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The Journal of Horticultural Science and Biotechnology
ISSN: 1462-0316 (Print) 2380-4084 (Online) Journal homepage: https://www.tandfonline.com/loi/thsb20
Vertical farming: a summary of approaches to
growing skywards
Andrew M. Beacham, Laura H. Vickers & James M. Monaghan
To cite this article: Andrew M. Beacham, Laura H. Vickers & James M. Monaghan (2019) Vertical
farming: a summary of approaches to growing skywards, The Journal of Horticultural Science and
Biotechnology, 94:3, 277-283, DOI: 10.1080/14620316.2019.1574214
To link to this article: https://doi.org/10.1080/14620316.2019.1574214
Published online: 14 Feb 2019.
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CENTENARY REVIEW
Vertical farming: a summary of approaches to growing skywards
Andrew M. Beacham, Laura H. Vickers and James M. Monaghan
Fresh Produce Research Centre, Crop and Environment Sciences Department, Harper Adams University, Edgmond, Shropshire, UK
ABSTRACT
Pressure on agricultural land from a rising global population is necessitating the maximisation
of food production per unit area of cultivation. Attention is increasingly turning to Vertical
Farming (VF) approaches in an attempt to provide a greater crop yield per square meter of
land. However, this term has been used to cover a broad range of approaches, from personal-
or community-scale vegetable and herb growing to vast skyscrapers for commercial produc-
tion of a wide range of crops. This article summarises the main categories of VF in order to
help clarify this emerging but sometimes confusing area of agriculture and discusses how
scientific investigation of the potential of VF is currently lacking and will be required to help
determine its feasibility as a method to assist meaningfully in global food production.
ARTICLE HISTORY
Accepted 18 January 2019
KEYWORDS
Vertical farming; hydroponic;
glasshouse; controlled
environment; protected
horticulture
Introduction
Agricultural production is experiencing increased pres-
sure to generate larger yields as the global population
rises and demand for food increases. By 2050, the global
population is predicted to reach 9.7 billion, with 70% of
people living in urban environments (United Nations,
2015). In addition, agricultural land may be lost through
the expansion of urban areas and infrastructure develop-
ment (Lotze-Campen et al., 2008), potentially leading to
shortages of farmland (Corvalan, Hales, & McMichael,
2005; Healy & Rosenberg, 2013;Thomaieretal.,2015).
This scale of change may necessitate the investigation of
novel food production methods as both the amount of
and yield achievable from conventional farming of agri-
cultural land is limited.
With the aim of increasing crop yield per unit area of
land, the concept of Vertical Farming (VF) is currently
gathering momentum (Agrilyst, 2017). By farming
upwards rather than outwards, this technique aims to
reduce pressure on traditional agricultural land and, by
incorporating soil-free growing systems, is particularly
attractive for use in urban areas. However, the term
‘Vertical Farming’hascometohaveawiderangeof
definitions that can provide confusion. Often, although
not necessarily associated with urban agriculture, VF
encompasses a range of growth systems of different
scales, users, technologies, locations and purposes. It is
particularly suited to the cultivation of horticultural crops
such as leafy vegetables (Agrilyst, 2017). Here we try to
provide a summary of some the main approaches to VF
and highlight the characteristics of different VF growth
systems.
Categories of vertical farming systems
Vertical Farming systems can be broadly divided into
two categories –those comprising multiple levels of
traditional horizontal growing platforms, and those
where the crop is grown on a vertical surface. Rooftop
glasshouses with conventional, single-level production,
while belonging to the category of urban agriculture
and having the potential for efficiency improvement
through integration into e.g. urban heating and waste
infrastructure, termed Building Integrated Agriculture
(Caplow, 2009; Eigenbrod & Gruda, 2015), are not
considered here due to their similarities to conventional
rural protected horticulture facilities.
