The Chemistry of Plants

Taming the numbers on a fertilizer package. Not easy. Yet there are only three of them. And in the end, all we want is to make our plants happy.  

N-P-K, the Main Trio

On most fertilizer packages, there are three numbers, separated by a dash. Always in the same order, N-P-K, they designate three chemical elements. N for nitrogen, P for phosphorus and K for potassium. Each number designates the percentage of this element contained in the package. For example, a fertilizer with a formulation of 10-5-6 indicates that there is 10% nitrogen, 5% phosphorus pentoxide (P₂O₅) and 6% potassium oxide (K₂O), therefore in total 21% of fertilizer units.

With this information, one would think that choosing a fertilizer with high numbers would result in a more effective fertilizer. Well, no. First, because plants have a certain limit to their capacity to absorb these elements. It is useless to give three cups of nitrogen to a plant that only needs a tablespoon. Everything else is leached away, that is, wasted. Secondly, while nitrogen, phosphorus, and potassium play important roles in plant growth and development, there are many other chemical elements that are just as important and that are naturally more present in organic fertilizers than in synthetic ones.

What Are Plants Made Of?

First and foremost, a plant is “CHO”. About 80% of a plant is water (H2O). Therefore, oxygen (O) and hydrogen (H) dominate, but also carbon (C), which is the essential material for all the elements that make up plant tissues. Plants obtain these three elements from the air (CO2 and O2) and, of course, from water.

Then, arrives the famous trio, N-P-K, present in large quantities in all plant parts. Nitrogen, for example, is an essential component of the chlorophyll molecule. Cell membranes are made of phosphorus and potassium is useful for ensuring the free circulation of water and nutrients. Reductively, it is often said that nitrogen is for leaves, phosphorus for flowers and fruits and potassium for resistance to cold and disease. Let’s just say that the roles played by each element are much more diverse and complex. But we’ll save that for advanced biochemistry!

Most plants meet all their needs with about fifty different chemical elements. The most important are the major elements and those of secondary order are called the minor elements.  

The Major Leagues

In addition to the 6 elements mentioned above, there are three others that are very important, sulfur (S), calcium (Ca) and magnesium (Mg). These are the essential ones, present in greater quantities in plants.  

Minor Leagues

Micronutrients, or trace elements, are present in smaller quantities, sometimes even in infinitesimal quantities, but they are still very important. These include iron (Fe), manganese (Mn), copper (Cu), zinc (Zn), molybdenum (Mo), boron (B) and chlorine (Cl). Even if their presence is not always indicated on the packaging, they are indeed present in natural fertilizers. In fact, this is what often distinguishes a synthetic fertilizer from a natural fertilizer: those little extras.

Many scientists agree to recognize the superior efficiency of organic (or natural) fertilizers, even if the numbers of the N-P-K ratio are lower than those of synthetic fertilizers. Natural fertilizing elements are better protected from leaching, they experience a better synergy with other micronutrients in the soil and above all, they stimulate the biological activity of the soil. It must therefore be emphasized that plant nutrition does not only depend on fertilizers. It is also influenced by the richness, texture and structure of the soil, its microbial life and its humidity level.  

The moral of the story is that you need to provide your plants with the most complete range of chemical elements possible, in order to ensure that the plant meets all of its needs. The plant, through its roots and a little through its leaves, absorbs the elements it needs. Yes, it chooses. And each plant has its preferences. Corn, like many grasses, loves nitrogen, tomatoes like calcium and magnesium, and so on. To avoid waste and unnecessary fertilization, the secret is to follow the manufacturer’s recommendations. Never double doses and respect the application frequencies. This way, you can be sure to use the fertilizers optimally and make your plants happy!