue of cost that raises the thorniest question around vertical farming and hydroponic production – if financial viability lies only in the production of high-end micro-salads, lettuce and greens, how much of a part in the wider food system can it really play? The question is a significant one, particularly as more and more wealth is being centralised in cities with gentrification now one of the most prevalent forms of urban development across the globe. Vertical farming based on hydroponic production may be serving a niche market with a niche price, for Silicon Valley entreprenuers in the tech industry looking for the next cool food, but whether it is a genuinely sustainable way to provide staple affordable foods for the population as a whole, is clearly debatable.