Interest in growing hydroponic strawberries has come from both ornamental and produce growers.
Photo: iStock.com

In Japan, greenhouse-grown strawberries are sweet and packed with flavor, says Dr. Chieri Kubota, a researcher at the University of Arizona’s Controlled Environment Agriculture Center (CEAC). But here in North America, 90 percent of the strawberries we consume are field-grown in California or Florida, and the taste experience isn’t quite the same, she says.

Kubota, who is originally from Japan, says, “The flavor of [field-grown] strawberry [in the U.S.] is very, very different than what I knew from my home country [Japan]. Very hard or firm, and then very tart — less sweet. But [they] store very well.”

Kubota has used her extensive background in controlled environment agriculture, along with her native Japanese language, to study Japan's strawberry research and build on it at CEAC.
Photo courtesy of Chieri Kubota, University of Arizona

Why grow hydroponically?

As interest grew in local production across the country, Kubota began researching hydroponically grown strawberries in 2009, as an unfunded side project from her tomato research at CEAC. Kubota and her team use about 500 square feet of greenhouse space to study best practices and production methods.

Eventually, she garnered support from a Japanese company, which helped lend its styrofoam troughs to CEAC, as well as access to a huge amount of information on the topic published in Japan. Kubota was at an advantage to experiment based on this research, as she speaks the language natively and can read the studies.

Over 53% of seven to nine year olds picked strawberries as their favorite fruit. – University of Illinois Extension bit.ly/2adZESg

And what she found through this research and her own trials is that unlike tomato, cucumber and other popular greenhouse-grown crops, it takes much more time to fine tune strawberry production methods for best flavor and yield.

“I quickly realized that it’s a very complex physiology [that] the strawberry has, and that it’s not an easy crop to learn,” Kubota says. In fact, she says growers likely won’t have the preferred production methods down pat until after about six growing seasons — which is about three more than tomatoes, cucumbers and lettuce.

During the first three to four years of research, the CEAC team made mistakes, and implemented many improvements to the production system. Now that they’re about six years in, they’ve begun distributing information to train and consult growers so that they don’t repeat those same errors. Much of this information can be found at ceac.arizona.edu/strawberries

Changes in flavor

When comparing the flavor profiles of hydroponic strawberries and field-grown strawberries, Kubota says that hydroponic strawberries may not be perceived as having as much flavor. However, the perceived flavor difference is not necessarily problematic, she says, as hydroponic berries offer additional benefits that field-grown fruit doesn’t.

“Fruits are hanging in the air in hydroponics, because they usually use a raised bed or raised trough. So fruits are not touching soil. The shelf life or fungal disease incidence is much better because fruits are clean,” she says. And while she hasn’t yet experimented with producing organic strawberries in a hydroponic system, growers have told her that they have experienced an improvement in flavor by using organic amino acid fertilization.

Kubota also believes that with more research toward better management in irrigation, the taste difference can be reduced.

Challenges and research focus

In addition to flavor, hydroponic strawberry production presented its own set of challenges. Finding a good substrate was the first.

“Important characteristics to select a good substrate for strawberry are, No 1., good drainage,” Kubota says. “Strawberries don’t like wet soil or wet substrate. Then also, we have to select something porous, so that means air space between the particles.” The group has selected a coconut coir mix that works well.

When it comes to planting, Kubota says that transplanting in early September, with well-established plants, is best. That means, vegetative plants should have four to seven “true leaves” with flower initials already present in the meristem. “First harvest is usually in two months,” Kubota says. “Then we want to target the early- to mid-November to begin harvesting, because Thanksgiving is coming up.”

California and Florida combine to produce 91% of strawberries in the U.S – National Agricultural Statistics Service bit.ly/2ac0yyP

However, the challenge is that in the U.S., few field growers have planting materials in the summer months and early September. “Because U.S. strawberry transplant production is, again, toward the open field, plants are harvested in the fields of northern California during the winter time, then stored at chilling temperatures, minus 2 degrees Celsius, and then they can’t store beyond June of the following year,” Kubota says. The disadvantage to hydroponic growers is that they must begin with plants of a lesser quality, or propagate in their own greenhouse with permission. Yet, many modern varieties are still patent-protected — so if growers do decide to propagate on their own, they must do so with varieties that are 30 to 40 years old or get the license to propagate their own, she adds.

Additionally, the research team at CEAC has been and is continuing to learn how to control the physical disorder that can appear when growing hydroponic strawberries in low humidity — in climates like Arizona, for instance. As soon as October comes, strawberries begin showing what’s called tip burn — a brown pigment around the leaves of the fruit that’s caused by a lack of calcium. To prevent tip burn, the team began covering the plants at nighttime, which helps keep them humid during the hours they like to be. But now they’re looking into new ways to adjust humidity levels — as this is a labor-intensive practice.

Additionally, no crop comes without its susceptibility to pests and diseases. For strawberries, the threat is spider mites. CEAC manages spider mites by releasing a predatory mite for biological control, which Kubota says can be beneficial if done as a proactive measure.

Disease-wise, powdery mildew is a challenge, and CEAC is still looking for effective control.

Who’s growing?

Hydroponic strawberry fruits tend to be cleaner than field-grown strawberries, as they hang from troughs and don't touch soil.
Photo courtesy of Chieri Kubota, University of Arizona

Kubota says the interest has come primarily from those who have already been using greenhouses — like growers in the ornamental market, those growing tomato and lettuce under a controlled environment, or even people who are completely new to the industry who want to do local production in vertical farming-type settings. But she says more support needs to be given to strawberries grown in a controlled environment.

“Nursery capacity needs to be developed very rapidly to catch up with growers’ interest, particularly offseason production,” Kubota says.

Chris Manning also contributed to this article.