More isn’t Better: Organic Fertilizer Myths Busted

Posted by Katie Elzer-Peters
May 29th, 2009
Filed in Soil and Fertilizer
Tags: Compost, fertilizer, Soil and Fertilizer, synthetic, vegetables

Organic fertilizer

With the rabid interest in organic vegetable gardening reaching a fever pitch, questions about the amount and timing of fertilizer applications are bound to appear.  Wait – I sound like I’m writing a really bland paper to be delivered at a government conference.  Let’s start over.

Don’t you love that show Myth Busters?  I do.  They save me from trying out all of the ridiculous (stupid?) experiences that float around as “adventure” stories, or “self-help” ideas  (a recent repeat show saw the two main guys testing “sobering up” myths).  Well, today, I have put on my official “Organic Gardening Myth Busting Cap” (viking helmet?) to bust some myths about using organic fertilizer.

Myth 1: More is Better, in terms of Fertilizer

NOPE! Nothing could be further from the truth!  We frequently talk about the fact that putting extra fertilizer (synthetic or organic, in quick release form) in the garden is like watching your money float down the drain.  The practical matter is that soil can only hold on to a certain amount of nutrients at one time.  Once the soil is saturated with nutrients, any additional nutrients just leach out into the groundwater.  (Kind of like those commercials imploring people not to take vitamin supplements, because the vitamins end up, literally, down the toilet.)  However, there is another reason that more is not better in terms of organic fertilizer (or any fertilizer, for that matter).

You might think that if something is organic, you can’t have too much of a good thing.  Not so.  Too much Nitrogen in the soil leads plants to produce lots of weak plant growth, making them more susceptible to diseases and pests, which is likely to lead to frustration for organic gardeners trying to control pest and disease problems.

Myth 2:  Higher NPK Numbers mean More Growth

This is related to Myth 1.  The N-P-K number on a fertilizer is called “The Fertilizer Analysis.”  These numbers tell you how much Nitrogen, Phosphorous and Potassium are in the fertilizer, in relation to each other, and in terms of “active ingredient” in the package of fertilizer.  A 10-10-10 fertilizer has equal parts N, P and K.  It also has 30% active ingredients by weight or volume, and 70% fillers.

So, some people think that because organic fertilizers have lower analysis numbers, say 2-4-2 or 4-0-0, they need to use more of the organic fertilizer.  If they have to use more, that costs more money, which makes them want to use synthetics.

BUSTED! There are actually very complicated activities going on in the soil, most of which we haven’t even come close to understanding.  What we do understand, thanks to research conducted and reported by The Organic Center, is that vegetables grown with sustainable, organic methods have many times the amount of nutrients, beneficial phyto-chemicals and antioxidants that vegetables grown with synthetic agricultural practices.

Furthermore, while the vegetables grown with synthetic chemicals may, in some cases, be larger, their nutrient content is diluted, meaning you have to eat two or three times the volume of vegetables to get the same amount of nutrients from organically-grown food.

How can this be?  Lower fertilizer analysis numbers = better results?

It is the complex interaction of nutrients in various forms with insects, soil life, plants, and soil particles. We don’t really understand yet how it works, but it works.  So, organic gardening is NOT more expensive than conventional gardening, in terms of fertilizer.

Myth 3:  My Plant Leaves are Purple-I must add Fertilizer!

SORRY! Before you add any fertilizer, check the pH of the soil.  There might be plenty of nutrients in the soil, but they are not in forms available to the plants.  Each plant nutrient can exist in several different forms or molecular compounds.  The pH of the soil affects how tightly the nutrients bind to soil particles, and, conversely, how easy it is for plants to extract the nutrients from the soil and absorb them.  If your pH is off, adding more nutrients isn’t going to help anything, except make your wallet lighter.

Hopefully, you have a better picture of organic fertilizer, and will feel confident using organic fertilizers in your garden!