When Plenty was founded in 2014 by CEO Matt Barnard and chief science officer Nate Storey, it was based on a core idea: Field agriculture was too unpredictable, and controlled environment, high-tech growing was a better way to supply quality food to a world that will need more of it in the years to come.

“There will be an increasing need, both for food in the world, as well as variability around the food supply,” Storey says. “We scaled up over the years. And as we’ve done that, the vision has of course not necessarily changed, but deepened, I would say, to include the idea that people don’t just need access to food, period, they need access to really good food.”

Plenty’s first farm — Storey calls it a container farm — was on the campus of a large technology company in San Francisco, and over time has grown to 100,000 square foot facilities. The business also evolved from its early days, when Barnard was using much of his own money to fund it and Storey splitting his time between his own startup — Bright Agrotech, based out of his previous home of Laramie, Wyoming — and Plenty, to receiving multimillion-dollar investments from investment groups that include Amazon founder Jeff Bezos and Masayoshi Son, the richest person in Japan with an estimated net worth of $23 billon, according to Forbes.

It was at this California-based tech company the heart of America’s currently booming tech industry, that Plenty found what worked and what didn’t in its system.

“[Starting there] basically give us time to learn, to understand the problems really clearly, and understand how indoor production can possibly solve the [problems] that we were identifying in the field,” Storey says.

How the system works

Plenty, which is currently based in San Francisco, is unlike most other vertical or container farms that grow plants on horizontally stacked shelves. Instead, Plenty uses tall poles to house the plants, which then grow out horizontally. Each pole is a few inches away from the next one, allowing crops to grow densely to the point where they essentially form a wall. The setup also allows excess heat from the lights to rise into the vented ceiling and excess water to drip down to the bottom of the plant towers and into a recyclable indoor stream, with space in front of the walls for workers to check on the plants’ health during the growing process. All of the water is then filtered and recycled back into the farm. As for harvesting, robots can handle at least part of it, but Plenty sees expertly trained human labor as a key part of its recipe.

Plenty, according to Storey, has benefited, and should continue to benefit, from the rapid evolution of growing technology.

“All of these things are dropping, precipitously, and it opens the doors for us to start leveraging that information, and those technologies, in ways that both drive costs out of our model, and make it feasible,” Storey says. “It’s true. A lot of folks who looked at this five, six years ago and said that that is not possible, they were right. It wasn’t possible that day. [It] wasn’t possible at that time, because the technology hadn’t evolved. No one — well, a few people predicted it — but very few people predicted the ways in which the economics of this business would change. And how fast it would change.”

What’s next?

The decreasing cost of technology also helps Plenty work towards another one of its goals: making its products more affordable.

“If our goal is just to produce a premium product we would be a much smaller business,” Storey says. “We would have to be content with being a smaller business. Our goal is, of course, to build a business that is global.”

A story published in Bloomberg indicated that Plenty has global ambitions and, with Son’s backing, has the financial means to expand. According to Bloomberg, Barnard has met with 15 governments on four different continents.

“It’s never going to replace the field by any means, but it’s going to become a really important part of our food production system,” Storey says. “[Our model] is stable, and it allows us to produce some of these high value horticultural products, closer and closer to people. And we just think that’s an important part of the experience, in a lot of different ways. In the next five years, 10 years, 15 years, I think we’re going to see our farms spring up all over the world. I think that people are going to be surprised at the diversity of crops that end up coming out of our farms.”

The diversity of crops is key to Plenty’s plans, which is why the company has a research and development division dedicated to developing genetics for its system because some seeds bred for field are not fit for any indoor growing system, much less one as advanced as Plenty’s. As that part of the business continues to develop, it allows the business to expand.

“We’re working both angles,” Storey says. “It’s important to us that we’re not just finding the appropriate environment for the crop. We want to grow, but we’re finding the appropriate crop and the appropriate environment. We’re kind of having this melding of both sides of the equation, and getting to the best possible place, as fast as possible.”

This article series is from the Resource Management in Commercial Greenhouse Production Multistate Research Project.

