Q: Fred, early this spring, I’d like to surface apply Osmocote® Blend 18-5-12 formulation to an overwintering house, but the bag label states:  “This product is not recommended for use in covered production areas or in propagation.”  Does this mean I can’t use this product as I intended?

--Bill, Nursery Grower, New York

A: Bill,

Before delving into this topic, let’s revisit the definition of “covered production area.” ICL Specialty Fertilizer defines them as: “Growing areas that are clad in plastic, glass, or other covering that trap heat and protect actively growing plants from unfavorable environmental conditions. May be actively heated (e.g. greenhouses) or passively heated by the sun (e.g. unheated hoop houses).”

ICL Specialty Fertilizer includes this type of information on the back of each fertilizer bag to help guide growers to use each product in the best possible way. If you read our product sheets or the back of any fertilizer bag—which we highly encourage growers to do before using the product—you will see a number of different statements and recommendations depending on specific formulations. I’ll explain a few of these statements here, dividing them up by the different Osmocote brands.

Osmocote® Plus and Osmocote® Labels:

 “For Professional Use Only. Recommended for use in greenhouse, nursery and foliage production, container gardens, interiorscapes and landscapes.”

These products are homogeneous, 100-percent coated and contain only nitrate and ammoniacal N. Therefore, there’s no chance that the nutrients will separate within the bag, ensuring growers uniform nutrient application across a wide range of uses. Since these products are 100-percent coated, they are considered safe for use in a variety of environmental conditions. That’s why ICL Specialty Fertilizers recommends them for all professional horticulture applications, including covered production areas.

Osmocote® Blend Labels:

“For Professional Use Only. Recommended for use on nursery stock, foliage and landscapes. This product is not recommended for use in covered production areas or in propagation.”

Generally speaking, Osmocote Blend fertilizers are blended, non-homogeneous and may contain slow-release nutrients. Some of them contain significant levels of urea N, while others do not. Because of these variations, Osmocote Blend products have been divided into distinct categories organized by where (e.g. outdoors, cool temps, protected structures) and for what purposes (e.g. quick green-up topdress) they should be used. Since these fertilizers are categorized in such a manner, it’s very important to read and follow the specific use recommendations for each product, as they definitely will vary from category to category. 

While they’re perfectly suitable for nursery and landscape use, ICL Specialty Fertilizers doesn’t recommend the Osmocote® formulations with high levels of urea N for use under cover since a grower could encounter production problems, such as excessive release of soluble salts during overwintering. This is even more of a risk for growers who do not closely monitor their crops and growing environments. Can they be used under cover? Yes, IF the grower exercises extreme care. That’s why ICL Specialty Fertilizer advises growers who want to use these particular Osmocote Blend formulations under cover to do due diligence beforehand to avoid this type of situation. If a grower is unable to monitor soluble salt levels, ventilate and/or adjust irrigation practices, ICL Specialty Fertilizer doesn’t recommend the use of those formulations under these circumstances. That said, there are many growers who use these formulations successfully in covered growing areas, but these growers have completed trials, made necessary adjustments to their growing practices and have initiated a monitoring program to ensure success.  Osmocote Blend 17-5-11 and 18-5-8 are recommended for indoor use.

I can’t emphasize strongly enough—before using any of these products, first read the label recommendations. If you need further assistance, don’t hesitate to contact your local ICL Specialty Fertilizer Territory Manager for help determining which product is most appropriate for your needs.

Osmocote Blend Topdress Labels:

“For Professional Use Only. Recommended for use on nursery stock, foliage and landscapes. This product is designed for topdress application only. Do not incorporate into growing media. Not for use in covered production areas or in propagation.”

These products are blended, non-homogeneous and may contain a significant amount of uncoated nutrients for rapid green-up of crops. ICL Specialty Fertilizer Topdress products are definitely not designed for use in covered production areas, and they should not be used in that situation.

Before making changes to any fertilizer program (e.g. formulation, rates, crops or growing systems), growers should perform a product trial to adequately assess the impact of any program change before making a wholesale switch. Product selections and application rates should always be based on individual grower practices. 

If you have any questions about the suitable use of any ICL Specialty Fertilizer formulation, contact your local ICL Specialty Fertilizer Territory Manager.

Have a question for Dr. Hulme? Simply e-mail it to [email protected].