Stacked horizontal systems
This form of Vertical Farming (Figure 1(a, b))frequently
adapts existing commercial protected horticulture sys-
tems. Such systems comprise multiple levels of traditional
horizontal growing platforms. Many horticultural crops,
such as leafy vegetables including lettuce (Lactuca sativa)
and herbs, tomato (Solanum lycopersicum)andpepper
(Capsicum spp.) are grown in large-scale glasshouses
using hydroponic systems (Agrilyst, 2017). These can
include substrate blocks formed of rock-wool or similar
materials which provide a matrix for plant roots and are
drip-fed with a precisely controlled mixture of water and
nutrients. Alternatively, plants can be grown in rafts
which float on the surface of beds of nutrient solution
(deep water culture, DWC) or using a thin layer of
nutrient solution in the rootzone (Nutrient Film
Technique, NFT) (Beacham, Monaghan, Aguiar, &
CONTACT Andrew M. Beacham abeacham@harper-adams.ac.uk Fresh Produce Research Centre, Crop and Environment Sciences Department,
Harper Adams University, Edgmond, Shropshire TF10 8NB, UK
THE JOURNAL OF HORTICULTURAL SCIENCE AND BIOTECHNOLOGY
2019, VOL. 94, NO. 3, 277–283
https://doi.org/10.1080/14620316.2019.1574214
© 2019 The Journal of Horticultural Science & Biotechnology Trust
Eastham, 2017; Monaghan & Beacham, 2017). Such sys-
tems often incorporate recirculation of the nutrient solu-
tion to maintain optimum nutrient composition with
additional sterilisation/sanitation steps to control poten-
tial pathogens. Alternative approaches include aeropo-
nics where the rootzone is misted with nutrient solution,
requiring relatively low volumes of water (Weathers &
Zobel, 1992), and aquaponics (nutrient provision from
waste from a fish farm built into the recirculation system;
Rakocy, Masser, & Losordo, 2006).
These horizontal growing systems have the poten-
tial to be stacked on top of each other within taller
structures to form a vertical farm. This can be achieved
either in glasshouses (Figure 1(a)) or in self-contained
controlled environment (CE) facilities, sometimes
referred to as ‘Plant Factories’(Takatsuji, 2010;
Figure 1(b)). Glasshouses have the benefit of being
able to utilise sunlight for plant growth with supple-
mentary levels of lighting being required during peri-
ods of low light, for example during winter or cloudy
conditions, or for areas of the system distant from the
glasshouse periphery or shaded by higher levels of
planting. CE units, however, being fully enclosed,
require all lighting to be provided, thereby increasing
the energy costs of these systems compared to glass-
houses, although the ability to insulate the CE facility
as the walls are not required to transmit light could
offset the cost of heating a glasshouse structure. In
order to minimise energy consumption, increasingly
efficient light-emitting diode (LED) illumination can
be used, with the spectrum of light output tailored to
the individual needs of particular crops (Bourget, 2008;
Massa, Kim, Wheeler, & Mitchell, 2008). Reduced heat
output from LED lights versus high pressure sodium
lamps (Massa et al., 2008) should allow closer posi-
tioning to the crop, ideal for stacked growth levels in
VF facilities.
The choice of glasshouse or CE will also dictate the
location of the VF system. Glasshouses need to be
situated in locations providing adequate irradiance.
In urban settings, this could comprise a free-standing
structure with a glass or polycarbonate shell, built
from the ground up. However, with the high cost of
land in urban areas (Benke & Tomkins, 2017), a more
cost-effective approach may be to build on top or side
of existing structures and place the glasshouse on the
roof of city buildings or alternatively as a ‘green façade’
(Köhler, 2008). CE facilities carry no such location
restrictions and can be placed anywhere with adequate
space. A number of enterprising companies are using
a range of unusual urban sites for food production
using CE systems, such as Growing Underground,
a company producing micro greens and salad leaves
in an unused London Underground tunnel (Growing
Underground, 2018). In addition, CE systems remove
issues of seasonality by maintaining controlled grow-
ing conditions year-round and can therefore poten-
tially increase yield by allowing additional harvests of
short-period crops during an annual cycle or by pre-
venting the influence of seasonal change.