Indoor vertical farming systems or plant factories use controlled environment agriculture (CEA) technologies to grow high-value horticultural crops year-round in pre-existing urban warehouses or shipping containers. The internal building of warehouses is most often converted into a growing environment with the goal of achieving higher biomass production compared to outdoor or greenhouse production. The essential components of a vertical farm include multi-layer production shelves, hydroponic, aeroponic, or aquaponic growing systems and sole-source electrical lighting consisting primarily of high-intensity light-emitting diodes (LEDs) (Figs. 1A and B) or fluorescent lamps. However, detailed engineering design fundamentals for heating, ventilation, and air conditioning (HVAC) systems, uniformity of the environment, optimal delivery of carbon dioxide (CO₂), shelf spacing, smart lighting and shelf designs, and interaction of crops and surrounding climate in terms of heat and mass-transfer processes are often overlooked in such retrofits. Optimizing the use of resources such as energy, water, nutrients and CO2 is essential for the long-term viability of vertical farm systems, where energy intensive lighting and HVAC systems can account for close to one third of the overall operational costs. The operational costs and resource use efficiency (defined as the ratio of resource fixed by the produce to resource used by the plant; Kozai, 2013) of multi-tier-based vertical farm systems can be improved by appropriate production system design modifications for key technologies and control strategies while considering the crop-specific minimum environmental requirements such as light intensity and quality, air temperature, velocity and flow pattern, CO₂ and uniformity of these variables.

Many millennial vertical farmers are data-driven and rely on recent technology developments in sensors, environmental monitoring and control, and information and communication technologies. Integrated monitoring and control of the crop and production system and analysis on average account for about 9 percent of a farm workforce’s weekly labor hours (Agrilyst, 2017). It is expected that these technologies will further advance with integration of the diverse set of analytics platforms made available for growers and system operators empowering them to improve production quality and overall resource use efficiency. The technologies that vertical farming operations are most excited about include automation, HVAC, LED lighting systems, smart sensors and data analytics.

Challenges in vertical farming

Several economic challenges make vertical farming a difficult sector to enter and be profitable including both high start-up costs (particularly lighting, vertical growing systems, and sufficient HVAC capacity) and high operating costs (especially energy and labor). In greenhouses, labor is typically the largest production cost followed by energy. In vertical farms, energy costs may be equal to or greater than labor. In a recent survey of CEA operations, 27 percent of vertical farms reported being profitable as compared to 67 percent of greenhouses (Agrilyst, 2017).

In 2016, an energy use simulation was conducted for lettuce production in greenhouses and vertical farms in diverse climates across the U.S. Per unit of lettuce, vertical farms in Minneapolis would require 1.4 to 2.4 times more energy than greenhouse counterparts; while in an arid climate like Phoenix, a vertical farm would require five to 10 times more energy than greenhouses (Harbick and Albright, 2016). Energy use was evenly split between lighting and HVAC systems. Another simulation-based study (Graamans et al., 2018) compared greenhouses vs. vertical farms in the Netherlands, United Arab Emirates, and Sweden in terms of resource use efficiency per unit biomass of lettuce: In all cases, purchased energy (heating plus electricity) used by greenhouses was less than plant factories. Climate made a large difference in the extent of energy savings. In a moderate climate like the Netherlands, greenhouse energy was three times less than the plant factory, while in an extreme northern climate like Sweden, greenhouses used only 15 percent less energy than plant factories. However, beyond energy, it was noted that vertical farm-based production could achieve higher productivity for all other resources (water, CO2, and land area). Currently, energy costs average $8 per square foot production space and represented 25 percent of annual production costs in large vertical farms (Agrilyst, 2017). Therefore, there is further need for research on analysis of resource use efficiencies and to develop resource-conserving environmental control strategies (Fig. 2).

