FERTILISER LABELS

Photo: Fertilizer labels can be very confusing.

(Click on the title for a link the the Royal Horticultural Society website)

Ian
Could you tell me something about fertilizers as the labels always baffle me and I don’t know which ones to use on my garden. Thanks D.N. Letterkenny

Reply
The contents of fertiliser packaging can seem a little daunting at first glance, but labels explain the composition and nutrient content of the product, helping you to make a well-informed decision about initial purchase and subsequent application in the garden. Although I would like to say that I try not to use these chemicalson the garden even if the product claims not to pollute the soil. The pollution will probably have been created somewhere else!

Information clarity
Although the details are complicated, the result of legislation is that fertiliser labels all display the same basic information. This allows one garden-fertiliser packet to be compared with another and should show clearly what is being bought.

Current legislation
The composition, packaging and labelling of fertilisers is controlled by legislation. This may be either British or European; both differ slightly in their content, with EC regulations becoming more prevalent, but both are satisfactory.

Statutory declaration
Fertiliser packaging is required by law to include a number of details, including the following:
The prescribed name of the product content, such as ‘NPK Fertiliser’
The major nutrient contents, nitrogen (N), phosphorus (P) and potassium (K)

Forms in which the nitrogen content is present

Solubility of the phosphorus content: P and K are usually expressed as their oxide content, followed in brackets by the content of the element

Levels of secondary nutrients present such as magnesium (Mg) and other trace elements
Any pesticide content (lawn weed-and-feed products, for example) as well as a statutory declaration to comply with

pesticide legislation

The name and address of the manufacturer
The guaranteed weight of the product
An EC product declaration, if the product is EC approved

Usable ingredients
The useful part of fertilisers are the elements, such as nitrogen, phosphorus and potassium, rather than compounds such as phosphorus pentoxide and potassium oxide.

Growmore has a ratio of 7:7:7 for these materials, but is actually 7 percent nitrogen, 3.1 percent phosphorus and 5.8 percent potassium, or 7:3.1:5.8. Therefore it is a high-nitrogen feed, rather than the ‘balanced’ fertiliser commonly assumed. As garden soils are more likely to lack nitrogen than other elements, Growmore is deservedly popular, especially as a spring fertiliser.

Unlabelled products
Materials not covered by fertiliser regulations may be offered as plant foods, without stating their nutrient content. This may be variable due to the parent material (as with pelleted poultry manure) or there may be other purported benefits.

Exempt properties
Fertiliser quality - freedom from lumps, solubility and quality of ingredients - is not covered by the label information. Agricultural fertilisers for example may contain potassium chloride. This is cheaper than potassium sulphate, but some plants are sensitive to chloride content. However, the fertilisers sold to gardeners are almost always satisfactory in these respects.

Application guidelines
Manufacturers of garden fertilisers usually add comprehensive information to help gardeners get the best from their products. Major manufacturers will conduct tests and trials, but generic fertilisers such as superphosphate and Growmore have recommendations based on experience as well as field trials. Guidelines cannot cover every possibility and gardeners may have to use ‘trial and error’ to achieve the best results. If you feel that you can garden organically and without the need for spraying then that is what I would recommend.

Thanks to Guy Barter from the RHS for his help

horticultural, environmental