Spring is on the horizon, and greenhouses will soon be filled with annual and perennial bedding plants that are ready for retail. The first step in producing seed-propagated annuals and perennials is growing seedling plugs for transplanting into containers for finishing. Seed germination is the first step in seedling development. Germination consists of two stages: Stage 1 (radicle emergence) and Stage 2 (cotyledon expansion). In Stage 1, the seedling root or radicle emerges from the seed, while in Stage 2, cotyledons unfold and expand while the radicle penetrates the growing substrate. Once these two stages are over, germination is complete and the seedling moves into the growth stages (Stages 3 and 4, true leaf development and toning, respectively). Each stage of plug production is important and contributes to a high-quality finished plug. Germination (and the Stages comprising it) is the most crucial for growing uniform seedling plugs.

Uniform flat filling

Filling flats uniformly before seeding will improve uniformity in plug germination (Fig. 1). Cells with less substrate will dry out quicker than those with more substrate, and generally take longer to germinate due to the lower moisture around the seed. In addition to uniformly filling flats with growing substrate, ensure flats are uniformly sown or filled with seed, whether sowing by hand or using a drum seeder. While human error can cause non-uniform seeding when performing the task by hand, automated vacuum seeders can have their orifices clogged by substrate, clay seed coating and other debris, which also diminishes uniformity in plug trays.

Moisture management

Available substrate moisture is crucial to uniform seed germination. Access to water is critical for chemical and physiological processes of seed germination to occur.

However, the degree of moisture for promoting optimal germination varies among species. For instance, begonia (Begonia × semperflorens-cultorum), bedding impatiens (Impatiens walleriana), pansy (Viola × wittrockiana) and vinca (Catharanthus roseus) germinate better under “wet” conditions, whereas cosmos (Cosmos bipinnatus), dahlia, verbena (Verbena × hybrida) and zinnia (Zinnia elegans) germinate well under drier conditions. Other crops such as ageratum (Ageratum houstonianum), celosia (Celosia argentea var. plumosa), geranium (Pelargonium × hortorum) and petunia (Petunia × hybrida) germinate well under moderate moisture levels. If substrate is too dry, seeds will not germinate uniformly. Substrate moisture during germination is maintained in a variety of ways, including careful irrigation, humidity management and using a covering (Fig. 2). You should use whichever approach you are comfortable and successful with and works in your production facility. While growing too dry during germination is problematic, so is growing too wet. If the substrate is waterlogged and oxygen is unavailable to the germinating seed, radicle emergence can be inhibited and germination can be delayed.

Light

Although covering seed can aid moisture management, some seeds need covering to promote germination while others require light. Crops like begonia, impatiens and petunia require light during germination, while crops including phlox (Phlox drummodii) and vinca require covering to exclude light to improve germination. Many other species can germinate with or without light, so any covering with vermiculite or coarse perlite is more to improve moisture management for these crops.

Temperature

During germination, use temperatures warmer than those used during true leaf development (Stage 3) and toning (Stage 4). Ideal temperatures vary among species, ranging from requiring warmer (~77° F; ageratum, begonia, impatiens, vinca), moderate [72° F; cosmos, dianthus (Dianthus caryophyllus), geranium, marigold (Tagetes erecta)] or cooler (67° F; pansy, phlox) temperatures. If temperatures are too warm or too cool, germination can be delayed and uniformity can be diminished, which contributes to less-than-uniform results.

By considering all of these different factors, you should be able to improve the seed germination uniformity and get a great start on your spring crop production!

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

Nancy Rechcigl

Technical field manager, Syngenta, 30-plus years of industry experience

The very first thing is to have a dedicated person for scouting. Everyone that’s working in the greenhouse or nursery should have eyes on the crop, but having someone who is regularly dedicated to scouting the crop will find problems earlier as opposed to really seeing the symptoms down the road. When you have a scout, and you have a good scouting program, those scouts will find those problems — pests or disease — earlier. And that means corrective actions can be taken faster and that probably means fewer applications have to be made to correct the problem. It keeps the quality of the crop in a better condition. ... The other problem with not having a dedicated person is that people working directly with the crop have other duties — fertilizing, planting, etc. They can’t do a thorough job.

The second thing would be to have a plan of how you’re going to monitor the crop. Have a plan of how you’re going to approach it. Know where you’re going to start scouting and plan to alternate your scouting pattern every week, or at least every two weeks, so that you’re covering an entire area and are keeping your inspection random. ... It’s always good to carry some flags or stakes or something so that when you come across a problem in the greenhouse, you can flag it. That way, you can be sure that when you’re going to go in and do a treatment, you’re going to do a thorough job. And that makes it easier to go back and re-check the area to make sure you did a thorough job.

Jeremy Jubenville

Floriculture and greenhouse educator —Southwest Michigan, Michigan State University, 10-plus years of industry experience

There are a couple of things I think are really helpful. You should create a map of your facility — graph paper helps. And you should take that along with you as you scout, probably once a week. Some people forget to do that. I recommend using pen and paper for this because I’ve done it digitally or seen other people do it digitally. It doesn’t really stick, and they get lazy with it. Some other common pitfalls are moving too fast through the crop, misdiagnosing a disease or physiological disorder and misidentifying an insect pest. This is especially important when using biological control.

