More research focusing on greenhouse food crops

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University researchers, some of whom previously focused on ornamental crops, are turning their attention to food crops as more growers look to replace or supplement flower crop production.

University of Arkansas horticulture professor Mike Evans said that he has seen a shift in interest by growers and students from greenhouse floral crops to food crops.

“As the ornamental side of the greenhouse industry has been undergoing consolidation with fewer but larger operations, we have seen an increased interest from the industry in growing greenhouse food crops,” Evans said. “The number of emails and phone calls related to greenhouse food crops have greatly increased. Also, more students who are interested in greenhouse production want to learn about growing food crops. Here at the University of Arkansas we put in different kinds of soilless and hydroponic production systems.

University of Arkansas professor Mike Evans is studying the production of greens in different kinds of soilless and hydroponic production systems.
Photos courtesy of University of Arkansas.

“There are a lot of people conducting research and growing tomatoes, peppers and cucumbers in greenhouses. So I started looking at greenhouse food production and found the area of greens, in many respects has been neglected. There are people out there doing these crops, but if you look for referenced research or talk to people, there is a lot less solid research on greens. In the U.S. we have tended to be field-oriented when it comes to the production of greens. Most of our breeding work has been oriented towards field production.”

Evans has started working with fellow university horticulture assistant professor and breeder Ainong Shi.

“We are interested in looking at new species of fresh greens and the breeding of greens,” Evans said. “We are particularly interested in developing crops that can take Southern hot climates. By converting our facilities to focus on greenhouse food crops we are looking to become a central institution to study new species of greens, developing new crops, breeding new cultivars, and developing production protocols for these crops.”

Evans said one of focuses of the research is to find ways that growers can easily adapt to different types of food crops without having to change their production systems.

“We want growers to be able to use the systems they are currently working with,” he said. “We are trying to find ways that growers can produce these crops without having to make any major monetary investments. In the future you may see more growers producing both ornamental and food crops together in order to be more diversified.”

Stoked on strawberries

The National Sustainable Strawberry Initiative is a new competitive grants program of the University of Arkansas’ Division of Agriculture Center for Agriculture and Rural Sustainability (CARS). The program has received $3 million in funding from the Walmart Foundation to support the expansion of sustainable strawberry production nationwide. CARS created and manages the grants program, awarding money to land-grant and other public universities with agricultural research and outreach programs.

Evans is working on several strawberry-related projects that received funding through the grants program. He is studying greenhouse strawberry production in hanging baskets, Dutch buckets and using nutrient film technique (NFT).

“I am looking at different substrates in those systems,” Evans said. “Which substrates work well and don’t work well. A large part of the project is meant to be education and demonstration. We are using the research project as a way to create a number of short videos that will be going onto our You Tube channel that is focusing on hydroponic soilless production of greenhouse strawberries. We want to create these videos to help growers who may be interested in trying to produce strawberries. They can watch these videos to learn how to go about doing it.”

For more: Michael Evans, University of Arkansas, Department of Horticulture; (479) 575-3179;

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Big on basil

Chris Currey, assistant professor at Iowa State University, is starting a research project with basil, which he said is one of the most popular culinary herbs. Currey said there are a wide variety of basils available, including Italian basils, Asian basils, citrus basils and specialty basils like the purple basils.

At Iowa State University, assistant professor Chris Currey (above) and master’s graduate student Kellie Walters (below) are working to increase the number of basil cultivars that can be grown in greenhouse hydroponic systems.
Photos courtesy of Iowa State University.

“I am going to be looking at expanding a wider palette of basils for production in greenhouse hydroponic systems, including nutrient film technique and trough systems,” Currey said. “The research is primarily going to look at the Italian large leaf basils or the pesto basils (Ocimum basilicum). These are the sweet basils. We are trying to identify more types of basil that grow well in the greenhouse.”

Currey is working with master’s graduate student Kellie Walters to broaden the number of basil cultivars that can be grown.

“We will be growing 36 varieties of basil including some of the sweet and specialty-type basils,” he said. “We are going to be evaluating their productivity in hydroponic systems. We will first be trying to identify the common commercial varieties that grow well in these greenhouse production systems.

“We will also be looking at the production methods that help to improve yields. For culinary herbs we are more concerned with the yields. Herbs produced commercially for culinary purposes are usually sold in clam shell containers of a certain weight. The growers are selling biomass, which is related to weight.”

Currey will be looking at the rate of development over a range of photoperiods, light levels, and electrical conductivity and pH of solutions for greenhouse production. He said he expects the temperature requirements will vary among the different varieties that will be trialed.

Currey said he hasn’t yet decided if taste will also be evaluated.

“Taste is a discretionary measurement based on the person eating the basil,” he said. “The characteristics that measure flavor are much more subjective. The first thing we need to determine is how to improve production. If they taste good, but don’t produce, then it’s going to be a moot point. I haven’t seen a lot of research that talks about taste or flavor because it can be difficult to quantify.”

