What is vertical farming and why do we need it?
Let’s start with the why: increasing food demand, a growing population (predicted to reach 9 billion by 2050), climate change and a shortage of arable land are all key factors presenting a serious challenge to food security and, ultimately, to human life.
Vertical farming offers an opportunity to change the way we grow and consume. Current agricultural practices cannot deliver the necessary increases in yield to sustainably feed our population. Vertical farming has been heralded as the ‘future of agriculture’ because of the high level of monitoring and increased efficiency, which is expected to bring both innovation and improvement to farming.
Vertical farming is a popular term used for CEA (Controlled Environment Agriculture) and refers to the practice of producing food on vertically inclined surfaces and in vertically stacked layers. It aims to provide crop protection and maintain optimal growing conditions in an environment that controls light, CO₂, temperature, humidity, air circulation/exchange, water, pH levels, and nutrients. Vertical farms can be integrated into existing structures such as office buildings, repurposed warehouses or even underground unused spaces and can also be purpose-built facilities in, for example, shipping containers.
Leading-edge CEA technology is explicitly designed to maximise yield in a limited space while increasing energy efficiency and reducing the impact on the environment. Here we break down the core tech that makes up a vertical farm.
Growing systems
Vertical farming can involve a range of hydroponic systems, which usually dispense with the need for soil and either remove all growing media (aeroponics) or use alternative substrates (detailed below under “Growing Media”).
Ebb and Flood System
The ebb and flood system, also referred to as flood and drain, works exactly as the name suggests; trays are flooded with a nutrient solution for several minutes before the water subsequently ebbs away, with the roots of the plants bathed in and out of the nutrient solution. Mimicking flood-like conditions encourages the plants to take up oxygen and nutrients, resulting in strong, healthy plants. The ebb and flood system is popular for the production of microgreens.
Nutrient Film Technique (NFT)
The NFT system consists of narrow channels, or troughs, where a continuous small volume of water and nutrient solution flows at the bottom of the channels, creating a thin film. Plants are suspended over the channel usually in net pots, and receive a small volume of nutrient solution several times daily. The thin film of nutrient solution allows the bottom of the roots to be watered but not soaked, while the tops of the roots remain dry and take up oxygen. The NFT culture system is well suited for baby leaves, salads and greens, herbs and strawberries.
Deep Water Culture (DWC)
DWC, as the name suggests, consists of deep troughs filled with a large volume of water and nutrients in solution that is kept mixed and aerated by the continual addition and removal of water at a relatively high speed/pressure, with further oxygenation provided by the bubbling of air through air stones. This ensures enough oxygen dissolves in the water for uptake by the plants. Plants are set in net pots on floating rafts, usually polystyrene. This culture system is well suited for baby leaves and full head salads.
Drip Irrigation
Drip irrigation is usually implemented in covered agriculture (polytunnels, glasshouses) to provide targeted watering to larger plant crops (tomatoes, peppers etc), delivering the nutrients directly over the roots. In vertical farming, drip-fed irrigation is mostly in place in systems which have crops arranged in vertical troughs or towers. These systems are suitable for greens, salads and herbs (such as basil and coriander).
Aeroponics
In aeroponics, the plants grow with their roots hanging in a nutrient-rich mist. Exposed to oxygen, roots thrive in this environment, with nutrients targeted to the plants directly. Aeroponics systems are extremely water efficient, but are more complex to set up and control and minor failures in the system of nutrient mist delivery can be catastrophic for the crop.
Growing media
There are several types of growth media that are used in vertical farming; the most commonly used are rockwool, coco coir, compost, jute and carpet remnants. Each has its own merits and disadvantages.
Rockwool
Rockwool is a media formed from mineral rock (basalt) that is heated until molten and spun into fibres. It is excellent for providing adequate aeration to plant roots, while maintaining enough water to keep the plants moist but not soaking. Unfortunately, despite being made from an organic substance, rockwool takes many years (if at all) to break down in the environment. Rockwool can be used to grow successive generations of plants, however it requires sterilisation between growth cycles, which can be problematic if rapid turnover of plant material is required.