Make sure that you’re recording this in a spreadsheet and tracking numbers for different locations. This is especially important for something like thrips. When you do that, you can track trends over time. That way you know if they are creeping up, if they are spreading throughout the crop. You won’t know if you’re not keeping track of it. Sticky cards are a great tool too.

Doug VanGundy

Vice president of R&D, Central Life Sciences, 30-plus years of industry experience

Know what you’re doing — it’s got to be specific knowledge. And know the pest spectrum for each kind of plant material that you’re growing. If it’s a plant material that has a propensity towards aphids, then that’s what to look for.

Most greenhouses, in my experience, grow a variety of different plants and it takes somebody — I think it should be a dedicated individual — to be the scout. Some of these greenhouses are huge, too, so they might need more than one person dedicated to that.

It’s going to take more than one product to combat the whole pest spectrum. A grower could be dealing with mites and aphids and thrips, and they’ll need different kinds of products from miticides to insect growth regulators to systemic products to quick knockdown products. ... Identifying the pest is important, as is knowing the economic threshold of combating that pest. If you see one aphid, it’s probably not time to spray, but it gives you a heads up to say, “Well, I’ve got one. I better look around more in [the] greenhouse and look at more plants to see if they have a problem.” IPM and timing of that spray is going to be so important. ... Some years are going to be worse than others and that makes that scouting program so important. If you have a history of spider mites in your greenhouse, then having products on hand to take care of that makes sense. But these days, if you have a distributor nearby or someone that [you] have a relationship [with], you can get what you need fairly quickly.

Aaron Bivens initially got into horticulture because he loved plants, but stayed in it because of the people. As head grower at Altman Plants’ Colorado Division and head grower captain for Altman’s entire operation, Bivens combines his passion for gardening with his penchant for teaching.

“It’s a blessing to have this career because I just love plants. That’s what keeps me passionate about [this job],” Bivens says. “But day to day, it’s really the relationships. You get to see employees develop and become better growers, and that’s my favorite part.”

Here’s how Bivens keeps Altman’s growing team on the leading edge of plant production.

Farm raised

Bivens grew up on a farm in northern Illinois, where his family raised corn, soybeans, pigs and cattle. He spent summers baling hay, while helping his mom tend a garden full of everything from pumpkins to petunias.

He started college as an education major, but soon realized how much he missed growing and switched to horticulture. He earned an associate degree of applied science in greenhouse and nursery management from Kishwaukee College in his home state, and then pursued a bachelor of science in general agriculture from Oregon State University.

After an internship at PanAmerican Seed, Bivens gained several years of head grower experience at Tanasacres Nursery in Oregon. That prepared him to start his own nursery in Oregon where he sold plants to independent garden centers, farmers markets and local grocery stores for several years, until the economic decline shuttered his small business.

Bivens worked at Smith Gardens for a few years until the Altman family recruited him — first for their Salinas, California, facility, and then he moved to Peyton, Colorado, in 2015. There, Bivens oversees the 32-acre growing operation from propagation to finished material.

“I call myself a grower, but I don’t really grow anything,” he says. “I orchestrate the growing operation through coaching, guidance, protocols and training. Most of my time is spent organizing and planning to see how everything pieces together in the big picture.”

Photo courtesy of Aaron Bivens

Scouting for issues

Bivens’ growing team in Colorado consists of five section growers, each with their own assistant grower, zone irrigators and labor leads, as well as a propagation lead and other specialized positions. At peak, it’s about 65 employees.

“I don’t have the ability to meet with 60 people every day,” he says, “so I try to focus my time with the supervisors to streamline communication.”

Bivens walks every zone at least once a week with each section grower to discuss their priorities. “We use a color-coded flagging system, so if something needs to be moved, it gets a red flag. If it needs to be pinched, it gets a purple flag. If it needs a drench, depending on the rate, it gets a different color flag,” he says. Those color-coded tasks keep growers busy while Bivens moves on to other sections.

Regular scouting is vital, in Bivens’ opinion, as it dictates his approach to pest control. With people on site up to 20 hours a day, “spraying to control pests and restricting people from entry into greenhouses can be challenging,” he says. “So, we’re looking at biological pest controls and softer chemistries.”

Since Bivens came to Colorado, he has introduced nematodes and pathogenic fungi and, more recently, persimilis for spider mites and cucumeris for thrips. After a successful trial with these beneficial bugs last summer, he’s been expanding the program. “Using predatory mites seems to be very effective from the standpoint of safety, but also efficacy,” he says.

Cultivating a team

In addition to overseeing production in Colorado, Bivens also serves as head grower captain for Altman’s whole operation. He spends about 20% of his time working with the company’s other head growers to share best practices and maintain consistency.