Automation in vertical farming

While indoor production may lend itself to increased automation (vs. field production), the nature of vertical farming (multi-layered production) appears to make it difficult to automate. Processes that in 2-D greenhouses (moving plants to the production space, respacing, sorting, and harvesting) are more time-consuming and labor-intensive in 3-D. For example, accessing crops for maintenance, monitoring, and pulling for harvesting typically requires added labor time through use of ladders or scissors lift in vertical farming (Fig. 3). Thus, automation and robotics systems need to be integrated for such operations.

Nutrient management in vertical farms

Indoor vertical farming operations take advantage of technology and automation to improve production efficiencies. This includes optimization of the root-zone (in terms of pH, fertilizer nutrients and dissolved oxygen) to produce high-quality crops and reduce nutrient waste. However, managing nutrients in vertical farming does not have to be high-tech or complicated. In addition, common nutrient management techniques used in greenhouse hydroponic and container crop production also apply to vertical farming.

Measuring electrical conductivity (EC) and pH in the rootzone are common methods for monitoring crop fertility. EC refers to the concentration of total nutrients surrounding roots, where greater EC values indicate a greater nutrient supply. pH refers to acidity or basicity in the root zone (where pH 7 is neutral), which influences the solubility and availability of nutrients for uptake. For most crops, nutrients are adequately available at pH 5.6 to 6.4. Multiple factors interact and can influence nutrients and pH during vertical farming production. For strategies on managing these factors, check out our previous Produce Grower article, “Edible crop species differ in their pH effect in hydroponics,” at bit.ly/2CNsGUk

In addition to measuring root-zone pH and nutrient levels, growers should periodically conduct detailed nutrient analyses on both the applied nutrient solution and plant tissue using a commercial lab. This helps growers check their own in-house pH and EC measurements, and verify that they are supplying individual nutrients in the correct amounts. Tissue nutrient analyses provide information on the amount of nutrients the plants are taking up, which helps growers adjust their fertilizer program for optimal plant growth and diagnose nutritional problems. Visual inspection of plants to diagnosis nutrient and other disorders remains important in plant factories but can be difficult under sole-source LED lighting. For example, under narrow waveband red and blue light, plant surfaces appear pink or purple. Some lights have a human vision feature to turn OFF red/blue light and turn ON white (broad-spectrum) light to inspect plants, or operators use special glasses with green lenses to see plants with natural colors. Computer vision systems can help enhancing plant inspection for growth, health monitoring and environmental control purposes and as an integral part of needed automation and robotics applications.

Future prospects

Vertical farming can meet consumer demand for high-quality, nutritious, chemical-free, and locally grown horticultural crops. Due to high production costs, there should be additional benefits delivered by sole-source lighting and CO₂ enrichment (such as phytochemical, nutrient or color enhancement). Research and development to improve labor and energy-use efficiency as well as increased uniformity of the growing environment will be important to address industry viability/profitability. Further, there is an increasing demand by the vertical farm industry for an educated/experienced workforce who understand both the biology and engineering of controlled environment crop production systems. Because the industry is young, the workforce has largely come from related industries without prior experience specifically in indoor climates. Therefore, it’s critical to maintain and further grow controlled environment agriculture-based research, educational, and extension/outreach programs offered by higher education institutions to meet the industry’s demands.

References

Agrilyst. 2017. State of indoor farming. https://www.agrilyst.com/stateofindoorfarming2017

Graamans, L., E. Baeza, A. van den Dobbelsteen, I. Tsafaras, C. Stanghellini. 2018. Plant factories versus greenhouses: Comparison of resource use efficiency. Agricultural Systems, 160: 31-43.

Harbick, K. and Albright, L.D. 2016. Comparison of energy consumption: greenhouses and plant factories. Acta Hortic. 1134, 285-292.

Kozai, T. 2013. Resource use efficiency of closed plant production system with artificial light: Concept, estimation and application to plant factory. Proceedings of the Japan Academy, Series B, Physical and Biological sciences, 89: 447-461.

Ying, Z. and M. Kacira. 2017. Analysis of environmental uniformity in a plant factory using CFD analysis. Presented at GreenSys 2017-International Symposium on New Technologies for Environment Control, Energy-Saving and Crop Production in Greenhouse and Plant Factory, August 20-24, Beijing, China.