Coco Coir
This media is made from the natural cellulose fibres of coconut husks. It is mostly used in a disc or mat form. Similarly to rockwool, it is good at aerating plant roots and maintaining moisture levels. Coco coir is biodegradable and agro-renewable, which is appropriate for the sustainable and environmental harm reduction goals of vertical farming.
Jute
Jute is derived from the Corchorus species of plant. The fibres of this plant are spun to form mats that can be used in a CEA set up. Its properties are rather similar to that of coco coir, while also sharing the benefits of being from a renewable source as well as degrading quickly and easily in the environment.
Hemp
Hemp fibre fabric shares many of the properties and advantages of jute.
Compost
Compost is used in many vertical farms, however it is rapidly falling out of favour due to many of the other materials being more environmentally friendly and coming in at a similar or lower price point. As most compost mixes contain peat, there is a large carbon footprint generated in the production of commercial compost mixes. It also needs to be sterilised to remove soil pathogens before use. There is the risk of soil clogging up filters within CEA, so many vertical farmers prefer to use a completely soil free system. The use of compost or compost-containing mixes does not allow for a tight control over nutrient delivery in a VF setting.
Carpet Remnants/recycled
Some vertical farmers use carpet remnants, particularly those with a high wool content, to grow their plants in. Wool fibres help to maintain moisture and aeration while the mat format is great for growing microgreens on. Although not truly environmentally friendly (most carpets contain synthetic fibres that will not biodegrade), it has been suggested that using the remnants for CEA gives a second use to a material that would otherwise go straight to landfill.
Other matting
Specially designed substrates are available for CEA and VF; most notably foam pads with individual wells for seeds, with each seedling developing and the individual plantlets which can be detached for transplanting over the course of the crop development.
Lighting systems
Traditionally, covered agriculture has used high pressure sodium (HPS) lamps. These produce a warm light, typically seen as a yellow orange glow, over areas with lots of glasshouses. As LED technologies have become cheaper and more energy efficient, LED lighting dominates next generation CEA. Whilst HPS lamps produce a yellow-orangey light, LEDs can be engineered to produce any light colour or combination, allowing for the development of LED lighting products designed specifically for the CEA sector and the opportunity to develop and deliver ‘light recipes’ specific to crop types to further photosynthesis, maximise yield and ensure crop quality. In an indoor growing environment, with no external or natural light source, the quantity and quality of the artificial lighting provided to the plants/crops is incredibly important.
Nutrients
CEA provides growers with the ability to control the levels, the frequency and the type of nutrients that are delivered to the crops. Commercially available nutrient mixes are easy and ready to use. However, similarly to light recipes, there is an opportunity to maximise your yield and crop quality by tailoring your nutrient mix for specific crops. Knowledge and research is key to successful nutrient recipes.
HVAC (Heating, Ventilation and Air Conditioning)
Control over the HVAC is essential in the management of a vertical farm as it has the potential to hugely impact on the health, yield and quality of your crops. Smart control systems are increasingly important in the maintenance and management of temperature, ventilation and humidity. It is, therefore, essential to install HVAC systems that have the capacity to be smart enabled and integrated into an overall control system.
Control systems
Control systems monitor and manage all aspects of the controlled environment so that the grower is enabled to make informed decisions for optimal growing conditions specific to crops. Next generation control systems are providing growers with critical data on both the environment and the crop development and health in order to optimise all aspects of the growing environment from light and nutrient recipes to heating and ventilation levels. In addition, control systems allow for the easy management of light intensity, implementation of light and nutrient recipes that may change over the course of crop growth and the delivery of supplementary CO2. Next generation vertical farms must be equipped with these integrated control systems, along with inline monitoring of the crops for disease management, in order to optimise conditions, increase energy efficiency and maximise yield.
This article is an introduction to the essential components of a vertical farm. In our next piece, we will share some top tips on how to choose the lights for your system…