Heterogeneity of growing conditions between
levels in Stacked Horizontal Conditions Systems
is a potential concern. Gradients of temperature,
light and other factors (Jarvis, 1992)acrossthe
different growing levels may result in unwanted
crop variability. A study of a soilless four tier
strawberry (Fragaria spp.) glasshouse system
found significant differences in a number of
growth parameters between levels, with plants on
the top tier showing higher yield and quality than
those on lower levels, thought to be due to the
greater availability of photosynthetically active
radiation (PAR, Murthy, Karimi, Laxman, &
Sunoj, 2016). In glasshouse-based systems, to
attempt to ensure that each level of the stacked
system receives an equal share of light, supple-
mentary artificial lighting or a rotating mechanism
that moves each level in turn to the top of the
Figure 1. Representation of vertical farming (VF) types. Stacked horizontal systems comprise multiple levels of horizontal
growing surfaces and can be located in glasshouses (a), sometimes with level rotation incorporated, or controlled environment
(CE) facilities (b). A variation of this approach is that of multi-floor towers (c) where each level is isolated from the surrounding
levels. The use of balconies (d) for crop production is another example of VF using stacked horizontal growing surface. Vertical
growing surface include green walls (e), which can be positioned on the side of buildings and other vertical surfaces and
cylindrical growth units (f) with vertical arrangements of plants.
278 A. M. BEACHAM ET AL.
stack can be used to reduce shading of lower levels
and maintain homogeneity of growing conditions
for each level (Massa et al., 2008;Morrow,2008).
Sky Greens, a company based in Singapore, use
a gravity-assisted rotating growing system with
multiple tiers of troughs in an attempt to reduce
supplementary lighting need and overall energy
consumption (Sky Greens, 2018).
Stacked horizontal systems tend to be used in large-
scale commercial enterprises, growing relatively large
volumes of one or several types of crop (for example,
lettuce, spinach (Spinacia oleracea) and tropical leafy
vegetables by Sky Greens (Sky Greens, 2018)). Crop
choice in Stacked Horizontal Systems can be dictated
by the space available between each level, with shorter
crops allowing for a higher number of levels and so
potentially greater yield per unit height of the growth
system. For this reason, smaller crops such as micro-
herbs and spinach (Spinacia oleracea), which also ben-
efit from fast growth, in turn maximising turnover and
profit, are often favoured for their compact growth
habit (Agrilyst, 2017;Table 1). Use of stacked levels
for taller crops such as tomato and pepper may require
changes to cultivation methods and crop varieties to
achieve high yields from shorter plants.
Multi-floor towers
A variation on the concept of Stacked Horizontal
S
ystemsisthatofMulti-FloorTowers(Figure 1(c)).
In this scenario, rather than the multiple levels of
plant growth occurring in the same chamber (glass-
house or CE), the different levels of planting are
locatedondifferentfloorsofatowerstructureand
so are isolated from each other. This allows differ-
ent conditions to be maintained for each level of
planting which can allow a wider range of crops to
be grown by tailoring the conditions of each level
to best suit each crop. By using a physical division
between each level of planting this approach is
most suited to CE systems. However, despite
numerous designs (Mok et al., 2014), no Multi-
FloorTowersystemsarecurrentlyinexistence.
Balconies
An alternative to indoor growth in Multi-Floor
Towers is the use of balconies for growing produce
(Figure 1(d)). This approach is more suited to
production on an individual or community basis
rather than commercial enterprises but may prove
useful for the personal production of low-volume
crops such as herbs.
Vertical growth surfaces
Green walls
Green Walls comprise vertical or inclined growing plat-
forms sited in locations such as the façades of buildings
(Figure 1(e))(Köhler,2008). Potential issues with green
walls include the ease of harvest of plants high above
ground level, exposure to urban pollution in walls not
covered by a protective surface and maintenance of an
equal provision of water from the top to bottom of the
wall. Another consideration for the location and dimen-
sionsofgreenwallsisthatoflightavailability.Arecent
study (Song, Tan, & Tan, 2018)soughttoevaluatethe
availability of PAR along building surfaces in an urban
environment, in this case a high-density residential area
of Singapore. Based on estimates of plant light require-
ments calculated from leaf physiological traits of seven
leafy vegetables, the study found that façade areas
exposed to direct sunlight for a minimum of half
the day provided sufficient PAR for plants with high
light requirements. The amount of available PAR
increased with building height but was also influenced
by façade orientation and configuration, with east-west
orientated buildings considered to be better for contin-
uous cultivation by avoiding the effects of north-south
oscillation of the sun. The study also highlighted a risk of
excessive and perhaps deleterious PAR levels during the
middle of the day in some areas. These findings prove
promising for the cultivation of vegetables in green walls
but will need to be reassessed to determine growing
conditions in temperate cities and different latitudes.
