Watering greenhouse crops is arguably one of the most important tasks at any production facility. How and when crops are irrigated affects plant growth and development, and ultimately, finished plant quality.

Irrigation also affects other aspects of production, such as plant diseases, and water- and nutrient-use efficiency. The manner in which crops are watered also can have a large impact on labor costs. There are a variety of ways to irrigate greenhouse crops, and this article is going to focus on subirrigation and some of the tips and tricks or best management practices to keep in mind.

Overhead irrigation, where water and nutrient solutions are delivered by hand with a hose or automated from a boom, is the most common form of irrigation.

Drip tubes or drip emitters irrigate on the surface of the substrate, and are also widely used. Subirrigation is a technique where water or nutrient solution is provided to the bottom of the container and is absorbed or taken-up into the growing substrate by capillary action. There are a number of different methods of subirrigating plants, including ebb-and-flood benches or Dutch trays, flood floors, or capillary mats.

While these different subirrigation systems vary in their cost and lifespan, providing options for any scale of production, the principles of using any subirrigation system remain the same for all of them.

Why use subirrigation for growing greenhouse crops? There are a few advantages to taking this approach. First, subirrigation can help minimize diseases, specifically foliar diseases. High humidity and free-standing water promote diseases such as botrytis and powdery mildew. Overhead irrigation leaves foliage wet, and drying is promoted by watering early in the day and allowing sufficient time for foliage to dry, as well as through the use of horizontal air flow (HAF) fans. With subirrigation, foliage stays dry regardless of irrigation. Subirrigation also allows for more flexibility in timing irrigation — watering crops later in the day won’t run the risk of wet foliage going into in the evening.

Aside from minimizing foliar diseases, subirrigation can improve plant quality. As previously mentioned, water or nutrient solution is taken up by capillary action in the root zone until the substrate is saturated. Compared to overhead irrigation, where the same, or a similar, amount of water is applied to each container regardless of how wet or dry it is, subirrigation allows containers to absorb varying amounts of water until they reach the same saturated level, improving uniformity across the crop.

Subirrigation is also flexible and accommodating for different crop spacing. Whether it is shuttle trays of 4-inch containers placed pot tight or 8-inch poinsettias on 18-inch centers, it doesn’t matter for subirrigation. This flexibility makes the switch between crops throughout the year seamless and easy, especially when compared to using drip tubes and emitters that have fixed spacing.

Finally, like any form of automated irrigation, labor savings can be significant for subirrigation systems. By eliminating hand watering, subirrigation allows for hundreds to thousands of plants to be irrigated at the same time, depending on the size of the subirrigation zone.

There are some cultural practices that will have to be modified or monitored carefully when using subirrigation, regardless of which system is used. First, fertilizer concentrations have to be reduced. Whether it is water-soluble or controlled-release fertilizer, less is required with subirrigation. Since water moves up into the container through capillary action, there is virtually no leaching when crops are subirrigated.

Although this can be considered a good thing, especially to improve water- and nutrient-use efficiency and avoid unwanted runoff, there is no opportunity to leach excess fertilizer salts out of containers and reduce electrical conductivity. Using less fertilizer will help avoid supra-optimal substrate ECs and still provide sufficient nutrients for plant growth. By how much should fertilizer concentrations be reduced? A good place to start is to reduce concentrations by 50% compared to what would be used in overhead irrigation. When in doubt, err on the side of less fertilizer. Plants can always be provided with higher concentrations of water soluble fertilizer (WSF) to increase substrate EC in subirrigated systems, but providing too much may be challenging to deal with.

Another consideration for subirrigated systems, especially those that are capturing and recirculating water and nutrient solutions, is excess pesticide runoff, including plant growth regulators (PGRs), insecticides and fungicides. When these solutions have the potential to be recaptured in the same reservoir where water and nutrient solution is stored, the active ingredients can be taken up during subsequent irrigation events. Ultimately this can lead to unwanted and/or excessive applications of these chemicals. When drench applications are made to containers grown in subirrigated systems, try to minimize any leaching of pesticide solutions out of the container. Similarly, avoid excessive runoff from canopies and applications to floor or bench areas.

Finally, sanitation should be a priority in any subirrigation system. While greenhouse sanitation is important for any operation, regardless of their irrigation system, it takes on additional importance for subirrigation systems where water and nutrient solutions are captured and reused. Diseases are generally not going to be transmitted plant-to-plant via transmission in subirrigation systems, as the water is taken up by the substrate and no leaching occurs. However, if pathogens are introduced into the water from other means, such as infected plant materials laying on the bench or floor, then infested water that is recirculated and provided to plants can cause diseases to spread quickly.

Maximizing crop quality and minimizing labor are common goals for any greenhouse grower. Regardless of what scale you are producing on, there are subirrigation strategies that can fit your facility and budget. The best management practices outlined in this article can help deliver optimal results with subirrigation systems.

Like any Millennial, I’d heard of FOMO (Fear of Missing Out). But FORO? That was new to me.

Allow me to explain.

