Using water-driven injectors and fertigation systems for greenhouse production

Exclusives from Urban Ag News

Originally published in Issue 11

Growers who incorporate water-driven injectors into their production systems are usually looking for simplicity and flexibility.

Whether fertilizing greenhouse ornamental or vegetable crops, many growers use an injector to take up fertilizer concentrate and mix it with water and apply it to the plants.

“From an application standpoint the same type of information related to water flow, pressure and dilution rate is going to be used whether a grower is producing ornamentals or vegetables,” said Chris Lundgren, national sales manager for horticulture at Dosatron International Inc. “The difference with greenhouse vegetable production compared to traditional bedding plant production is sometimes vegetable growers want more flexibility in their control over the rates of nitrogen, phosphorus and potassium. In vegetable operations, growers sometimes operate multiple injector units in line or in series. There is a tank A, a tank B and a tank for a diluted acid or some other supplement like a calcium-magnesium product that provides them with more control.

“The traditional bedding plant grower may be using a bag of 20-10-20 or 17-5-17, mixing the fertilizer and using one injector to deliver it to the whole production facility in a constant liquid feed program. In the vegetable greenhouse, the grower is looking for more variable control.”

Lundgren said as vegetable crops like tomato and cucumber go from the vegetative stage to the flowering and fruiting stages that most growers are going to want to have more control over how much nitrogen, phosphorus and potassium and any other supplements are going to be provided to the plants. He said this is the major difference between fertigation of traditional greenhouse/nursery crops and greenhouse vegetable production.

Photo courtesy of Dosatron International Inc.

Adding edibles to the product mix

Lundgren said ornamental plant growers who want to try their hand at producing edibles usually start with crops like lettuce, leafy greens and microgreens.

“The crop turnaround time is quick,” he said. “It’s a onetime harvest and the crop doesn’t have to be held for very long. The grower is trying to harvest as much off of one plant as possible. This is the quickest, easiest way to go from flowers to food.”

Lundgren said for crops like leafy greens only one fertilizer solution is usually needed because growers are trying to keep the plants vegetative.

“Because of the way these crops are produced, growers can get away with the same single bag fertilizer program that they are using to grow bedding plants,” he said. One change that Lundgren has seen bedding plant growers make when adding edible crops is to install some type of water treatment system.

“Bedding plants growers who are adding short-term crops like leafy greens have to be sure they are successful with those crops from the start,” he said. “Bedding plant growers are installing hydroponic production systems like nutrient film technique because that is going to be the quickest way to turn around these crops. The growers are being advised that water treatment is an important part of an edible crop program because the water is now being used as part of or as the substrate. This means the water’s contaminants are much more highly concentrated in the root zone compared to a soilless medium that is used for bedding plants.” Lundgren said growing poinsettias, tomatoes, cucumbers and peppers, are similar in that they are long-term crops.

“Typically for poinsettia, it’s a six month crop from stick date to out the door,” he said. “Six months of pest control monitoring and the IPM program has to be pretty much spot on as well as the plants having to ship on time. Tomatoes are more like a poinsettia crop.

“With long term crops, growers have more flexibility to make changes to rectify issues that occur. With a quick crop like leafy greens, a grower doesn’t have as much flexibility to fix mistakes.”

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An intimate, hands-on relationship

Lundgren said growers who incorporate water-driven injectors like Dosatrons into their production systems are usually looking for simplicity and flexibility.“Growers who are using Dosatrons tend to be more of hands-on growers,” he said. “The injectors become an integral part of how growers are doing things. Because these injectors are mechanical, growers have to physically make adjustments to change the ratios. There is an intimate relationship that happens between something mechanical, even though it is automating the process, and the users. That, in and of itself, becomes a reason why people are so attached to their injectors.”

Lundgren said proper maintenance can go a long way in extending the lifespan of the injectors. Some growers are operating injectors that are 15-20 years old.

“Water-driven injectors are mechanical devices and need maintenance just like a car,” he said.

“The harder an injector is run the quicker it has to be serviced. Those that are used to apply the same product all the time and aren’t used frequently don’t need maintenance as often. The longer injectors are operated, the harsher the chemicals that are run through them, and the more chemical diversity injectors are exposed to, the more frequently maintenance will be needed.

Injectors are used to apply everything from fertilizers, PGRs, sanitizers, insecticides and fungicides.”

Water treatment is an important part of an edible crop program because the water is used as part of or as the substrate. The water’s contaminants are much more highly concentrated in the root zone compared to a soilless medium that is used for ornamental crops.

Level of control

Lundgren said fully-automated environmental control systems that incorporate chemical injection usually require someone with technical expertise to do maintenance or repairs because of the complexity of these systems.

“Some growers desire more control and prefer using injectors,” he said. “Typically the growers who use injectors are out in the greenhouse manually testing the EC (electrical conductivity) and pH. Other growers need something that is not as mechanical that is tied in more to an automated environmental control system. These automated systems give them the capacity to make changes on the fly, using a phone or a computer. These systems are going to typically be provided by the environmental control companies.”

Lundgren said many of the large greenhouse vegetable operations have so much diversity that they need to rely on an automated system that is going to do a large capacity and be centralized.

“These growers are not going to want a lot of Dosatron stations throughout their facilities,” he said. “They don’t want to have to make mechanical adjustments in every pump house. It is much more sensible to use a fully integrated system in these operations. They might use some mechanical injectors for certain applications.”

Lundgren said fully integrated, automated environmental control systems have the ability to monitor the system and the plants, as long as the system is maintained. These systems can provide a lot of data including pH, EC, temperature and relative humidity.

“One of the greatest pros with fully integrated systems is growers can sit at home and monitor the greenhouses from their smart phones knowing that the fertigation program is spot on,” he said. “That definitely is an advantage.

“The discussion for growers using any type of fertigation technology comes down to: what makes sense for their operation and what makes sense for their business plan? Secondly, what level of technology are they ready for? If growers are more mechanical in nature and go out and monitor their crops daily, injectors probably better fit their production system. If they are a grower who wants an automated streamlined production facility and prefers working on a computer, then a fully integrated control system is likely a better choice.”


For more: Dosatron International Inc.; (800) 523-8499;;

David Kuack is a freelance technical writer in Fort Worth, Texas;

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