Cylindrical growth units
In this type of system, plants are grown one above
another around the surface of upright cylindrical units
housing a nutrient supply (soil or hydroponic sub-
strate) and located within a glasshouse or CE facility
(Figure 1(f)). A comparison between a Cylindrical
Growth Unit and a conventional horizontal growing
surface has been made using lettuce (Lactuca sativa cv.
‘Little Gem’) (Touliatos, Dodd, & McAinsh, 2016).
Both systems used hydroponic culture and artificial
Table 1. Examples of crops grown in VF systems in commercial enterprises and academic studies.
Crop Source
Micro greens Growing Underground, 2018; VertiCrop, 2018
Salad leaves Growing Underground, 2018; AeroFarms, 2018; VertiCrop, 2018
Strawberry (Fragaria spp.) Murthy et al., 2016; Saturn Bioponics, 2018; VertiCrop, 2018
Lettuce (Lactuca sativa) Sky Greens, 2018; Touliatos et al., 2016; Saturn Bioponics, 2018
Spinach (Spinacia oleracea) Sky Greens, 2018
Tropical leafy vegetables Sky Greens, 2018
Assorted leafy vegetables Song et al., 2018
Culinary herbs Saturn Bioponics, 2018; VertiCrop, 2018
THE JOURNAL OF HORTICULTURAL SCIENCE AND BIOTECHNOLOGY 279
lighting. The study found that although photosynthetic
photon flux density (PPFD) and lettuce shoot fresh
weight decreased significantly from the top to the base
of the cylinder unit, the Cylindrical Growth Unit was
still able to produce more crop per unit floor area than
the horizontal growing surface. Additional artificial
lighting could help to increase crop uniformity in
such systems (Touliatos et al., 2016). Cylindrical
Growth Units have been used to grow lettuce, straw-
berry and a range of herbs (Saturn Bioponics, 2018).
Considerations for vertical farming
One of the major issues currently facing Vertical
Farming is that of a paucity of scientific studies of
the yield potential, crop quality, energy efficiency and
other parameters of VF systems in order for their
potential to be properly assessed (Al-Chalabi, 2015;
Eigenbrod & Gruda, 2015; Mok et al., 2014; Pinstrup-
Andersen, 2018). However, here we summarise some
of the key considerations for VF systems and their
implications on its potential future success.
Crop choice
Crop range in VF systems is currently limited, with most
producers predominantly favouring salad leaves and
other small leafy vegetables (Agrilyst, 2017;Table 1).
These crop types are well suited to cultivation in VF
systems for a number of reasons. Their small size allows
them to be grown in facilities such as stacked horizontal
systems or cylindrical growth units where space, parti-
cularly in the vertical dimension, is at a premium. Small
plant size also allows a higher number of plants, and so
potentially increased income, per unit area horizontally.
These crops also tend to show rapid growth and a short
timeframe from germination to harvest, increasing the
number of crops that can be produced in a season,
further maximising profitability. A rapid turnover of
crops also allows increased flexibility in planting regime
in terms of crop choice and allows growers to better cope
with problems such as crop loss due to disease or pest
damage.
Whilst some small leafy crops such as culinary herbs
and salad greens would be expected to experience rea-
sonably consistent demand year after year, growers of
more ‘trendy’vegetables such as micro greens may need
to be amenable to rapid changes in crop choice if such
crops experience a rapid decline in demand, in order to
be replaced by others. Again, the short production
cycles of such crops will prove helpful in this regard.
