The first phase of production for any hydroponic food crop, whether leafy greens or vine crops, is propagation. In ornamental horticulture, there are numerous propagation methods that are used to produce new plants. For hydroponic food crops, there are three primary methods of propagation: seed propagation, cutting propagation and grafting. The aim of this article is to discuss when these different propagation techniques are used, as well as key points to managing the greenhouse environment, culture and systems.

Seed propagation

Propagating young plants for hydroponic production with seed is the most common method of propagation (Fig. 1), since the clear majority of food crops can be easily grown from seed. The cost of seed for hydroponic crops varies widely across different crops. For instance, seed for some culinary herbs is extremely cheap, while seed for some greenhouse cucumbers can cost close to $1 per seed!

Seedlings are grown in either organic or inorganic substrates. Inorganic substrates such as stone wool or phenolic foam are the most commonly used substrates for seedlings. These inorganic substrates are commonly sold in sheets that have from 50 (large cubes) to more than 200 individual cells (small cubes) in the same sized sheet. Organic substrates such as ground sphagnum peat moss or coconut coir may also be used, though these loose materials need to be stabilized chemically (using glues or binders) or physically (using paper or mesh wrappings).

Closely managing the environment — moisture, temperature, light and mineral nutrients — can have a big impact on seedling production time and quality. After seeds are sown, they should be thoroughly watered in using a low-strength fertilizer solution from the beginning. While the seeds are germinating, air and substrate temperatures should be warm, ranging from ~70 to 75°F, depending on the species. After germination has occurred, air and substrate temperatures can gradually be reduced to levels similar to the grow-out environment. While some seeds need light to germinate, the intensity of light doesn’t need to be high at first. However, once the cotyledons start to expand, increase light intensity to enhance seedling growth and development. The time to produce transplantable seedlings varies with species and culture. Some lettuce can be ready to plant in as little as two weeks, and tomatoes and pepper seedlings can be ready to transplant into larger 4-inch blocks in three to five weeks.

Seedlings can be grown in a wide variety of systems and with a range of methods, all ranging widely in price, level of automation, etc. The simplest method is to produce seedlings right on the greenhouse bench or floor, like how other seedlings or transplants may be grown. Electric heat mats can be used to provide bottom heat to maintain substrate temperatures. Alternatively, seedlings can be produced in more specialized systems (Fig. 2) that are designed specifically for producing young plants.

Cutting propagation

Plants are also vegetatively propagated through cuttings for certain crops. Though seed is the most common method used for propagation, certain plants such as perennial culinary herbs are propagated by cuttings. Stem-tip cuttings are most frequently used, as opposed to root or leaf cuttings. Unrooted cuttings can be purchased from commercial suppliers or you may choose to grow stock plants and harvest your own cuttings. If you do decide to grow your own stock and propagate cuttings, be sure that you are only propagating non-protected varieties or are paying the royalties to propagate any protected varieties.

Cuttings can be rooted in the same substrates used for seedling production. While rooting hormone isn’t necessary, it can improve the uniformity of your cuttings and, therefore, your finished crop. Like any seedling production, light, temperature, nutrition and water all affect the growth and development of new, or adventitious, roots and, therefore, the final quality rooted cuttings. Since the cuttings lack roots, mist needs to be applied to keep them turgid. While the mist needs to be applied frequently in the beginning of propagation, it should be reduced as adventitious roots emerge and grow into the substrate; after seven to 14 days (depending on the species), mist may be discontinued and cuttings may be irrigated on an as-needed basis. The air and substrate temperature should be warm (~72 to 75°F) at the beginning of propagation. As roots develop and shoot growth resumes, bottom heat may be discontinued and air temperatures may be lowered. Alternatively, while some shade may be used for the first few days in propagation to help keep cuttings turgid, light intensity should increase as cuttings grow to promote root growth and reduce the time to transplanting. Finally, even though roots are not present, fertilize cuttings periodically beginning at sticking to maintain tissue nutrient concentrations, increasing concentrations as the roots develop and the cuttings start to actively grow.

