As professional growers will appreciate, a lot of hard work goes into creating the environment that container nursery stock, perennials, pot plants and bedding plants require. Fortunately, controlled-release fertilisers (CRFs) offer a convenient way of helping them to achieve this aim by ensuring that their plants gain the right kind of nutrition at the right time.
While such useful products may seem like a fairy tale, they are in fact a very real result of applied science and innovative technology. Andrew Wilson is technical manager for ICL Specialty Fertilizers, which produces the established CRF brand Osmocote. He explains: "A CRF is a granule containing nitrogen, phosphorus and potassium (NPK) — and, depending on the product, they can also contain magnesium and other trace elements. These are then covered in a coating."
He notes that Osmocote features an organic, resin, semi-permeable coating. "As water penetrates through the coating it dissolves the nutrients inside the granule. The osmotic pressure inside the granule releases the dissolved nutrients through the coating. It sucks water in because it’s very concentrated inside and then, as the pressure builds up, it pushes out the fertiliser through the coating."
CRFs are also influenced by temperature. Wilson explains: "They are temperature-related. The only thing that affects the release of the fertiliser is the temperature. The warmer it gets, the more it releases. That’s the basics of it. It’s not affected by pH levels, salinity, water quality and rain."
Wilson adds that, when all the nutrients have been released, the resin coating breaks down gradually. Higher temperatures will speed up the nutrient release and therefore shorten the product’s longevity, while lower temperatures will slow down the release of nutrients and extend longevity. Cleverly, this means the plants are getting the nutrients they need for the conditions they are experiencing.
Osmocote: a finely-tuned product
ICL usefully offers the industry a range of different Osmocote products for ornamental crops of many shapes, sizes and species.
This year, the brand celebrates its 50th anniversary. Wilson says: "We are constantly developing our products and over the years we’ve constantly improved them. We have been making Osmocote since 1967 which was the first-generation product — a coated NPK granule. And then we produced a second-generation product, Osmocote."
Wilson explains that CRFs are calibrated products: "The thickness of the coating and the chosen ingredients reflect how fast the fertiliser will release. For example, a 3-4 month product will have a
thin coating, while a 12-14 month product will have a thicker coating. It’s the thickness of the coating that gives it the longevity." Osmocote products offer growers a choice of longevities. For example, Osmocote Pro includes NPK, magnesium and trace elements (the micronutrients that the plant requires in small amounts) and is available in several longevities, from 3-4 months up to 12-14 months.
Patterned release technology
While second-generation products such as Osmocote Pro have an efficient release of nutrients, ICL’s third- and fourth-generation products are even more finely tuned. The third-generation Osmocote Exact features patterned release technology, which gives a guaranteed release pattern due to its unique production process and extended quality control process. The steady and continuous nutrient release ensures crop safety and ensures nutrients are available exactly when the plant needs it.
Osmocote Exact with Double Coating Technology (DCT) is the fourth generation, featuring programmed nutrient release, when ICL can actually specify the release pattern that the grower needs. Understanding that a young plant’s nutrient demand is initially quite low after potting but much higher after establishment has led to the development of a unique Double Coating Technology (DCT).
These second coatings have a different composition to the original resin coating and they work by postponing the product’s start-up by up to three months (compared with Osmocote’s traditional release start-up of one or two weeks). Osmocote Exact Hi.End features, typically, 25 per cent DCT coated granules where a second coating delays nutrient release by six weeks up to three months depending on the longevity. This gives a release pattern that is initially lower but with a higher release later just when the plant’s nutrient demands are highest. This is one of ICL’s key products, and Osmocote Exact Hi.End grows the highest-quality plants by matching plant nutrient demand and minimising leaching of nutrients.
Postponing nutrient release
Moreover, further Osmocote Exact DCT development sees products such as Osmocote Exact Protect have a second coating added to 100 per cent of the prills, postponing the product’s start-up by up to three months. As such, product can be applied at potting stage in the winter months but will hardly release until the growing season has started, meaning that potential leaching and wastage is limited. "So it gets very technical," Wilson asserts.
Not surprisingly, the process of creating Osmocote is so specialist that "we have only got two factories in the world — one in Holland, one in the USA" Wilson reveals. "They each have several coating lines."
Admittedly it is fascinating to consider the journey that CRFs make — from a factory assembly line across the seas all the way into a plant pot — but if they help growers to produce colourful plants that delight their customers, it is arguably worth the effort.
- This is content produced in partnership with ICL. Read the full story of 50 years of Osmocote here.