Horticulture is an essential part of Europe’s regional food and economic security. Greenhouse cultivation grants year-round yields even where degraded soils and poor climate limits conventional farming.
Expanding regional fruit and vegetable supply will also gain importance as climate change disrupts global food production. Europe’s food imports come from some climate-vulnerable regions while its own growing regions are coming under pressure from historic droughts.
Yet European horticulture is marked by highly unsustainable practices. The high-tech, high-yield greenhouse cultivation that prevails in northern Europe is very resource intensive compared to field cultivation. Low-tech operations that dominate in southern Europe exhibit low levels of recycling and circularity, an issue when basic resources like water and productive land are being hit by climate change.
Europe’s fruit and vegetable production needs a sustainability overhaul, from its soil inputs to the building materials used in greenhouse construction and outdoor plot protection. This is where biobased and circular methods can help us produce more with less.
The problem with soil
One of the most difficult and unsolved problems in sustainable horticulture is the material used for growth media – whatever substance is used to anchor plant roots as they grow.
Achieving sustainable horticulture hinges on developing new kinds of low-impact growth media. Soil, especially peat, is still dominant among producers but the latter is particularly harmful which is removed straight from endangered and fragile ecosystems.
Increasingly, food producers are turning to soilless media like rock wool as more sustainable alternative. Rock wool is an inorganic material that gets rid of the need for soil but is non-renewable. Other options are organic substrates like bark.
However, renewable materials like wood still fall down on performance and more work is needed to get effective substrates on the market.
Organic materials are less able to retain water than peat. They also suffer from unbalanced salinity and pH. Wood fibres are also known for nitrogen immobilisation, which makes it difficult for the plants to take up this key nutrient. Finally, all growth media in use today are extremely difficult to recycle even though they contain lots of nutrients and structural matter that could be used again.
The company ICL Group has created its wood-fibre Fibagro Advance growth media that it says overcome the challenges producers face when using soil alternatives. However, their product is not circular as it is manufactured from forestry wood rather than sidestreams.
Growing alternatives
The EU’s Horti Bluec project tried to address the dearth of circular and sustainable horticultural media by experimenting with waste sidestreams. It aimed to devise growing mediums made of waste that are abundant across many regions, something that would make it cheaper for producers to access them.
One of the potential feedstocks they investigated was shellfish waste, which contains the wonder-material chitin. The material can increase the nutrient-retaining capacity of other materials that make up the growth media.
Two other wastes – media that has already been used to grow plants as well as plant waste – can become feedstock for biochar, a burnt residue made of carbon and ashes. Biochar’s capacity to trap carbon has drawn attention as a bio-based carbon capture tool that could allow food production contribute towards emissions targets.
Horti BlueC also explored using plant fibres that could act as a nutrient and water-retaining filler for various soilless horticulture media.
These are all viable waste-based options. Yet the commercialisation of fully recycled used growth media is still a long way off. Experts think that after water, nutrients and fertilisers should be the top priorities for recycling in the food system but it presents one of the hardest technical problems that stands in the way of sustainable horticulture.
Given the constraints on circular soilless growth media, some say hydroponic indoor farming could be the answer. Under hydroponic cultivation, plants are grown suspended in circulating water rather than pots of soil or solid matter. This cultivation method can also cut fertiliser and water usage and prevent chemicals from leaching into the environment.
However, hydroponic growing does not cut the need for solid matter altogether as plants will often still need some substrate for the roots to grab onto even as the water circulates around them.
An EU Horizon 2020 project developed Mosswool designed to replace non-renewable stone wool as well as peat in hydroponic systems. The material uses sphagnum moss, a plant feedstock that is much more sustainable than peat as they regrow after harvesting relatively quickly. The project has developed a patented way of harvesting the species wild in a way that encourages rapid regrowth.
MossWool has already been subject to non-commercial testing in controlled and commercial scale greenhouses. A manufacturing plant is now under construction.
Boxes and pesticides from tomato waste
Tomatoes are the most popular fresh horticultural project in almost all European countries leading to great interest in using bio waste from the crop for new purposes.