Acknowledgements

Financial support was received from the USDA National Institute of Food and Agriculture, Multistate Research Project NE-1335: Resource Management in Commercial Greenhouse Production. Murat is a professor at the University of Arizona (mkacira@email.arizona.edu), Ryan is an extension professor/specialist at the University of New Hampshire (Ryan.Dickson@unh.edu), Neil is an associate professor and extension specialist at Cornell University (neil.mattson@cornell.edu) and Roberto is an assistant professor and floriculture/controlled environment specialist at Michigan State University (rglopez@msu.edu).

Genetics: The cultivated strawberry (Fragaria × ananassa) is a domesticated crop resulting from hybridizing several wild strawberry species. The vast majority of cultivar development has been focused on varieties that are well-suited to field production in mineral soils. While there have been some efforts to develop cultivars specifically for controlled-environment production, this has taken place in other counties. For growers here in the U.S., they will need to trial cultivars to identify which are suitable for their geographic location, production environment and market.

Production systems: Strawberries are most commonly produced in systems using soilless substrate, and there are several systems suitable for production. There are some containers that are manufactured specifically for hydroponic strawberry production and may be suspended on pipes or rails, or placed on top of gutters (Fig. 1). Additionally, long, continuous troughs may be filled with substrate and used for strawberry production. In addition to these systems, which are designed specifically for strawberries, smaller-scale producers may utilize containers such as hanging baskets or one-gallon nursery containers. Regardless of which system you select, a growing substrate that is very free-draining should be used. Soilless substrates comprised of organic components like coconut coir and peat moss and inorganic components like perlite are most commonly used.

Propagation and young plant production: Strawberries can be propagated in several ways. Tissue cultured plantlets can be purchased and bulked up prior to transplanting. Runners can be taken off plants, planted into small containers or cell trays filled with substrate, and placed under mist to root. Once rooted, these plants are then grown until they are sufficient size. Plants can also be dug from fields and placed into storage at temperatures below freezing until transplanting. Growers will need to propagate their own plants for production or seek out reputable suppliers of young plants.

Nutrient solution: Strawberries should be irrigated with smaller volumes of water at a greater frequency to avoid water-logging the root zone. Nutrient solution electrical conductivity (EC) can be lower compared to other crops from around 1.0 to 1.5 mS/cm, and pH should be maintained between 5.5 and 6.0 to help manage substrate pH and micronutrient availability. Specifically, strawberry plants can be susceptible to iron deficiencies, and if cooler production temperatures are used, this can be exacerbated. Strawberries also require elevated levels of potassium for developing fruits and calcium for calyces.

Temperature: Day temperatures around 75° F and night temperatures around 60° F are commonly used. While strawberries grow well under cool temperatures, growing too cool can result in long crop times. Alternatively, excessively warm temperatures (>85° F) can damage plants and reduce productivity.

Light: Strawberries can be considered a high-light plant. Using supplemental light to increase light intensity in the late fall, winter, and early spring can improve yield and fruit quality. In addition to supplemental light to increase photosynthesis, low-intensity lighting can be used to alter the photoperiod (day length) or light quality. While June-bearing cultivars flower in response to short days and ever-bearing cultivars can flower under a range of day lengths, there are some cultivars that require or are most productive under long days and, as a result, lighting is required to promote flowering when the day length is too short. Some growers use low-intensity light rich in far-red light, as this can promote flower truss elongation and allow the fruits to hang down, out from the canopy.

CO₂: Supplemental carbon dioxide (CO₂) is useful for enhancing growth in the winter when ventilation is limited and CO₂ concentrations in the greenhouse can drop and limit plant growth. Supplemental CO₂ to maintain concentrations from 500 to 1,000 ppm can be provided by burners or liquid injection.

