Growing hydroponic strawberries in thedesert4 December 2013, by Donna Kreutz

Hydroponically grown strawberries stay clean hangingthree feet above the ground in the UA’s strawberryproject greenhouse. Credit: Chieri Kubota

Growing up in Tokyo, Chieri Kubota savored freshstrawberries brimming with flavor in the winter.Only when she went to college and studiedagriculture did she learn that fresh strawberries inwinter are "an unusual cycle against nature," shesaid.

Today Kubota is trying to perfect that off-seasoncycle and grow strawberries hydroponically in agreenhouse in the University of Arizona ControlledEnvironment Agriculture Center, which is part ofthe College of Agriculture and Life Sciences. Hergoal is to introduce sustainable strawberrycultivation to local greenhouse growers andprovide sweet luscious berries for restaurants, high-end grocers and farmers markets.

She knows it can be done. "I'm from Japan. Wegrow strawberries in greenhouses in winter." Someare grown hydroponically.

Kubota is a widely published professor in the UASchool of Plant Sciences and the Department ofAgricultural and Biosystems Engineering. Shecompleted a doctorate from Chiba University inJapan, did post-doctoral research training atClemson University in South Carolina and LavalUniversity in Canada, then joined the faculty of heralma mater. She came to the UA in 2002 to workwith hydroponic tomatoes and explore the potentialof adding sustainable strawberries to localgreenhouse production.

In the United States the majority of strawberries aregrown in California. The plant varieties – or cultivars– are bred for that climate. In the desert, even in agreenhouse, it's a challenge to approximate thatmild misty coastal climate.

Kubota's co-principal investigator on the project isresearch specialist Mark Kroggel, who has aMaster of Science degree in horticultural science.Kroggel designed an under-the-bench fog systemthat releases humidity at night so the strawberriesare dewy moist by dawn. It's turned on for fiveminutes at time, three times an hour, for threehours. This is "technology to make the plantshappier," Kubota said.

Focus on Flavor, Not Shelf Life

"We want water flowing into the plant all the way tothe tip," Kroggel said.

If water doesn't reach the tips of the leaves at night,they get tip burn. Those lovely green petals aroundthe base of the strawberry – called the calyx – alsocan turn "an undesirable crispy brown that affectsmarketability."

"He's the grower," Kubota said. "I'm more the 'idea-theoretical-based person.' So I think – and hemakes it happen."

They experiment to identify optimal growing

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conditions for sustainable off-season hydroponicstrawberries. "We want the strawberries to growslower in the right conditions so they accumulatesugar in the fruit," she said.

"Flavor is very important. We want to see flavorover shelf life," Kubota said – because theseberries don't have to travel very far. They'll be soldlocally.

Strawberries ripen in the UA strawberry projectgreenhouse. Credit: Chieri Kubota

The California cultivars are bred for yield, shelf lifeand disease resistance, she said. Flavor is maybefourth on the priority list.

Strawberries are harder to grow hydroponicallythan tomatoes or lettuce.

"Most traditional greenhouse crops are quitepredictable," Kroggel said. "Not strawberries."

At this point they're a low-yield, high-maintenancecrop.

The humid strawberry greenhouse is bathed inbright diffused light. Plants are growing in specialstyrofoam troughs from Japan that maintain ahealthy temperature. The troughs are suspendedby chains in long rows at waist height. Bright redberries peek out from lush green leaves.

"This type of production is rarely done in the U.S.,"Kroggel said.

New Varieties to Share with Growers

In Japan, which produces some 259 million poundsof strawberries annually, new flavorful varieties arepatented like drugs.

"We recently got some off-patent plants fromJapan, but their condition was not so good," Kubotasaid. "Now we're in the tissue-culture stage to getbetter plants, healthier plants. Next year we hope toplant them in the greenhouse. This is not a high-yield variety – but it is really flavorful," she said."These are relatively old varieties that we hope wecan propagate and share with growers."

There is an astonishing lack of informationavailable about growing greenhouse strawberries –one reason this UA research is so valuable.

Research specialist Mark Kroggel (left) and graduate

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student Michael Whalen work on strawberry plants in theUA greenhouse. Credit: Chieri Kubota

The literature includes one book from New Zealandcalled "Hydroponic Strawberry Production," byLynette Morgan and a thick tome of severalhundred pages written in Japanese. There's oneUA library book from 1932. There's not much morethan that.

Recently a collaborator in Oregon came across astrawberry crate label from 1943 that read "Arizonamade, packed and distributed." Then Kubota met aJapanese-American woman who said her familyhad grown strawberries in Phoenix. That led her todo more research and discover that Arizona grewstrawberries in the winter back in the 1890s.

C. B. Hewitt of Pasadena, Calif. wrote in a letter tothe editor of the Pacific Rural Press in 1897:

"While visiting Phoenix, Arizona, during January,1893, I noticed some fine large, bright red, glossy strawberries in the market and upon inquiring wastold that they were originated a few miles out fromthe city and were called the Arizona Everbearing. Iat once drove out to see the patch and wassurprised to see the quantity of fine ripe fruit...

"I purchased 2,000 of the plants from the originalgrower and planted them out in Pasadena. ... TheArizona ... is the most prolific and luscious berry yetproduced on the Pacific Coast ... continuing to bearenormous sized bright red berries that fairly melt inthe mouth for at least eight and sometimes ninemonths of the year."

Sadly the Arizona Everbearing Strawberry is nomore. Yet it inspires Kubota and Kroggel to knowthat there once was strawberry cultivation inArizona and – with their high-tech hydroponicsresearch – it could happen again, in a much moresustainable way.

Right now they're growing three California varieties.This winter – their sixth year – the greenhouseplants have the potential to be very productive.

"We may have to pick every single day," Kroggelsaid.

Provided by University of Arizona

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APA citation: Growing hydroponic strawberries in the desert (2013, December 4) retrieved 5 June 2019from https://phys.org/news/2013-12-hydroponic-strawberries.html

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