To successfully propagate cuttings, the two most important components of any propagation system are: 1) a mist system; and 2) bottom heat. The mist system is vital to keep these rootless cuttings turgid; an automated system is easily the most convenient method for applying mist. Bottom heat is used much like in seed propagation — to maintain warm substrate temperatures. However, instead of maintaining substrate temperatures to promote seed germination, the warm temperatures promote adventitious root initiation and subsequent development.

Grafting

Another type of propagation method that is increasing in popularity among some hydroponic vine crop producers is grafting. Grafting is the process of combining a desirable root system, or rootstock, from one plant with a shoot, or scion, from another plant that produces desirable fruits (Fig. 3). While grafting is used to impart some type of disease resistance to plants when planted into field soils in high tunnels, grafting vine crops for hydroponic production is primarily to improve vine vigor.

The most widely used grafting method is the tube graft. It is the most commonly used method for the most popular greenhouse vining crop from seed in the U.S., tomatoes. Although grafting is considered a type of vegetative propagation, the rootstocks and scions come from young plants propagated from seed. To produce the rootstocks and scions for grafting, follow the procedures for seedling propagation and production.

One of the most critical aspects of grafting is healing, when the vascular tissues of the rootstock and the scion are connecting to allow water uptake by the scion from the rootstock. By providing the appropriate conditions, the healing period is between five to seven days.

As previously mentioned, the vascular tissues of the scion and rootstock are forming connections during this period, after which water will be able to be taken up by the roots and translocated to the shoot. As a result, the healing environment should be one that inhibits transpiration and water uptake while maintaining turgidity. Keeping the relative humidity high helps reduce transpiration and water loss, keeping the scion turgid. Additionally, since light promotes transpiration, recently grafted plants should be placed in darkness for one or two days, after which time the light intensity can increase up to ~100 µmol·m^–2·d^–1.

The take-home message

The ultimate goal of propagating hydroponic food crops is to efficiently produce high-quality young plants in a timely fashion. Whether you are using growing seedlings, rooting cuttings, or grafting plants, starting off with healthy young plants can improve uniformity and yields. Careful monitoring and management of the greenhouse environment (light and temperature) and culture (water and nutrition), coupled with the appropriate systems for the different propagation methods, will allow you to start each crop off with the best plants.

Christopher is an assistant professor of horticulture in the Department of Horticulture at Iowa State University. ccurrey@iastate.edu

At Vineland Research and Innovation Centre in Ontario, Plant Pathology Research Technician Travis Cranmer is working to analyze the efficacy of biopesticides against root diseases in hydroponic tomato production.

Cranmer’s objective is to imitate the production of a commercial grower. He uses both available biological products and those soon to be released in the early stages of grafted and nongrafted plants.

The study’s findings were released at the Canadian Greenhouse Conference in Niagara Falls in October 2016. Cranmer shares some of his conclusions below.

Produce Grower: Can you give us an overview of the bio-inoculant study?

Travis Cranmer: I’m looking specifically at microorganisms, whether they are bacterial or fungal — as well as microbial extracts — to see how they can suppress pathogen development. Our pre-commercial greenhouse mimics the same fertilizer, equipment, cultivar, media and growing practices that Ontario greenhouse vegetable growers would have. My experiment is also set up to test a wide range of products on the same crop at the same time, without contaminating plants on adjacent slabs.

We inoculated these products with biopesticides, as we know that plants actively respond to a variety of environmental stimuli. These stimuli can either induce or condition plant host defenses, to subsequently suppress infection from pathogens such as Pythium, or Fusarium, or other brute raw pathogens that hydroponic growers often have problems with.

My role is to see how they perform, so that a grower can make an informed decision when they select the product based on their growing practices, the media they use or the cultivar that they choose.

PG: Why did you decide to look at Pythium first?

TC: I wouldn’t say it’s the most severe pathogen, but a lot of growers struggle with it. It’s something that even a grower who is careful can sometimes have. It’s a relatively easy pathogen to inoculate and to monitor. We developed a [biological assessment] for it, and now we’re answering questions about Pythium with different media.

