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Monitoring growth and development is an important practice to ensure that greenhouse crops remain on schedule and to rectify issues early in production. Clear examples of this type of monitoring are common with holiday crops with long production times such as poinsettia and Easter lily. For poinsettias and Easter lilies, a tool known as graphical tracking is used to monitor and manipulate height, while leaf counting is standard practice for Easter lilies to ensure proper timing. While methods such as these are available for a variety of potted flowering crops in the greenhouse industry, tracking the growth of young plants such as annual bedding plant seedlings is not quite as straightforward.

When it comes to the production of plugs, it is all about producing a quality crop on time while optimizing inputs (fertilizer, water, energy and fuel). Thus, it is important to monitor seedling growth during production to ensure that plugs are of good quality and their growth rate matches targeted finishing time. By monitoring seedling growth in different zones, growers can optimize inputs like fertilizer, water, energy for lighting and fuel for heating. Monitoring seedling growth manually or using destructive methods is impractical in greenhouses. One available option is to use imaging technology to noninvasively monitor seedling growth in large areas.

While imaging of crops is by no means a new technology, it has been seldom used to monitor seedling growth. Recent advances in imaging technology and software have resulted in techniques that provide increasingly rapid and accurate measurements of seedling growth. An estimate of leaf area is one of the primary measurements obtained from imaging. Leaf area can also provide a good indication of biomass accumulation, as these two qualities are physiologically connected within the plant. This makes sense when we consider the leaf as the primary site for photosynthesis. As the leaf area increases, the amount of surface area for light interception is increasing. Thus, we can conclude that as leaf area increases, more light is absorbed by the leaf and is available for photosynthesis, ultimately leading to increases in biomass accumulation. In this article, we conducted a ‘pilot study’ to test the viability of these imaging techniques in monitoring the growth of plug trays using a high-quality image station. Our future idea is to transfer this technology, if it proves viable, to simpler measurement systems like cameras mounted on irrigation booms or placed at stationary locations in a greenhouse.

Monitoring growth using imaging

To test the viability of these imaging techniques in monitoring the growth of plug trays, we conducted research using an Aris Top View Image Station (Fig. 1) located at Purdue University in West Lafayette, Indiana. The two primary objectives of this study were to 1) evaluate whether imaging could provide an accurate leaf area estimation for entire plug trays; and 2) determine if these leaf area estimations could be used to predict the dry weight of plug trays. To evaluate a wide variety of crops, seeds of pansy (Viola ×wittrockiana ‘Matrix Yellow’), petunia (Petunia ×hybrida ‘Dreams Midnight’), tomato (Lycopersicum esculentum ‘Early Girl’) and zinnia (Zinnia elegans ‘Zahara Fire’) were sown in 128-cell plug trays and grown in a common greenhouse environment. Three days after germination, one tray of plugs was selected from each species for imaging and harvest measurements. From this point, data collection occurred every two days until the leaf canopy completely closed and the plugs were considered “pullable” and ready for shipment. Software inside the image station accurately separated plants from the background (Fig. 2), which is crucial for accurately estimating leaf area. The image station was used to estimate leaf area (imaged leaf area), while the harvest measurements included leaf, stem and root dry weights as well as leaf area using a leaf area meter (measured leaf area) to test the accuracy of our imaging.

We found that a strong relationship existed between the imaged leaf area and the measured leaf area (Fig. 3), which displays that the imaged leaf area provides an accurate estimation for the actual leaf area of the plug tray. However, as leaves began to overlap later in production, it became apparent that the imaged leaf area was underestimating the measured leaf area of the plug tray. While this is an unfortunate limitation of using the imaging software, this imaged leaf area can still be used to predict what the measured leaf area would be. Additionally, we found a strong relationship between imaged leaf area and the total dry mass of the plug tray (Fig. 4). Thus, we confirmed that the imaged leaf area could be used as a means to monitor the growth of plug trays. By tracking growth in this way, we suggest that accurate predictions on plug quality can be made nondestructively.