Pollination: Strawberry flowers may be self-pollinated. However, complete pollination is important for producing well-formed fruits. Strawberry flowers may be pollinated by hand using a vibrating wand; while this is useful for small plantings, the labor-intensive nature of hand pollination may not be practical or feasible for large operations. In outdoor production, strawberries are pollinated by wind, and this can be mimicked in the greenhouse. Hair driers on the “cool” setting or hand-held leaf blowers can be used to pollinate flowers, and this is less labor-intensive than hand-pollinating with a vibrating wand. Bumblebees can be used to pollinate strawberries and are most effective for large-scale plantings, as they require minimal labor compared to any strategy reliant on labor for execution.

Pruning and training: Older, yellowing leaves are removed since they may consume more energy than they produce; the removal of these leaves also promotes air flow throughout the canopy and crowns of plants. Healthy leaves may also be removed if there is too much foliage and the plant is too vegetative. Flowers may be removed from strawberry plants that are undersized when they are first planted to promote vegetative growth and increase crown size; plants that are too small and allowed to flower will produce fruits that are too small to market, as well as slow down vegetative growth. For strawberry plants that are of sufficient size, flowers may be removed to promote fruit development. Flowers that are lower on the truss moving farther from the terminal flower, referred to as the primary or king flower, may be removed to ensure that the other developing fruits on the truss will reach a marketable size. Misshapen fruits that are not marketable should be removed to promote the development of other fruits that can develop into marketable product (Fig. 2).

Pests: Strawberries are susceptible to several insect and mite pests. Aphid feeding can distort new growth, and the honeydew they excrete can promote development of sooty mold. Spider mites can diminish the vigor of plants by damaging foliage and reducing photosynthesis. Thrips feeding can also distort foliage and fruit, and they can also transmit some diseases.

Diseases: Gray mold, or Botrytis, is the most common disease in greenhouse strawberry production and can render fruits unmarketable. The Botrytis that affects fruits can infect the plants while they are flowering and will go undetected until fruits start to develop. Avoid cool, humid conditions and maintain strict sanitation to keep crops clean. If you are recirculating nutrient solution, treat the solution to suppress pathogens such as Pythium and Phytopthora.

Physiological disorders: Deformed fruits are the primary physiological strawberry disorder. When ovaries are fertilized and seeds are produced, they produce auxin and the fruits expand. However, a lack of seed development can occur as a result of several different causes. First, the pollination of the flower may not be thorough enough. Second, pollination may have occurred, but non-viable pollen or cool temperature may have inhibited fertilization of ovules and development of seeds. Additionally, if there is not sufficient pollen for a bee population, they can become aggressive in their search for pollen and damage flowers.

Another common physiological disorder is tip burn, which can occur both on the foliage, as well as on the calyx on fruits. While tip burn on leaves is undesirable, tip burn on calyces is more problematic because it can reduce the marketability of fruit. Nutrient solution with insufficient calcium concentrations can lead to tip burn. However, conditions that inhibit transpiration (high humidity, low light) or cause excessive transpiration (low humidity) can also lead to deficiencies even when there is sufficient calcium available to plants.

Harvesting: Strawberries should be harvested every day and, during periods of warmer temperatures and high light, twice per day. At a minimum, fruits should be at least 50 percent ripe; depending on the market and supply chain, fruits can get up to 75 percent ripe. While one advantage of controlled-environment production allowing fruits to ripen more on the plant before harvest, avoid letting fruits get over-ripe on the plant since these fruits will be of lower quality once they reach the consumer. When harvesting fruits, be sure to leave the calyx attached to the fruit. Some markets may also pay a premium to have a short section of the stem or pedicle attached to the fruits, but take care when packaging so that the stem doesn’t damage other berries.

Postharvest care: Once fruits are harvested, they should be cooled to between 36 to 41° F as soon as possible after harvesting and stored in 90 to 95 percent relative humidity. While many hydroponically grown crops may be hydrocooled by submersing them in chilled water, this is not a suitable practice for strawberries; fruits can be easily damaged, and the moisture can promote disease and speed the rate of spoilage. Rather, forced-air cooling should be used to reduce fruit temperature. Clamshells with holes for ventilation or punnets are both popular packages for strawberries.