Investigation of the suitability of VF for the pro-
duction of other crops may help to expand produce
range and income, with some growers already using
VF for crops such as strawberry (Table 1). Fresh
produce crops including leafy vegetables and soft
fruit represent higher value than commodity crops
and can help to maximise income from a limited
amount of growth unit surface. Other crops that are
frequently produced in protected horticulture systems
in Northern Europe, such as tomato and pepper,
could in theory be grown in VF systems, however
their large plant size and relatively long growth cycles
make them less appropriate candidates. In addition,
VF systems could potentially be used for the produc-
tion of non-edible crops such as ornamental flowers.
Economics
The start-up costs of VF systems are seen as a major
constraint, with site selection of high importance
(Benke & Tomkins, 2017). While VF is usually dis-
cussed in relation to farming in urban areas, and
therefore must allow for higher land prices than in
rural settings, there is no reason VF systems, particu-
larly those that adapt conventional commercial glass-
house agriculture, cannot be used in rural locations.
This can take advantage of land that is otherwise
unsuited to outdoor (unprotected) agriculture and
which otherwise may remain unused for food pro-
duction, such as waste, depleted or heavy metal-
contaminated ground containing poor or unsuitable
soil, or ex-industrial sites where the ground surface
has been replaced with concrete or brick.
The choice of rural versus urban location is an impor-
tant one. For instance, it has been estimated that the
installation of a rooftop glasshouse requires a minimum
investment three times higher than that for
a conventional ground-based glasshouse due to the
required building adaptation (Brin et al., 2016).
Similarly,thechoiceofglasshouseversusCEsystems
will affect requirements and so costs for artificial lighting
and structure construction. Useofpre-existingbuildings
for CE facilities should however, reduce setup costs
versus dedicated VF structures (Brin et al., 2016).
Banerjee (2014) analysed the economics of
a hypothetical carbon-neutral 37-floor VF facility con-
taining a mixture of agricultural and aquacultural pro-
duction. Due to the degree of stacking and multiple
harvests, the facility would be predicted to provide yields
many times higher than expected from its footprint with
an estimated food cost of between €3.50 and €4.00 per
kilogram. The study concludes that extensive research is
needed for the optimisation of the production process in
such systems in order to reduce costs and that their use
‘might be feasible’, particularly in large cities with very
high purchasing power. Unlike many other food sources,
including commodity crops, the prices for fruit and
vegetables have tended to rise (Wallinga, 2009), which
could reflect limited technological advancements and
economy of scale compared to other crops. High fruit
and vegetable prices could allow VF schemes to recoup
costs more rapidly but also, when combined with start-
up and running costs may risk prices of produce
280 A. M. BEACHAM ET AL.
ultimately being too high for many consumers, relative
to other food sources.
Environmental effects
Vertical farming systems are frequently suggested to
offer reduced environmental impacts compared to exist-
ing supply chains, for example by reducing transport
requirements through locating production in urban
sites. However, it has been calculated that of the total
greenhouse gas (GHG) emission of food systems, pro-
duction accounts for 83%, while transport only accounts
for 11% (Weber & Matthews, 2008). Furthermore, as
predominantly smaller-scale producers, VF enterprises
may lack the increased transport energy efficiency pro-
vided by larger scale and so energy use per transportation
unit may be higher (Schlich et al., 2006; Schlich &
Fleissner, 2003). In contrast, transport distances will be
greatly reduced through urban localisation and may lead
to a net reduction in transport-associated energy
requirements (Pretty, Ball, Lang, & Morison, 2005).
Construction of VF facilities will also generate GHGs
via building construction and energy use. Studies of the
energy use, GHG production, yield and water use of VF
systems are scarce. One study of the dimension optimi-
sation of a hypothetical Multi-Floor Tower design for
lettuce production with artificial lighting, water circula-
tion and solar panels on the roof and one façade calcu-
lated that the solar panels could provide sufficient energy
for the lighting and water pumping requirements of the
system (Al-Chalabi, 2015). However, the carbon foot-
print of the system (CO
2
/kg lettuce) was five times
higher than for conventional field-grown crops in the
summer and two times higher in the winter when con-
ventional energy sources were used. Increased adoption
of renewal energy infrastructure may therefore increase
the viability and adoption of VF systems.