Concluding recommendations and remarks

Our pilot study indicates that imaging technology can be potentially used to monitor growth rate of bedding plant seedlings. The imaging technology described here provides one of the most efficient, non-destructive and accurate means to do so. From these measurements, one can quickly monitor the growth of the crop and make environmental or cultural adjustments as issues or delays arise. Additionally, it is important to note that the use of this imaging software to estimate leaf area is only the beginning of what measurements are possible. By looking further into what light is reflected or re-emitted by the leaves, we can begin to anticipate and diagnose a variety of environmental- and nutritional-based stress responses. As this technology continues to be developed, we hope to present novel ways of monitoring growth and development to further facilitate optimal production in controlled environments.

Joshua Craver is an assistant professor of controlled environment horticulture at Colorado State University. Krishna Nemali is an assistant professor and controlled environment extension specialist in the Department of Horticulture and Landscape Architecture at Purdue University. Roberto G. Lopez is an assistant professor and controlled environment/floriculture extension specialist in the Department of Horticulture at Michigan State University. The authors gratefully acknowledge Ball Horticultural Company for providing seed and Jill Malecki and Zachary Oravec for greenhouse assistance.

Bell Nursery, with multiple locations in Maryland, Ohio, Virginia and North Carolina, provides fresh and local plants to customers through its partnership with The Home Depot, producing and shipping approximately 100 million plants each year.

Keeping up with this high volume has led the nursery to try a new space-, time- and labor-saving technology — Basewell Perennials by Dümmen Orange.

Bell Nursery finished its initial trial several weeks ago, says Regina Coronado, head grower for perennials at Bell Nursery’s location in Monroe, North Carolina. “It was at Cultivate that I had the idea of trying the product in 21 cell plugs.”

Before trialing the Basewell technology, Bell needed to double-handle its pots but was unable to do so. With Basewell Perennials, the grower can plant perennials directly into the finish container without having to root them, making them a consistent item from crop to crop.

The initial trial for Basewell yielded a 100% success rate. Overall, the plants each grew to their respective standards and rarely performed below average.

Basewell Perennials will allow the company to avoid the high cost and labor input of a sophisticated propagation system, according to Coronado. Likewise, more space is freed up in exchange for costly propagation equipment.

“If I could grow it under my conditions anybody could grow it, because my conditions are like from the ’70s,” Coronado says, noting that if growers don’t have the space for propagating, the Basewell technology allows them to skip that step and go directly into a pot.

Coronado is still working out exactly where Basewell fits in the operation, but Bell Nursery will be sure to include the technology going forward.

Photos courtesy of American Color

Tom Costamagna, director of growing at American Color, refers to his Orange, Virginia-based greenhouse operation as an “A to Z grower.”

According to Costamagna, spring is for packs and flats annuals, while garden mums, daisies and asters are cultivated in summer. Depending on the season, American Color also grows tropicals, vegetables and poinsettias, representing a varied plant portfolio thriving in part through chemigation.

For 15 years, the grower has been utilizing a suite of plant growth regulators from Fine Americas, a leading supplier of PGRs for the agricultural, greenhouse ornamental and landscape industries. During summer, American Color may use an ethephon PGR like Collate, which promotes branching and resets flowering in petunias, dahlias and other popular ornamental varieties. Meanwhile, Fine Americas’ Citadel product reduces plant height on a broad range of containerized crops, including the grower’s hot-selling poinsettias.

As an experienced greenhouse business, American Color tank-mixes various PGRs for optimal precision in growing.

“We use quite a bit of Collate, Dazide and Configure,” Costamagna says. He explains combinations of PGRs can also provide greater effects such as adding Abide to a Collate application to produce smaller leaves.

American Color’s primary customers are chain outlets such as Costco and Food City. Recently, the grower launched a retail partnership with Lidl, a German grocery store currently buying the operation’s annuals, though Costamagna says other crops will be added based on the season. Among other benefits, Fine’s PGRs limit potentially harmful physical interaction with the plants.