For more: Christopher Currey, Iowa State University, Department of Horticulture; (515) 294-1917;

Climate challenges to greenhouse growing

When University of Arizona horticulture professor Chieri Kubota began working with greenhouse strawberries five years ago she said there were no grants available to work on the crop.

“At the time there were a few growers who were trying to produce hydroponic strawberries, but the production was not significant compared to the amount of outdoor production that was being done,” Kubota said. “There was some high tunnel production, but the majority of outdoor production was being done in California and Florida.”

One of the issues that Chieri Kubota and University of Arizona research specialist Mark Kroggel have resolved was determining which substrate worked best for greenhouse strawberry production.

Because of field production issues including seasonality, disease, soil fumigation, labor intensive production, Kubota looked at greenhouse hydroponics as a way to produce strawberries more sustainably.

Working with University of Arizona research specialist Mark Kroggel, the two scientists were able to get the plants to grow in the greenhouse but had difficulty getting the plants to produce fruit with commercially acceptable quality.

“The lack of fruit production was related to the climate conditions that we have here in Arizona,” Kubota said. “Mark Kroggel and I applied for and received funding from the National Sustainable Strawberry Initiative. Our goal is to teach growers how to hydroponically produce greenhouse strawberries in a semi-arid climate like Arizona.

“Our whole approach was to start with a production system that had already been proven to work well and that was widely used. We wanted to start with reliable technology because we wanted to develop a program and to teach others how to do it.”

Chieri Kubota is working with LED lights to determine their effect on grafted plants to produce strong seedlings that are easier to graft.

One of the issues that Kubota and Kroggel have resolved was determining which substrate worked best for greenhouse production.

“Strawberry roots require a lot more oxygen compared to other greenhouse crops like cucumber and tomato,” she said. “If there isn’t an adequate amount of substrate porosity the roots don’t develop properly, which affects the overall growth and the fruit production. Strawberries also take up a smaller volume of water than other greenhouse crops such as tomato and cucumber so the root zone environment is largely affected by the chemical and physical properties of substrates. Strawberries can also have issues with pH that other crops don’t experience. We ended up choosing a substrate consisting of 50 percent perlite, 25 percent coconut coir and 25 percent peat moss.”

A physiological disorder of strawberry that Kubota found to occur in the semi-arid climate of Arizona was tip burn caused by calcium deficiency. Symptoms appear on the leaves and on the calyx and can lower the market value of the fruit.

“We determined that the plants require a high humidity at night to supply enough calcium by root pressure,” she said. “We are testing an under bench misting system to raise the humidity during the night so that calcium is provided to the fruit. This technique has nearly eliminated the problem with calyx tip burn. The mist is supplied for three hours at night under the benches, so the water doesn’t land on the plants. The next day the added moisture is evaporated so that the plants are not being grown under a high humid environment all of the time.”

Kubota is also working with LED lights to determine their effect on grafted tomato and watermelon plants. She developed a new application of LED lighting to produce strong seedlings.

“When doing grafting the plants need to have a little more stretched growth. That stretched growth can be difficult to achieve,” she said. “By providing the plants a small amount of light with specific wavelengths at the end of the day causes an extension of the stem. A few days after providing the light treatment the seedling has a good length of stem so that it is easier to graft.”

For more: Chieri Kubota, University of Arizona, The School of Plant Sciences, Controlled Environment Agriculture Center; (520) 626-8833;;

David Kuack is a freelance technical writer in Fort Worth, Texas;

2 thoughts on “More research focusing on greenhouse food crops

  1. Hello Again,

    Thanks for replying us with your questions. regarding your questions, the client provides me the answers as following:
    What are you planning to grow (only lettuce)?
    No, she is planning to grow multiple crops and fruits e.g. tomatoes and pepper.

    Is land available and what sizes?
    The land is available, but not owned yet. The size should be 1000 m^2.

    What is the exact location of the site (to analyze the climate conditions)?
    the location is in Jeddah coast (the climate is hot and the humidity is high).

    Is there infrastructure available on the site, like roads, water, electricity and natural gas?

    What is the available budget for the project?
    200,000 SA

    What business is your company now dealing in and do you have experience with greenhouse?
    She is a beginner businesswoman, and she hasn’t experience with greenhouses.

    And other information that can be of help to us. The more information we receive the better we can serve your demands.
    She mentioned a concern with the high humidity in this location which is a critical problem for the greenhouses. Also, she needs to see a preliminary project model (initial design of this project). Finally, she is enthusiastic to start a project in cooperation with your company.

  2. Dear Aisha: We recommend that she contacts a company like Crop King or American Hydroponics. Both companies can offer turn-key solutions which should fit her budget and her utlimate goals.

    If she wants to go more high-tech and wants to put her own team together, we recommend Hort Americas. They can work with her in a team environment to build her project. Unfortunately her budget will need to be increased.

    Thank you.

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