WhilenotaVFsysteminthetruestsense,
a simulation-based environmental analysis workflow
has also been used to model GHG production in three
urban farming scenarios –a rooftop glasshouse,
a partially enclosed rooftop farm with skylights and side
windows and a completely enclosed urban farm with no
natural light (Benis, Reinhart, & Ferrao, 2017). The simu-
lation considered a large number of production factors
including site, crop, operation model, supplemental light-
ing, thermal considerations, plant growth and water use.
The results indicated that when producing tomatoes, the
rooftop glasshouse and partially enclosed system could
reduce GHG emissions by half and two-thirds, respec-
tively, versus the existing supply chain, but the fully
enclosed system was considered to have the highest
Global Warming Potential (GWP) due to the amount
of supplementary lighting required. These factors will
need to be taken into consideration when choosing VF
systems.
Energy requirements
As VF necessitates the use of a glasshouse or controlled
environment facility, so energy use may be expected to
be higher than for field-grown crops. Indeed, 58% of the
energy input for UK horticulture is used for protected
edibles production in glasshouses,whilstonly9%isused
for field crops (Warwick HRI, 2007). It has been found
that glasshouse production of lettuce uses 0.08 GWh/ton
compared to just 0.0014 GWh/ton for field-grown salads
(Warwick HRI, 2007). A model of yield, water and
energy use for lettuce production in a hypothetical
815 m
2
temperature-controlled NFT hydroponic glass-
house with supplementary lighting and water circulation
has been calculated using engineering equations based
on available data (Barbosa et al., 2015). When compared
to results calculated for conventional field production,
the hydroponic glasshouse had a 10 times greater yield
and 10 times smaller water requirement compared to
conventional production. However, the energy demands
ofthehydroponicglasshousewerearound80times
higher. Maximising efficiency in VF systems, which
also frequently employ hydroponic culture, will therefore
be key to their success, although it should be noted that
soil-free cultivation can potentially increase yields up to
10 times compared to soil-based systems (Burrage, 2014;
Savvas, Gianquinto, Tuzel, & Gruda, 2013). CE systems,
with a higher artificial lighting requirement will likely
require even further optimisation for their use to be
widespread. The ongoing balance between agricultural
land availability and energy use will likely dictate the
extent of adoption of VF in the future.
Conclusion and recommendations
Vertical Farming is an emerging technology aiming to
increase crop production per unit area of land in
response to heightened pressure on agricultural pro-
duction. By utilising protected horticulture systems
such as glasshouses and controlled environment facil-
ities in combination with multiple levels of growth
surface and/or inclined production surfaces, VF is
a technically demanding and expensive approach to
crop production. VF therefore necessitates a combined
technical approach to factors including lighting, grow-
ing system, crop nutrition, energy efficiency, construc-
tion and site selection. Whilst VF has been shown to
have potential for the production of a wide range of
crops, the technical and economic optimisation of VF
requires further attention with additional research into
maximising productivity and reducing system costs
being required. Furthermore, VF is currently industry-
led, with a large number of independent start-up com-
panies. Funding for research regarding VF at academic
institutions is limited. This hinders optimisation of the
efficiency of VF growth systems and supply chains
THE JOURNAL OF HORTICULTURAL SCIENCE AND BIOTECHNOLOGY 281
through a lack of standardisation of systems as each
VF enterprise develops its own approach. It also means
that much of the data available for determining VF
feasibility, such as crop yield, is either based on com-
mercial marketing material or conjecture rather than
scientific investigation or is unavailable in the public
sector (Pinstrup-Andersen, 2018). This situation
necessitates further research into the viability of VF
for useful scales of food production. As a sector, VF
would benefit from additional collaboration with aca-
demia in order to realise its potential and determine
the likelihood of VF sector expansion in the future as
a durable source of food production.
Disclosure statement
No potential conflict of interest was reported by the
authors.
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