Reflecting on the impact that controlled release fertilisers (CRFs) have had on the UK’s commercial growing industry, horticultural consultant John Adlam recalls that: "We were introduced to CRFs in the 1960s. At that time there was a very cautious uptake by growers of the concept of controlled release. It was quite a departure from what they were familiar with and it probably took ten years before they were accepting of it. But they meant that the grower didn’t have to liquid feed. Considering everything else that they had to do on the nursery there were some labour-saving concepts that came with CRFs."
Adlam, a council member of the Horticultural Trades Association, also notes that using CRFs considerably reduced the release of nutrients into the environment. "The risks of ground water and surface water contamination are much lower." He adds that CRFs have also provided the UK’s horticulture industry with good nutrition in its growing media, particularly throughout the transition from peat-based to reduced-peat mixes.
Interestingly, Adlam recalls how working with CRFs was at first a bit of a learning curve for growers. "Early work carried out at the Efford Horticultural Research Station in Hampshire was very useful in helping growers to identify which products suited their requirements and how to utilise them effectively. There was also an interesting public dimension to it – people weren’t aware of what they were. I can remember having people ring me to say: ‘I have found these little balls in my soil. I think they might be slug eggs.’"
Adlam notes how further research carried out at the Glasshouse Crops Research Station in West Sussex in the 1970s, and in Efford in the 1970s and early 1980s, continued to give growers a good understanding of, and confidence in using, the products.
He also observes that, decades after CRFs were introduced to the market, the way in which CRFs are applied remains a subject of debate. Adlam advocates the use of the dibbling method – as opposed to having CRFs pre-mixed into the growing media. He opines that this method avoids the risk of making mistakes – such as accidentally putting the wrong growing media in the pot during a changeover period. "You can ‘add it to taste.’ I personally feel that this is something we should consider a lot more seriously because of the flexibility it gives you in the application of the CRF. If, for example, a grower pots small quantities of a large [number of] species, the dibbling allows you to adjust the CRF application accordingly." He also notes that the period between mixing CRFs into the growing media and potting a batch up "has got a use-by date." He adds: "Certainly, with CRFs you should not purchase products that you cannot use within three weeks of delivery."
Nowadays, notes Adlam, there are "a wide range of CRF products available from many different countries." He says: "We would all consider Osmocote to be the leading brand. Having said that, other products are not to be ignored." He concludes by noting that the EU’s current revision of its fertiliser legislation, which requires the CRF coating to biodegrade after two years, has left "some degree of a question mark hanging over the long-term future of these products." He adds: "It will be interesting to see what they will look like and how they will work in future."