How Plant Fertilizers Work

Understanding how plant fertilizers work begins with an understanding of the nutrients that plants need. And the focus of this short article is to cast a ray of light on plant fertilizers, which include both synthetic and organic fertilizers. Of course, there’s much more to gardening than simply plant nutrients and plant growth, but let’s begin with the basic science of how plant fertilizers work - both synthetic and organic. 

Every plant  - from a blade of grass to a towering oak tree - needs varying amounts of the three primary elements Nitrogen, Phosphorous, and Potassium, at different times during the plant’s life cycle. For optimum health, plants do require other secondary elements and trace minerals, but these three primary elements from the periodic table are the most important. Fertilizer labels display these three elements using their international symbols - N for Nitrogen, P for Phosphorous, and K for Potassium - along with a number that indicates the percentage of the fertilizer that’s made up of each element. For example, if a  fertilizer label reads 10-5-3 , ten percent of the bag’s contents is Nitrogen, five percent Phosphorous, and three percent is Potassium. These numbers, often listed along with an application rate on the label, are there to help you apply the right amount of fertilizer in your garden. 

Simply put, all fertilizers  - both chemical and organic - work by delivering N, P and K to plants, and these three primary elements can only be absorbed by plants after the elements have been broken down into molecular form. Synthetic fertilizers have been engineered to dissolve quickly into molecular form, and the accelerated plant growth induced by these fast-acting fertilizers is attractive to many commercial growers. After all, that next crop of plants doesn’t really know or care how it gets its supply of Nitrogen, Phosphorous, and Potassium. So why not get to harvest time faster, and with more profit? Plenty of commercial growers see it that way.

Organic fertilizers depend on microorganisms naturally present in the soil to break the product down into molecular form, and the pace of this microbial activity is contingent on the temperature of the soil. So, not surprisingly, livestock manures, bat guano, bone meal, blood meal, kelp, meal, alfalfa meal, etc. etc. etc., all take far longer to break down into molecular form than water-soluble synthetic fertilizers. So why would a grower use a fertilizer that works more slowly and may even cost more?

Here’s where difference between the two growing methods sharply diverges. While chemical fertilizers can churn out fast, shiny crop yields for a time, often that water-solubility that delivers nutrients in the blink of an eye, also means that those nutrients will just as rapidly leach out of the soil. And over time, this nutrient leaching process can leave behind high levels of salts in the soil. This frequently alters soil pH levels, making the soil less suitable for cultivation, or sometimes even completely sterile, and only restored with tremendous effort. Synthetic fertilizers can also harm or entirely destroy beneficial soil organisms like earth worms and soil microbes, but these organisms aren’t needed to convert synthetic fertilizer into molecular form, and therefore often play little or no role in the growth of a chemically fertilized crop.

Meanwhile, organic gardening places tremendous emphasis on the relationship that plants have with the many beneficial organisms that are naturally present in the soil. You might even say that these soil organisms, including earth worms and microbes, are everything to an organic gardener. After all, organically-grown plants would receive no nutrients without the presence of these essential organisms that break down organic fertilizer into molecular form. Now, it’s true that organically-grown crops do grow more slowly than those fueled by synthetic fertilizers. But consider that with the careful addition of organic material, including manures, humus, and compost, organic soil -  while under continuous cultivation - can actually become more fertile over time. 

Put simply, one method could eventually result in soil sterility while another could lead to improved soil fertility. That's quite a difference, and well worth your thoughtful consideration.

And, it's no secret where we fall on this topic - after all, we’re Microfarm Organic Gardens. Our focus is backyard edible gardening, where it’s hard to picture a grower in such a hurry that she would choose a synthetic fertilizer over an organic option for an edible garden planted to feed her family healthy produce. 

But commercial agriculture is another story, and far too vast a political topic to be explored in this short article. So, true to the title of this piece, we’ve briefly weighed the specifics of how fertilizers work - both chemical and organic. Interested in learning more? Hopefully so, and we’d be delighted if you used this text as a starting point for further research on the topic. Let prudence be your guide in learning about and using fertilizers. And remember; gardening without an understanding or appreciation of your soil, would be roughly equivalent to learning all about various medical drugs and remedies without first seeking any understanding of what the human body requires for optimum health.