An interesting biotechnology awaiting commercial investment are biopesticides from tomatoes, which are among the most popular fresh horticultural products in Europe.
The plant contains bioactive phytochemicals that are less toxic than synthetic pesticides and are safely biodegradable. One study published in 2021 showed that biochemicals from tomato crop vine residues could be used to control insect populations on tomato, cucumber, and pepper crops.
A lower tech use for tomato waste has been found by Dutch company The Greenery has been using cardboard boxes made from the leaves and stems of tomato organic waste added to recycled paper.
Insects give plants a boost
Horticulture need not be just a waste consumer – it can also occupy the midway point in a full circular system. The industry generates large amounts of its own byproduct, often nutrient-rich organic matter that offer the raw materials of greening other industries, including adjacent ones like fertiliser.
Indeed, horticulture’s current dependence on fossil-based fertiliser is a huge problem. Once in the soil, it leaches into water and rivers. Already, humanity has breached safe ecological limits for phosphorus and nitrogen in the environment and must find new ways of producing healthy crops as a matter of urgency.
Horticulture itself might hold the seeds of a solution. Alicante-based Bioflytech is taking nutrient-rich organic wastes from food producers to feed their farmed insect larvae. The organisms function as ‘biofactories’, capable of naturally metabolising low value horticultural wastes into high quality organic fertilisers.
Larvae digest organic wastes into a homogenous, chemically stable farming input that can be used in home gardening or larger-scale agriculture. Using gardening wastes to replace the fossil and synthetic chemicals in modern fertiliser is a highly efficient way to close the loop in food production and reduce the ecological damage wrought by food production.
Depending on the location of production, these [recycling] solutions can be realised by growers and farmers on-site, but the need of high financial investments or high specialisation can lead to off-site solutions that need off-site partnerships and careful transport planning.
Waste to food
Other startups are using horticultural wastes to create new food ingredients and staples. These require less land and carbon-intensive inputs than those from conventional field agriculture.
Italian food-tech company Circular Fiber produces a cooking flour named Karshof made from artichoke side streams. The company claims their product boasts a 50% lower carbon footprint and a 90% lower water footprint compared to regular types of flour made from grains cultivated in open fields. Their product makes use of an abundant low-value waste given that 75% of the weight of harvested artichokes are scraps.
Netherlands-based Grassa passes grass and other horticultural side streams through their refinery techniques to extract functional proteins, minerals and more digestible fibres for animal feed. Their demo plant in Afferden, The Netherlands, can process 3 tonnes of feedstock per hour.
Grassa aims to tackle European livestock’s dependence on soy feed from massive South American plantations that destroy prime natural habitats. As their product are refined from waste closer to home, it holds a much smaller environmental footprint.
Favourable winds for sustainable horticulture
Europe cannot resort to prevailing pathways to horticultural productivity. Modern fertilisers are eroding our soils, contributing to pollution, and damaging biodiversity. Since greenhouse cultivation depends on healthy environmental processes in the final instance, production that disrupts nature’s carrying capacity will only undermine food security in the long term.
A circular horticultural sector could go someway to slowing the destructive impact of our food production on the environment. This was recognised by Europe’s Green Deal strategy which placed sustainable horticulture as a pathway to decreasing net emissions from agriculture.
However, conscious efforts are needed to redesign horticulture along sustainable principles. Greenhouse cultivation is often held up as a panacea for environmental ills of arable and livestock farming but can themselves contribute significant greenhouse emissions through lighting, heating, and fertilisers.
More must be done to either encourage price premiums for the products of sustainable practices or to subsidise growers adopting them. This, coupled with a lack of knowledge among producers, are major barriers to mainstreaming circular practices.
Some regulatory stimulus from the EU could encourage producers to adopt new methods. Already under the Common Agricultural Policy, producer organisations can collectively apply for funding to support sustainable practices. The Farm to Fork initiative also sets out initiatives to make the food system more environmentally friendly by 2050, with targets such as the reduction of nutrient losses and fertiliser use by at least 50% and 20% by 2030.