“The idea is to be someone they can use as a reference or a resource,” says Bivens, who runs a monthly crop protocol call and frequently travels to other locations in Texas and California. “We’re spread out so much across the country that we have to get communication flowing from site to site.”

As much as Bivens loves plants, his role has revealed that his true passion is coaching other growers.

“One of my favorite things to do is to teach people,” he says. “I think it’s important for people to understand why we do things, not just how to do them. So I try to explain why we use this fertilizer versus that one — not just from the standpoint of ‘this one makes it grow more,’ but, ‘this has high or low phosphorus, so this is going to raise or lower pH,’ — constantly trying to reinforce the science.”

But as imperative as technical knowledge can be, Bivens doesn’t want employees to lose sight of the real reason behind their work.

Above all, Bivens says, he’s “trying to instill ownership and pride in the crop. It’s cool to remind your employees that all these poinsettias are going to be on someone’s table for Christmas dinner. It gives value to the job.”

The author is a freelance writer and frequent contributor to Greenhouse Management magazine.

Sunlight is free, but it’s not always available in the amount greenhouses need it. To compensate, many growers install supplemental lights. Now, research shows that dimming lights based on sunlight levels can optimize crop growth and save growers money.

Marc van Iersel, professor of horticulture at the University of Georgia, is conducting research in this area. He also started his own lighting control company, Candidus, to help growers with dimming and other lighting needs — both with LED and HPS lights.

Greenhouse Management recently caught up with van Iersel to speak about light dimming best practices and the latest in lights.

Greenhouse Management: Broadly speaking, how can dimming lights help ornamental growers?

Dimming and taking advantage of the dimmability of LEDs can help in making sure that you provide light in the amount that the plants can efficiently use when they can best use it. So, when you’re growing in a greenhouse, you constantly have changing levels of sunlight and supplemental light is used much less efficiently when you have a lot of sunlight. By measuring how much sunlight you have and making the LEDs respond to that, you can make sure that you don’t provide light when the plants cannot use it efficiently.

GM: From a daily light integral (DLI) standpoint, do you have any general figures or ranges for when additional light is no longer beneficial to plants? I know it varies by species and variety.

MvI: That’s really hard to say. One thing that we have found — and this also ties in with dimming LEDs and controlling them — is that DLI by itself may not be all that good of a guideline. We are growing Rudbeckia seedlings in the greenhouse right now, and we’re doing that with different photoperiods. So they all get the same amount of light over the course of the day — they all get 12 mols — but it’s spread out over times, I think, ranging from … 13 to 22 hours. So if you give the plants the same amount of light but you spread it out over a longer period, then you get a lot more growth. That also has the advantage that from a practical perspective, you don’t have to install as many lights. So, it decreases the capital expense.

GM: How does dimming ensure that plants get the same amount of light every day? Does the amount by which lights need to be dimmed depend on how much sunlight there is?

MvI: The dimming that we do is always in response to sunlight, but we do it in such a way that by the end of the day, the crop receives ... a specific daily light integral. But through the algorithm that we use, we make sure that that light is provided preferentially when there’s little sunlight and the plants can use that light most efficiently. One really big advantage of this precise control of lighting is that it makes production more predictable. And since in our industry, almost everything is grown based on a contract with a specific shipping date, if you know that you have good control over the environmental conditions, it becomes much easier to make sure that your crop is ready when it needs to be ready.

GM: You started a new lighting company, Candidus, with Erico Mattos, a recent PhD graduate of UGA. What is Candidus and how does the technology work?

MvI: Candidus makes lighting control systems. We don’t make lights because there are plenty of other companies that do that much better than we ever could. So, what we do is we interface with existing lighting systems. We have a really simple interface for growers where they can set the photoperiods [like], when do the lights come on, when do they go off, what daily light integral do they want? Then, our control system takes over from there to make sure that those goals are achieved. So, our initial setup was designed for dimmable LED lighting systems, but right now we’re also working on systems that can do the same with high-pressure sodium lights or non-dimmable LEDs.

GM: With Candidus, can different sections of a greenhouse be dimmed at the same time?

Yes, you can have different lighting zones.

GM: Did you say you’re looking at dimming high-pressure sodium lights as well?

MvI: No, we wouldn’t dim them, but we would turn them on and off. Some high-pressure sodium lights have some dimming capability, but it’s not like with LEDs where you can dim very precisely and immediately.

GM: In addition to the research that’s available now, what more do you think needs to be done to ensure that growers provide their plants with the right amount of light and the right types of light?

MvI: What I would really like to see — and we’re working on — in addition to having a lighting system is to have some kind of imaging system that can actually monitor how fast a crop is growing. So then you can use benchmarking techniques where you know that after 25 days, your crop should have reached a certain stage. And, if for some reason, your crop hasn’t, then you can adjust the lighting [and] environmental conditions to help that crop catch up.

GM: Is there anything else you would like growers to know about light dimming and how it can help them in their production?

MvI: I think the big advantage of dimming [lighting] systems is the predictability [they provide] and providing light when plants can best use that light. So there are energy savings associated with it as well as the big benefit of making your production more predictable.