In the good old days, people just put manure on their garden and things grew well. Keep in mind that manure was easy to come by before the advent of the car. The invention of fertiliser created a problem for manufacturers because they didn’t know which formulation they should use. Marketing solved the problem by creating the concept of a balanced fertiliser. This seemed to make a lot of sense. It was known that plants used nitrogen (N), phosphorus (P) and potassium (K), so why not provide them in equal amounts?
Bags of balanced fertiliser labeled with 5-5-5 or 10-10-10 became very popular with home gardeners. You could not go wrong since you were providing all three of the main nutrients.
After a few years, competitive companies wanted to get in on the action, and they needed a different marketing plan in order to compete. They asked the question, do plants really need the nutrients in equal amounts? In an attempt to answer this question, scientists measured the nutrient content of plants. It turns out that they don’t contain equal amounts of N, P and K. If they don’t contain equal amounts of nutrients, it does not make sense to use a balanced fertiliser, so companies started to sell different formulations based on plant type. Even though there is no good reason to use a balanced fertiliser, they are still highly recommended and very popular.
A balanced fertiliser is almost never the right choice because plants don’t use the nutrients in a balanced way and soil is rarely missing nutrients in equal amounts.
When you fertilise, add the nutrients missing from the soil. Don’t listen to expert gardeners or fertiliser manufacturers that make recommendations.
In most cases, soil does not need more phosphorus, so keep the middle number as low as possible.
Fertilizer Nonsense: Balanced Fertilizer; http://www.gardenmyths.com/fertilizer-nonsense-balanced-fertilizer/
Written by Robert Pavlis, author of three books, , Garden Myths , Soil Science for Gardeners and Building Natural Ponds.
This article is Myth #28 from Garden Myths: Book 1, available in the UK online from Amazon here: https://www.amazon.co.uk/Garden-Myths-Mr-Robert-Pavlis/dp/1542465222/ref=sr_1_1?dchild=1&keywords=garden+myths&qid=1605707945&sr=8-1
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