With Pythium, wilting occurs seven, 10, 14 days after inoculation. As those plants wilt following innoculation with Pythium, we record any symptom development. We take a height measurement at week 9 for the grafted, and week 7 for ungrafted plants. We do fresh weight, open up slabs, flip them over, look at root development and root rot, and we rate them on a 0 to 100-percent root rot scale. Then, we have a disease severity index that we also use.

PG: And what have you discovered about Pythium in tomatoes?

TC: We have found that we can see significant differences at the nine-week tomato harvest. It’s very likely that if we were to let the crop grow for another six months, the plants with poor root development would be stunted and have smaller yields. That’s why we test everything over so many weeks.

Our healthy controls had excellent root development, and they scored near 100 percent. And our infested controls, the grafted ones, really got swept off. But [with] the ungrafted, there were significant differences. Some of the products such as Trianum, Rootshield, BW240, had better root development and performed almost as well as the chemical control.

PG: What studies are on the horizon for hydroponic tomato pest and disease?

TC: We’re switching [the media] up. We’re basically using most of the products [from the first experiment], and a couple more. And instead of looking at grafted versus ungrafted, we’re looking at coco versus rockwool. We’re still trying to figure out which product works best for Pythium. We’d also like to know which product works best to cause suppression of whitefly or twospotted spider mite. And it’s tricky, because these biologicals don’t behave the same way in every growing media. I can’t say right now which product is our clear frontrunner, and which ones are runners up. But at the end of the day, I want to be able to help growers make informed decisions — to be able to pick the right bio-inoculant for their crop.

Editor’s Note: This interview was edited for length and clarity.

The Produce Safety Rule of the Food Modernization Act (FSMA) set a new era in food safety for produce growers. As the Food and Drug Administration (FDA) states in the Introduction to the final rule, “The rule establishes, for the first time, science-based minimum standards for the safe growing, harvesting, packing, and holding of fruits and vegetables grown for human consumption.”

With an effective date of Jan. 26, 2016, the first major compliance date (except that for sprouts) comes due on Jan. 26, 2018, which means that produce growers have 2017 to get their (green)houses in order for compliance — even many who are legally exempt.

Two of the key provisions of the rule intended to reduce what FDA assessed to be major routes of contamination of fruits and vegetables include a focus on pathogen detection and prevention in agricultural water and biological soil amendments. A brief overview of these follows.

Agricultural water quality and testing

“The overarching mandate of the requirements for agricultural water quality is that it be safe and sanitary,” says David Acheson, former FDA associate commissioner of foods and founder and president of The Acheson Group. Based on the presence of generic E. coli, which can indicate fecal contamination, the rule establishes two sets of criteria for microbial water quality:

• No untreated water or water with detectable generic E. coli is allowed for uses such as washing of hands, food-contact surfaces or produce during or after harvest, through which the pathogen could be transferred to produce directly or indirectly. If E. coli is detected, use must be stopped and corrective action taken.
• For agricultural water that is directly applied to growing produce (other than sprouts), FDA set criteria based on two values: the geometric mean (GM), of 126 or less colony-forming units (CFUs) of generic E. coli per 100 mL of water, and the statistical threshold (STV), of 410 CFU or less of generic E. coli in 100 mL of water. Further details on establishing a microbial water quality profile and tools for conducting these calculations are available through the universities of California and Arizona, with links to both at bit.ly/2jHbaIZ. FDA is also considering the publication of an online tool for growers.

Testing of agricultural water and its frequency is based on the type of source. If untreated surface water is directly applied to produce, an initial survey is to be conducted with at least 20 samples collected near harvest over two to four years. For untreated ground water applied to produce, an initial survey of at least four samples is to be collected close to harvest, during the growing season, over a period of one year. In both cases, the survey results are used to conduct GM and STV calculations. Then, after the initial survey, growers are to conduct annual surveys of at least five samples, combine those with the previous most recent 15 samples, and create a rolling database for updating the calculations.

Biological soil amendments

“Although FDA focuses on biological soil amendments of both animal origin and human waste, FDA would never allow the use of human waste on produce,” Acheson says. As such, this article discusses only those of animal origin, for which the rule addresses two key points: raw manure and stabilized compost.