Christopher (ccurrey@iastate.edu) is an assistant professor of horticulture in the Department of Horticulture at Iowa State University.

The increase in soilless culture production of greenhouse vegetables, fruits and other consumables continues across the globe. As this rise continues, much research has been and is currently being conducted on suitable, alternative, economical, recyclable, disposable and efficient substrate materials to maximize crop yield and production efficiency. While the use of “soilless” organic and inorganic materials is not new to the industry, there is more interest in alternative materials now than ever before. Traditional (and successful) substrate components have included materials like rockwool, expanded clay aggregates, Growstones, perlite, pumice, Oasis cubes, coconut coir, peat moss and rice hulls. Another material that has been investigated is wood products (fiber, chips, sawdust, shavings, etc.). The goal of this article is to provide some background information and historical context to the development and use of wood substrates for controlled environment cropping systems. More detailed information about specific issues, potentials, advantages and disadvantages of using wood substrate materials will follow in the near future.

Wood fiber’s history

First developed in Europe in the early 1980s for the production of ornamental crops (floriculture and nursery), wood fiber has also been tested and trialed for vegetable and fruit production since the early 1990s. There are a variety of different wood components that have been commercialized over the years, many of which can have very different visual properties as well as physical and chemical properties (Fig. 1). To date, there have been more than 30 different types of wood substrate materials (components) developed, tested, and some commercialized in Europe and North America.

The idea of using wood materials can be alarming to many growers as we have been taught, or experienced, that there can be negative outcomes to growing plants in a non-composted fresh wood material. Research has shown that wood from softwood species (conifers) is better suited for use in plant growth systems because generally speaking, they do not break down (decompose) as fast as hardwoods, contain fewer phytotoxic chemicals than hardwoods, and they are located geographically around the world near horticultural production sites. Some conifer species studied in previous vegetable crop trials have included Pinus tadea, P. palustris, P. sylvestris, P. pinaster, Picea glauca, Picea abies, and Larix decidua.

Photo: Brian E. Jackson

Previous research with wood fiber substrates has been conducted on many vegetable crops in containerized or hydroponic systems including cucumber, tomato, peppers, cabbage, melons, herbs, squash, strawberries, cane berries and blueberries. These vegetable/fruit trials have spanned the globe as researchers in the United States, Canada, Spain, Poland, England, Germany, Belgium, South Korea and Mexico (as well as others) have contributed to our current understanding of the potential in wood-based substrates for crop production. Research has investigated using 100 percent wood substrates for crop production (Fig. 2) as well as blends of wood components to peat moss, bark or coconut coir.

Wood substrates currently on the market (commercialized) are primarily made by one of three main processes: 1) single or twin screw extrusion; 2) twin disc refiners; or 3) hammer mills. Each machine type and process is unique, therefore the wood fiber produced is unique. The differences among the different materials include fiber size and thickness, sterility/chemical properties, and varying abilities to be compressed, handled and blended with other materials. Companies who sell wood substrates should be able to provide the technical assistance to utilize and manage their specific product in one’s own production system. The structure and properties of different engineered wood fibers may also facilitate better or more specific usage in different cropping systems, loose-filled containers or troughs compared to compressed blocks or slabs, for example (Figs. 3 and 4).

When considering the switch to organic substrates or the switch to wood fiber in your production system, there are many variables to consider. As more intensive research is conducted, our understanding of how wood may be an option for you will become more certain. As of now, some potential advantages of wood substrate materials may include 1) organic in nature and OMRI (Organic Materials Review Institute) listed; 2) locally available to substrate manufacturers and growers, which could limit or lower transportation costs; 3) recyclable; 4) and disposable. Much remains to be learned about using wood components in our production systems, but the perceived advantages and potential are believed by many to be well worth their investigation and consideration.

Brian is an associate professor and director of the Horticultural Substrates Laboratory at NC State University. He can be reached at Brian_Jackson@ncsu.edu. More information about wood substrates can be viewed here