Growing mixed greens at the largest aquaponics facility in the world

Very unique greens are growing right now in a greenhouse in Hixton, Wisconsin.

These greens are distinctive in several ways — first and foremost, they float on a rather large water tank of 850,000 gallons. Indeed, they are located at what the company says is the largest aquaponics facility in the world and utilize salmon waste in their growth. They are also certified organic.

Superior Fresh has been growing various greens and Atlantic salmon since 2017 with an eventual projected greenhouse harvest of 1.8 million pounds and fish harvest of 40,000 pounds per year. The greenhouse is quite large (123,000 square feet with more than 1,100 LED lights) and employs 40 people, including the adjacent packaging facility.

Baby romaine, spring mix, head lettuce, red leaf lettuce, swiss chard, bibb and green romaine are currently being marketed by Superior Fresh to various retailers, schools, hospitals and restaurants between Minneapolis and Chicago. “Our goal is to keep everything within 400 miles of our farm so that our customers get the freshest product possible,” says chief operating officer Brandon Gottsacker. “We currently package both washed and raw product in plastic clamshells, bags and wholesale cases.”

Semi-decoupled system

Some aquaponics systems have a setup wherein the plants grow in floating beds right in the fish tanks, but Superior Fresh uses what it calls a semi-decoupled system. The system has interconnected but separate greenhouse and aquaculture operations, with the same water usually flowing through both, then cleaned and recirculated. Gottsacker says there are several benefits to this system. “It allows us to have a large-scale, high-production environment for completely different organisms, fish and plants,” he says. “In addition, water parameters ranging from temperature to nitrates and micronutrients are measured and adjusted as needed, but in our setup, we have the option to completely decouple the systems. That is, we can circulate the water continuously or control the greenhouse environment independently from the fish system but still utilize all the available nutrients from fish waste.” The plants are grown in standard floating foam boards, which Gottsacker and his team are optimistic will last for years.

Superior Fresh head grower Adam Shinners says running an aquaponics greenhouse in Wisconsin had initial challenges with fine-tuning the nutrients, handling pest and disease pressure and also managing light, but at this point, he and his team have had many months to optimize processes. The goal, as it is in any greenhouse, is to achieve a consistent environment to ensure consistent product, but it’s obviously more complex due to the fish factor. Shinners had had to ensure that the nutrient mass balance between fish waste load and plant uptake is accurate, consult with pest and diseases experts to ensure good management practices minimize risk, and work closely with Superior Fresh’s LED supplier to help understand the best lighting strategy, “with plant yield, energy consumption and plant morphology in mind.”

The pests that Superior Fresh greens have had to contend with include mites, thrips and aphids, all of which must be controlled using beneficial insects in order to maintain organic product certification. “We are currently using Swirski mites and Chrysopa as our beneficial insect of choice to control for thrips and aphids,” Shinners says. “This practice is seasonal and pressure-dependent. When the pressure is low to undetectable during the winter months, the usage is discontinued. When pressure increases during the summer months, using these beneficials seems to control the population of these pests very well.” With all that water in the greenhouse, mildew is another challenge, but it’s being addressed well with precise humidity control and the use of preventative biological fungicides. These are sprayed through an atomizer, Shinners explains, ensuring good leaf coverage while using a minimal amount of product.

Production challenges

At the same time Superior Fresh has handled the basics of greenhouse production, the greenhouse team is also working to ensure the right varieties are grown at the right times of year to maximize quality and yield. “We have been testing varieties for over a year now, so we are slowly collecting data as to which varieties we should grow at certain times,” Shinners says. “We offset the natural decrease in biomass during the winter by injecting carbon dioxide into the air and extending the photoperiod to 20 hours using our LEDs.” The LED spectrum provided is suited for greens production: blue and red wavelengths, at a rate of 12 to 14 mols, depending on how much sunlight is available on a given day.

Water for the greens is drawn from two wells on the property, flowing first to the fish and then to the greens, with 99 percent recirculation. The remaining 1 percent is removed along with fish waste and used to irrigate alfalfa fields onsite. All fish processing waste and greenhouse waste is also composted onsite and applied to these same fields. An ozone system is used to treat the water, but only unwanted bacteria are targeted. “Beneficial bacteria are a very important piece of the puzzle when integrating fish and plants and we do not want to kill them,” Gottsacker explains. “The ozone helps flocculate the solids, which helps keep the water free of unwanted or unnecessary bacteria.”

The nutrient level from the fish waste is very consistent and now displaces about half the fertilizer that would otherwise be required on an ongoing basis. Initially, however, Shinners says the fish waste was not high enough in macronutrients to meet the demands of the greens. This has changed as the fish matured and feeding rates have increased, and some micronutrients are added into the greenhouse fertigation system.

In terms of other hurdles, Gottsacker says one of the biggest has been, “trying to get buyers and/or distributers to understand what we are offering. … Many buyers have a difficult time changing their conventional ways. All of our customers have been incredibly responsive to this futuristic style of growing and truly enjoy coming to see the farm and all the foods that we are producing. The hardest part is getting the attention of buyers and getting them to make a change as well.” He adds that because salmon are a coldwater fish species that require very good water quality, keeping that in check “requires constant monitoring and is incredibly challenging.”

Gottsacker gives huge credit to the staff. “Everyone here puts in farmer’s hours when needed no matter what day of the year it is,” he says. People with farming mentality were hard to find, but today we have a great group of people onsite every day that do a great job keeping our fish and plants thriving.”

He adds that if Superior Fresh only focused on a few varieties of lettuces, it could hit its goal of 1.8 million pounds a year very quickly. However, Gottsacker explains that “we as a team have the vision to grow what people want. … This vision comes with some production volume sacrifices but shows our customers that we can grow them what they want.” He notes that standalone aquaculture systems, especially for salmonids, take two or more years to see any cashflow, but by farming both fish and plants, Superior Fresh was “able to alleviate the long lead time to positive cashflow with produce sales early on in the development of the business.”

Looking forward, Gottsacker says that “as people begin to recognize the positive benefits that comes along with growing food the way we do, they become life-long customers.”

Treena is an Ontario-based national and international award-winning writer who focuses on science, technology and industry issues.