FDA states that raw manure must be applied so that it does not contact covered produce during application and so post-application contact is minimized. The agency is currently conducting a risk assessment to determine the number of days that should be required between application and harvesting. Meanwhile, it “does not object” to compliance with USDA’s National Organic Program standards, which call for a 120-day interval for crops that contact the soil and 90 days for crops that don’t.

The rule also sets microbial standards for limits on detectable amounts of Listeria monocytogenes, Salmonella, E. coli 0157:H7 and other bacteria for processes used to treat biological soil amendments, including manure. Stabilized compost that meets these standards (two examples of which are given in the rule) is then to be applied in a way that minimizes contact during and after application.

For complete information on the agricultural water, biological soil amendment, and other provisions of the Produce Safety Rule, see the full rule in the Federal Register at bit.ly/2iBEdjg

Regulatory vs. customer requirements

With FDA having determined, in its 2013 Analysis of Economic Impacts of produce standards, that 956 of the 1,128 produce-growing greenhouses (as cited from the 2007 Census of Agriculture) would be considered small or very small operations, up to 85 percent of greenhouse growers could expect to be exempt from the rule or at least have extended compliance dates. However, it’s not quite that simple.

The rule does state that “farms” that have an average annual value of produce sold during the previous three-year period of $25,000 or less are exempted, and qualified exemptions are granted for farms that have food sales averaging less than $500,000 per year and whose sales to local (same state or within 275 miles) end-users exceed all other sales combined.

But, even when legally exempt, produce growers may need to comply with the rule to meet requirements of its downstream customers. That is, if you sell — or want to sell — produce to a retailer whose supplier requirements include compliance with FSMA, you will need to ensure you are following all the rules, even if you are exempted by the language of the law.

For example, in 2007, well before FSMA was introduced as a Congressional bill, Walmart created a rule that all food suppliers who wanted to sell in its stores would have to be certified to the Global Food Safety Initiative (GFSI) standards. “We saw that suppliers were trying to do the right thing, but many were doing different things,” said Walmart Vice President of Food Safety Frank Yiannas. The requirement put many suppliers well on the road to FSMA compliance — even exceeding compliance in some areas. Additionally, as found by a Walmart study which analyzed the impact of GFSI certification on product recalls, “The results suggest that a food manufacturer that achieves a GFSI-recognized certification is significantly less likely to experience a food withdrawal or recall.”

This was further validated in a presentation Acheson made at a GFSI briefing in January, in which he revealed the results of a comparative analysis of the GFSI Benchmarking Requirements V7 and FSMA’s Preventive Controls Rule. “GFSI generally meets or exceeds all of the requirements in the FSMA preventive control rule,” he said. “In some cases, GFSI has requirements not reflected in FSMA.”

With the combination of food companies requiring certification to GFSI standards and FSMA’s new supply chain control requirements, many downstream food facilities and retailers are enforcing increasingly more robust supplier requirements. “Customer requirements are often stricter and of even greater significance to a company’s bottom line than are those of our federal regulators,” Acheson says. Thus, exempt or not, produce growers can either meet the requirements or seek out another buyer with lesser requirements.

Lisa is editor of sister publication Quality Assurance & Food Safety (QA) magazine. llupo@gie.net

After staying home for several years to care for her two children, Alexis Edwards decided to find a hobby once they entered school. One of the conditions, she determined, was that it would have to be something that wouldn’t take her away from her family. That’s how Alexis started down the path to managing a hydroponic lettuce operation. Nine years later, Alexis’ hobby has evolved into a successful business that she enjoys and takes pride in, and her family has played a major role in helping shape it.

Situated on Alexis and husband Colby’s Dublin, Ga., property, R & G Farm specializes in hydroponically grown green Bibb, red oak leaf, green oak leaf, Lolla rossa and romaine lettuces. The family grows in two CropKing greenhouses, one they built in 2008 and another they built in 2015.

Alexis, who has a degree and background in teaching, has always liked to garden. A friend who was growing tomatoes in a Baxley, Ga., operation told her and Colby, who works full-time as a network manager for AT&T, about the technology. “She was so friendly and told us that nobody had a lettuce house like this in Georgia,” Alexis says.

