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What is in a plant's diet? (3/4): The many, many micronutrients

So, we’ve already reviewed every major ingredient of what that plants ‘eat’ (see our first article in this series to know why this term is technically incorrect), and only the micronutrients remain. If you think that the ‘micro’ part relates to less importance as well as to less plant uptake of these elements, though, that’s not right at all! Micronutrients may be small in percentage of all that a plant eats, that’s true (they comprise only 1% of plant tissue, according to this extremely useful 2006 FAO report, which we mentioned in the second article of this series), but micronutrients are also essential for a plant’s wellbeing. They are like the pea in that Hans Christian Andersen fairy tale, which kept the princess awake even though it was under twenty quilts and twenty mattresses: a deficiency of micronutrients in your plants can keep you awake at night as well, wondering what’s wrong with a soil that has perfect NPK levels. To finish this brief series of articles on plant nutrition, here we present to you the seven essential micronutrients that comprise that last, tricky 1% of your plants’ diets:

  • Zinc (Zn) is useful to the plant in the production of several enzymes and proteins, and plays an essential support role in the production of seeds and the number of mature fruits that a plant ends up yielding.
  • Molybdenum (Mo) serves a basic role in the process of production of proteins, which in turn the plant uses to build new tissue. It also has a less well-known but definitely present role in how legumes fixate nitrogen (N) in the soil, with molybdenum deficiencies correlating with a reduction in their capability to do so.
  • Manganese (Ma) is fundamental in the process through which the leaves of the plant perform photosynthesis. To get a little bit more complex, we can explain it thus: in photosynthesis, the plant takes six molecules of CO2 and six molecules of water. These are broken down and recombined to make one molecule of glucose (which the plant eats) and six molecules of oxygen as a byproduct, which the plant releases (and we breathe!). Manganese atoms, with one atom of calcium, form a complex (a sort of little demolition claw) which breaks down water molecules that enter in contact with the cell, allowing photosynthesis to begin.
  • Iron (Fe) does a little bit of everything, but its main purpose is to help the plant synthetize chlorophyll, without which it cannot perform photosynthesis. As if that alone wouldn’t suffice, it also helps it to assimilate nitrogen, produce carbohydrates and breathe!
  • Copper (Cu) is another essential, photosynthesis-dependent element. Around 70% of all the copper in a plant is present in the chlorophyll molecules, where it fulfills a basic role in transferring electrons that are ‘excited’ by sunlight, so to say, deeper into plant tissue where they are converted into energy (after a very much more complex process, but let’s not get into that for now).
  • Chlorine (Cl) plays a part in the processes of hydration of the cell, and in keeping tight its balance against the external environment, so to say (what scientists call ‘osmotic pressure’). Chlorine might seem like something that people place in their pools to kill algae, but its deficiency actually makes plants wilt and die.
  • And, finally, Boron (B) is, according to the aforementioned FAO report: “like the mortar in a brick wall, the bricks being the cells of growing parts such as tips… Key roles of B relate to: (i) membrane integrity and cell-wall development, which affect permeability, cell division and extension; and (ii) pollen tube growth, which affects seed/fruit set and, hence, yield.”

All of this having been said, the last question is: how to ensure that all micronutrients and macronutrients are present in the soil, in the necessary quantities, and without bombarding it in such a way that most of it gets washed away or that it’s too much and kills your plants? Well, that is an issue for our last article in this series. Happy growing!

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