“You’re not going to be touching plants or opening a wound for a pathogen when you run a plant through a shearing machine,” Costamagna says. “In the spring, you might use Concise with PGR tank mixes, then in fall it’s Piccolo 10X that lets you finish your asters.”

Costamagna’s customers don’t want long packs and flats, instead preferring toned, shapely baskets that can’t always grow without some extra help. Fine’s focus on PGRs makes the company unique in its category, as does its products’ competitive price point. Customer service is another reason American Color has stuck with Fine for a decade and a half.

“We grow short-term crops, so having quality service available is critical to our success,” Costamagna says. “Fine listens and they follow up. That relationship resonates well with folks like me, because it’s great to know where to get something you need.”

Blooming Nursery in Cornelius, Oregon, is a wholesale grower of more than 2,200 varieties of perennials, flowering shrubs, herbs, groundcovers and ornamental grasses. They’ve been around for 38 years, and while they haven’t been using mycorrhizae since the very beginning, it’s been a staple in their production for quite some time.

Long enough that Tim Bland, Blooming Nursery’s head of propagation, was able to see the upgrade in the new MycoApply Injector Endo mycorrhizae product. Mycorrhizal Applications developed the product in response to customer feedback. Large growers and the distributors that serve them were looking for a highly concentrated product that could be applied as a drench via a horticulture injection dosing system.

The carrier was also upgraded from fine clay powder to a humic acid (which also offers a bio-stimulant effect). The previous product, MycoApply Ultrafine Endo worked in an injector, but required constant agitation and often left a clay residue in the injector tank.

Blooming Nursery applies the MycoApply in propagation because that’s where it’s most efficient. You don’t need to use as much product when you’re treating a smaller soil volume. Plus, the earlier in a plant’s life it is treated, the sooner it begins to see benefits.

“Once the fungi colonize the roots, they’re with that plant,” Bland says.

Every two weeks, the cycle begins again.

“What we’ve been doing in the past is mixing it into our soil and the flexibility that we’re allowed with the Injector Endo makes it a far superior product for our production,” Bland says. “We haven’t had to make any changes in our production line or anything to incorporate this into the mix.”

His group takes their cuttings, sticks them and “lets them do their thing.” Every two weeks new plants are propagated and hit with a drench that treats all plants at once before they head out into the cooler, drier houses. Bland likes this setup because it keeps everything consolidated. The whole process takes between 20 minutes to a half hour.

“The efficiency with which we can apply this mycorrhizae really makes it an attractive option for us,” Bland says. “A lot of nurseries are looking for ways to increase efficiency and quality at the same time. That’s what this Injector Endo allows us to do. It was a minimal, minimal change in our production and we’re super happy with it.”

Bland is also a fan of the humic acid carrier.

“All the previous injector fungi were in a clay-based carrier,” he says. “We haven’t seen any clogging or anything at all and we’ve been using mycorrhizae for a long time.”

Blooming Nursery started using the MycoApply Endo Injector in January, right at the beginning of their big spring push. The results are looking promising. The first big shift Bland saw was with Ceanothus. He noted the treatment led to a denser, stronger-looking plant with more roots on the bottom and thicker foliage on the top. The color was deeper and the plant grew in a more compact way. Another plant that had notable improvements was coreopsis, which had noticeable changes only five weeks after application.

Bland says it’s too early to give a true return on his investment — a lot of these plants are still in production. Blooming Nursery propagates but is also a finishing nursery. But he expects good things.

“I sure have that feeling,” he says. “Stay tuned, we’ll be looking at those numbers pretty closely. The implications lead me to believe we’ll see a reduction off the bat in the need for pinching and shaping.”

Using the Mycorrhizal Applications suggested grower price, the cost to treat a propagation tray with Injector Endo is a little over five cents per tray. That translates to a cost per plant in a 72 tray of $0.0007 per plant.