When the Edwards first started R & G Farm, Colby called around to different restaurants and wholesale produce companies to ask what they would buy. The family started out growing and selling green Bibb lettuce, and it didn’t take long to catch on with customers. “All we did is take it to them and people fell in love with it. It’s so beautiful,” Alexis says. As requests for more lettuce came in, R & G Farm’s operations expanded.

Less-stressed lettuce

By hydroponically growing her lettuce in a greenhouse setting, Alexis has been able to produce year-round and protect against plant loss. She plants in the nursery, where it takes the seeds about a week to germinate. Then she moves the plants to the hydroponic system, where they remain for about five weeks until they are ready to be harvested.

Alexis sees more advantages to hydroponic growing than traditional soil farming. “From my experience, there are too many issues when you leave your plants out in the open,” she says. “Is it going to rain? Is there too much sun? Is there not enough sun? I can fix all that in my greenhouse. If there’s not enough sun, I can up the nutrients to get my plants to grow faster. If there’s too much sun, I can lower the nutrients so their tips don’t get burned. I have more control being in a hydroponic setting than a person out in a field has.”

The CropKing greenhouses, which measure 128 by 30 feet, utilize computers that take various measurements, and the hydroponic system continually provides nutrients to the lettuces. Some days, if Alexis is transporting, picking or sending out lettuce, she is in the greenhouses for hours. Other days, she just quickly checks on the computer and water levels, and she is out in a matter of minutes.

A family affair

Colby constructed R & G Farm’s two greenhouses himself, using knowledge from constructing a chicken house to do so. When he was a junior in high school, his family bought a property with chicken houses, and he helped rebuild them. “A lot of the dealing with the fans, motors, plumbing and electrical … all those types of questions I was pretty familiar with because of what I had done back then,” he says.

Colby’s parents’ chicken farm ended up putting him through college, and R & G Farm will afford Colby and Alexis the same opportunity for their son Riley, 18, and daughter Grace, 14. Both children helped with the construction process and still aid their parents in day-to-day operations.

At age 16, Riley played a major role in building the second greenhouse and expressed a keen interest in the process. “That was actually pretty cool because he was at the time trying to figure out what he wanted to do with his life after high school, and I said, ‘Well, it’s kind of like engineering — you read stuff, you figure it out,’” Colby says. Now a senior in high school, Riley plans on pursuing a mechanical engineering degree and becoming a commercial pilot.

Colby is glad he was able to build the greenhouses with the help of Riley, as well as Grace, who helps out in various ways such as picking and packaging the lettuce. “Family interaction has been huge,” Colby says.

Customers and confidence

The Edwards transport their lettuce to customers locally in Dublin, 50 miles north to Macon and another 30 miles farther north to Atlanta, Alexis says. Customers in Macon include several restaurants and a Kroger grocery store, and in Atlanta, Georgia Tech University and a wholesale produce company.

R & G Farm attains most of its customers through word of mouth. At the same time, it is able to offer up credentials that show it is a safe and established operation. The farm participates in the Georgia Grown program and just earlier in 2017, became Good Agricultural Practices (GAP)-certified.

In its nine years in existence, R & G Farm has dealt with its share of challenges. Among the most difficult parts of the job, Alexis says, is dealing with constant changes in the market. “One month everybody will want Bibb, and then the next month another type of lettuce will be the big hit,” she says. “Or you’ll have a customer that you’ve had for six months, and all of a sudden, out of nowhere, they’ll just want to drop you and go somewhere else.”

The fact that the family built the business into what it is now, however, has been immensely satisfying, Alexis says. Because of R & G Farm, she says she feels more empowered and is able to confidently walk in public spaces and make her presence known.

“I remember the first time I walked into the back of a Kroger, I was the only female delivering something, and I was a nervous wreck,” she says. “But I have to say, they were in awe. They were like, ‘It’s the lettuce lady!’ That’s what they called me, that was my nickname. The beer guys were like, ‘The lettuce lady’s coming.’ Then it was fun. It’s pretty rewarding.”

Patrick is a freelance writer and regular contributor to sister publication Golf Course Industry and is based in Cleveland, Ohio.