How To Grow 40,000 Heads of Lettuce In A Shipping Container

How To Grow 40,000 Heads of Lettuce In A Shipping Container

How To Grow 40,000 Heads of Lettuce In A Shipping Container

Nov 19, 2017

Lettuce grows inside a converted shipping container at Tiger Corners Farms in Summerville. Tony Bertauski/Provided  |  Tony Bertauski

The weather is always perfect at Tiger Corner Farms.

Using the cozy interiors of shipping containers, the facility in Summerville farms indoors. By retrofitting 320 square feet of storage, they convert open space into a highly productive aeroponic farm. Seed to harvest, they can produce nearly 4,000 heads of lettuce in five weeks. That’s almost 13 heads of lettuce per square foot and a little more than 40,000 per year. How do they do it?

The answer is in the air.

Farming traditionally requires land. In urban areas, farming is nearly impossible where space is limited and expensive. Food often is shipped in from rural farms. What about all the space above the ground?

Tiger Corner Farms grows more than 40,000 heads of lettuce a year inside shipping containers in Summerville. Tony Bertauski/Provided  |  Tony Bertauski

Tiger Corner Farms has taken an innovative approach to vertical farming. Recycling empty shipping containers, they’ve created mobile farms that can be functional in any environment.

The process starts on a simple flood rack. Seeds are planted in coconut fiber plugs. Trays are flooded with a nutrient solution 10 minutes each day. Two weeks after seeding, seedling are plugged into hollow panels where they will grow for another three weeks. Matured lettuce is then harvested, roots and all, with no soil to wash off.

They use an alternative method of growing called aeroponics. Hydroponics grows crops in a soiless environment where roots bathe in a flowing nutrient solution. In aeroponics, roots dangle in a humid, nutrient-rich atmosphere rather than liquid. At Tiger Corner Farms, two hollow panels hang from the ceiling of a storage container. Plants are grown on both sides. The newest design has a capacity of 3,160 plants with an increased quality of product due to an improved design of locally sourced panels.

Every 10 minutes, nutrient solution is misted over the roots inside the panels. The excess solution drains to a reservoir to be recycled. An average of 10 gallons of water is used daily. Hydroponics and aeroponics require vigilant monitoring of nutrient solution. While this can be time consuming, Tiger Corner Farms has fully automated this process by adapting warehouse management software to adjust nutrient levels, pH and other environmental parameters. This system not only reduces manual labor, it tracks every crop from seed to harvest.

The shipping container is a closed system that relies completely on LED lights mounted on all sides of the panels. The light spectrum is optimized for plant growth. LEDs generate very little heat, which reduces the need to cool the container.

Besides the need for artificial light, another side effect of the closed system is carbon dioxide. Photosynthesis requires sunlight, water and carbon dioxide to manufacture glucose, or sugar. Inside the container, carbon dioxide levels drop to approximately a quarter of atmospheric levels. A propane burner is used to boost carbon dioxide and increase photosynthesis and growth.

A nutrient solution is misted over the roots of lettuce plants every 10 minutes inside shipping containers in Summerville. Tony Bertauski/Provided  |  Tony Bertauski

Once the crop is harvested, the growing panels are powerwashed and sterilized before the next planting. Crops often are rotated so that only a quarter of the container’s capacity is harvested. This reduces the demand on maintenance and delivery.

Of course, this self-contained system relies on power. Any failure in the system, whether power or a component, will alert the manager via phone or other means. In the meantime, generators keep the system running.

While Tiger Corner Farms builds the containers, Vertical Roots is the local company using them to grow and distribute the products. Currently, they provide for the Dorchester District 2 school cafeterias as well as more than 50 restaurants sourced by Grow Food Carolina.

Ashley Ridge High School in Summerville has a container on site where horticulture students assist in growing the crop. The Citadel also operates a container to provide food for the cafeteria.

Tiger Corner Farms sees its product as a way of filling a need for local produce in an urban environment. This self-contained farm can be operational in most areas and grow a variety of leafy greens and herbs.

Tony Bertauski is a horticulture instructor at Trident Technical College. To give feedback, e-mail him at tony.

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