I was in Grand Rapids, Michigan, last week for AmericanHort’s inaugural Finished Plant Conference, which turned out to be a two-day (and, at times, quite technical) deep dive into all aspects of plant production when taking them beyond the young plant (aka liner) stage.

I don’t have room here to cover everything that went down in Beer City, USA — which honestly seemed a bit like a ghost town still due to COVID — but I can relay a couple nuggets I picked up:

Natives and pollinator-friendly crops are still scorching hot with plant buyers, and they will likely continue to be so into 2022.

Succulents can be incredibly profitable if you commit enough greenhouse space to scale up production.

Something else that has remained stuck in my craw, though, is this new-to-me concept of FORO, or Fear of Running Out (of plants to sell). It was briefly mentioned by a grower lamenting that we’re often so hyper focused on bottom line sales and revenues and pleasing every customer, that sometimes we act like selling out of a plant or a variety is the end of the world.

His point was that, well, maybe it’s not always such a bad thing. Because that’s also confirmation that you’re growing the right type of plants and doing so in a way that your customers seek out, time and time again.

And I don’t have to tell anyone here, oftentimes that’s half (or maybe it’s closer 33%?) of the battle.

Bottom line: Don’t let FORO influence your buying this season. Trust your data and focus on the plants that are consistently selling out each season. It’s a good thing!

Happy Thanksgiving!

Photo courtesy of Suntory Flowers

Greenhouse Management: What was your reaction to you finding out you would get this role?

T. Jay Higgins: I was surprised myself that I was going to work for someone, really. [Laughs] I never thought I would accept something like this. The relationship with Suntory has always been good, always been strong, so it wasn’t surprising that we would want to strengthen the relationship [even] more ... This was a really good opportunity to do something different. I started Sunfire Nursery in 2005 and have been doing the same thing for a long time and I’m excited for a new challenge and a chance to learn another side of the business.

GM: What, in your mind, makes Suntory products something you trusted as a grower and something you are going to work on even more?

TJH: Performance — the garden performance. Usually, they have the best garden performance. As everyone knows, they are not always the cheapest genetics, but they perform better in most cases. In my time working with them, they’ve always had strong plants and an excellent breeding team, and I feel confident that they’ll continue to debut good stuff down the road. Part of the reason I took the job is that I’ll have exciting products to work with and opportunities to work with clients in good situations.

GM: With how strong sales have been the last 18 months or so, where do you think the markets you’ll be working in are at right now? And what will you focus on when you start officially with Suntory?

TJH: I think the markets are still in a good spot. I personally believe that, over the next couple years, maybe it will have a slight downturn. Maybe we won’t be able to keep up the crazy growth we’ve had over the last 18 months or two years even. But if anything, we’re seeing more and more people being excited about gardening. More and more people are out there taking care of their houses and buying plants and that can only be a good thing. The other thing down here in Florida and other places, too, is that the housing markets are crazy. That historically has driven plant sales, too. And when I get started, I’m going to get to know partners, get to know the cutting farms, the processes. There’s a lot to learn. I’m still able to go to the cutting farms in Mexico and whatnot, and I’m really excited to do that.

With fuel prices having crossed the $3 per gallon mark back in May for the first time since 2014 — and input and labor costs tracking similarly — growers should be doing everything within their power to conserve energy and fuel heading into the 2022 growing season.

If you’re still using forced-air heating systems that have to warm up a giant volume of air from the ground all the way up to your greenhouse roof, Stuppy Greenhouses thinks its Hydronic Heat2O™ bench heating systems are a worthy structure upgrade that can provide immediate cost savings to your operation.

“Essentially, the system radiates heat on or under the bench and creates a sort of ‘heat envelope’ around the bench,” Michael Kovalycsik explains. “It’s ideal in propagation, as well as for growers that want to concentrate on heating the benches versus warming up the entire greenhouse.”

The concept is rather simple, and yet it’s innovative as well compared to traditional greenhouse heating systems. Growers can either run EPDM rubber tubes on the bench tops, or for higher heating output, install Stuppy’s all aluminum fin product underneath the bench. Depending on how many benches you are heating, the system can have a heat source as small as a standard home water heater unit, says the marketing manager and regional sales specialist. Naturally, for higher heating loads a boiler will be used for your heating source.

“It’s a simple closed-loop heating system, so there’s no need for you to refill or constantly monitor water levels,” he adds. “You can integrate it with a digital thermometer or most common greenhouse controllers, and it will basically run itself as needed depending on your desired soil temperature.”

Noting that in general any water heating system will be “much more efficient” than any of its forced-air counterparts, Kovalycsik suggests to growers that the Hydronic Heat2O system can save an operation 25% to 30% annually on its fuel consumption, even when fuel prices are in the affordable range. And Stuppy has designed the system to be completely DIY from an installation standpoint with no special tools required, so growers won’t necessarily have to hire installation crews.

“It’s energy efficient, designed for the grower to install, and offers total energy savings from the initial startup,” Kovalycsik says.

For more information on upgrading your heating system to Stuppy’s Hydronic Heat2O system, head over to bit.ly/StuppyHH. Most installs take place between October and December so growers are prepared to kick off early production between January and March.