Monday, 28 May 2007



Have you ever looked at the ingredients in fertilisers? If so you will be aware of the three numbers (often called NPK) on a fertilizer package that tell you the percentage of the primary nutrients’ makeup by weight. These percentages in fertiliser compounds are formulated for everything from asparagus to zinnias. The three main components are:

Nitrogen (symbol N) for leaf development and vivid green colour.

Phosphorous (symbol P) for root growth.

Potassium (symbol K) sometimes called potash, for root development and disease resistance.

I was asked about the percentages recently because they noticed that if a bag has a ratio of 16-4-8 NPK (16 percent nitrogen, 4 percent phosphorous and 8 percent potassium), this adds up to 28%. What, they wanted to know, is the other 72% made up of? Well you will be horrified to learn that to make up the weight the fertilisers are pumped full of bulking agents, usually inert filler material, such as clay pellets or granular limestone. These, the manufacturers say are to help us poor gardeners distribute the ingredients in an even fashion on the ground, in much the same way that sand is added to small seeds to get an even distribution. This doesn’t do much for the environment when you think that two thirds of the ingredients are waste products, shipped half way across the world using up loads of fuel. This fact might make us read the application rates on the back of the packets before it’s administered!


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