Focus on fertilizers

For many years, manufacturers and providers of greenhouse and nursery fertilizers have been striving to develop new technologies that can help growers achieve better crop quality with fewer inputs and less expense. Although there are many established brands that have been successful in the marketplace, it’s necessary to continuously improve technologies to meet current crops, growing systems and ever-changing market conditions.

According to Dr. Roland Leatherwood, senior scientist at Everris’s North American headquarters, access to new technologies and processes is key to a better future for both growers and the companies that supply them.

“There are some production problems that greenhouse growers have experienced for years,” Dr. Leatherwood says. “While growers and suppliers have come up with some solutions to these problems, the solutions themselves often don’t fit well in many situations.”

Irrigation water woes
If not treated, high alkaline (or high bicarbonates) in irrigation water can build up over time, leading to rising root zone pH levels, especially in plugs and longer-term crops. As media pH’s rise too high, micronutrient levels (especially iron) are limited. The younger foliage of many crops will respond to this nutrient deficiency by losing green color, making them unattractive and less saleable.

Historically, growers have had two options to solve this problem. The first solution included reducing irrigation water’s high alkalinity by injecting mineral acids like sulfuric or phosphoric acid. While this is a highly effective solution, it requires extra costs and special equipment, and it exposes workers to potentially hazardous material when mixing and storing mineral acids. This solution also requires constant monitoring to ensure the correct amount of acid is being added at all times. Because of these issues, many growers do not choose to acidify their irrigation water; rather, they manage the consequences of high root zone pH in a different manner.

In the second solution, growers can treat the symptoms of the problem by making proactive or prescriptive applications of micronutrient supplements such as chelated iron sprays or drenches. This can be a workable option, as all crop types do not react the same way to high media pH. However, like the previous solution, it also requires growers to incur extra fertilizer costs and crop monitoring to ensure that applications are timely and efficacious.

“Some growers use crop-specific formulations that contain higher levels of micronutrients, but this can create an issue if a variety of crops with different nutrient requirements are being grown simultaneously in the same space,” says Chris Buchheit, Everris’s regional marketing manager for ornamental horticulture fertilizers. “For example, a high-iron formulation can solve an iron deficiency problem in one crop while causing iron toxicity in another iron-sensitive crop nearby. If a grower decides to delay treatment until chlorotic symptoms are already present, it may be too late to fully reverse the visual symptoms, and the economic value of the crop may suffer.”

The most ideal solution to this production problem would be to remedy the high alkalinity irrigation water without having to mix in mineral acids. An acidifying component designed as a safe alternative to conventional liquid acids is allowing growers to fight increases in growing media pH levels while simultaneously feeding plants.

“When mixed in a concentrate tank, these fertilizers will create some active acidity that will continuously take out a portion of the irrigation water alkalinity, helping to keep root zone pH down,” Dr. Leatherwood explains. “While there are of course limits to the active acidity, these products can reduce or eliminate a growers’ need to acidify irrigation water and also reduce their need for supplemental micronutrient applications due to high growing media pH.”

Fertilizer shortfalls
Traditionally, greenhouse growers have used water-soluble fertilizers as their main source of nutrients. These products are dissolved in water and drenched into the growing media, providing an immediately available dose of nutrients to the crop.

While water-soluble fertilizers offer great flexibility, the effects of a single application do not persist for very long in the root zone. Furthermore, when applying water-soluble fertilizers via overhead application methods, many of the nutrients can be lost in wasteful runoff if the irrigation water isn’t captured and recycled.

“Additionally, once crops leave the greenhouse, the grower’s ability to supply those plants with nutrients is disrupted or totally abandoned,” Buchheit says. “This can cause a crop’s appearance to suffer in the post-production process, lowering the crop’s value and decreasing potential profits.”

To overcome this problem, some growers combine the use of controlled-release fertilizers with the use of water-soluble fertilizers during the production phase. Or they choose to surface-apply a dose of controlled-release fertilizer onto crops on their way to the garden center. When a controlled-release fertilizer is applied at a low rate to these typically small pots, however, it’s often difficult for growers to distribute the fertilizer prills evenly.

Because most controlled-release fertilizer labels are designed for the container nursery industry, greenhouse growers often select the incorrect products for their growing conditions. In other words, they choose a product with the wrong longevity, nutrient components and release patterns and — worst of all — excessive rates.

To overcome the problem of uneven controlled-release fertilizer applications within small greenhouse pots, new technology involves a much smaller prill designed especially for greenhouse production. This controlled-release fertilizer is 100 percent coated and supplies a full array of essential elements in a ratio suitable for many color crops. This product should be incorporated into the growing media prior to planting and used as the sole source of nutrients, Dr. Leatherwood says. Even better, it should be incorporated in combination with water-soluble fertilizer to tone plants.

Dr. Fred Hulme is director of technical services at Everris. Contact him at fred.hulme@everris.us.com.