Beyond the Basics in the Garden: Macronutrients

Nutrients are necessary chemical compounds that are found in every living thing on the planet. They are required to break down food to supply energy to all organisms, including people, animals and plants. Plants rely mainly on sixteen elements for proper growth and development. Three of the elements the plants gather from the air; carbon, hydrogen and oxygen. The other thirteen come from the soil and can be broken out into two broad categories, macronutrients and micronutrients. This article will cover what macronutrients are, how the plant uses them and what deficiencies of each one tend to look like.

Healthy pea plants
Healthy pea starts

Macronutrients (sometimes called major nutrients) are heavily used by plants and are prone to being depleted rapidly without proper soil amendment. Macronutrients are broken out into two groups: primary nutrients and secondary nutrients. The three primary nutrients are nitrogen, phosphorus and potassium. It is these three elements that you will see in most commercial fertilizers. They are listed as NPK and shown as three numbers, 10-10-10 as an example. That means that it is 10% nitrogen, 10% phosphorus and 10% potassium in that particular fertilizer. The secondary nutrients are calcium, magnesium and sulfur. The primary and secondary nutrients are only differentiated by the quantity that a plant needs but not by importance.

Healthy lettuce starts
Healthy lettuce starts

Nitrogen (N)

Nitrogen promotes vegetative growth {the green parts above the ground; leaves, stems, etc.} and is the most widely used element in plant nutrition. It is readily lost from the soil due to leaching, erosion and being used up by plants. Nitrogen is vital to plants because it is a major component of chlorophyll. Think back to your grade school science class about photosynthesis: chlorophyll uses sunlight to produce sugars from water and carbon dioxide. Yellowing of older leaves can be the first sign that the plant is nitrogen deficient. Some crops like legumes {peas and beans} can be inoculated with certain bacteria to form a symbiotic relationship that converts nitrogen from the air into usable nitrogen for the plants. The process is called nitrogen fixation. Inoculants can be found at most stores that sell seeds or online.


Phosphorus (P)

Phosphorus is responsible for root growth, helps set buds, increases overall vitality and can increase seed size. It can also increase the nitrogen fixing capacity of legumes. Phosphorus is highly involved in the transfer of nutrients inside the plant and plays a vital roll in new cell development. Deficiencies of phosphorus can display as darkening of leaves, even to the point of turning slightly purple.

Phosphorus Deficiency
Darkening of leaves is a sign of phosphorus deficiency.Phosphorus Deficiency


Potassium (K)

Potassium affects the plant shape, as well as the color, size and taste of produce. Potassium plays a major role in the movement of nutrients, water and carbohydrates in the plant tissue. Just like nitrogen, potassium can easily be leached out of the soil. Deficiencies will first show as lightening in the leaf margins that can be light green to yellow. This can progress to browning and eventual the leaves will drop. The veins of the leaves may stay green while the rest of the leaf is turning yellow. If a plant is deficient in potassium it decreases it’s overall resistance to disease and pests and can leave the plant stunted and yields reduced.

Calcium (Ca)

Plants use calcium in large amounts mainly for the formation of cell membranes and cell walls. Because of this, calcium deficient produce will have a significantly reduced shelf life. Calcium displaces salts in the soil, which helps water penetrate into the ground. The availability of the calcium in the soil is affected by the soil’s pH. As a rule, pH levels of 7.5 to 8.3 will have more available calcium than any other pH range. Deficiencies will show up as premature death at the growing points, dropping of blossoms and buds, blossom end rot and bitter pit.


Magnesium (Mg)

Magnesium is naturaly released into the soil when certain types of rock minerals decompose. Just like the rest of the macronutrients, magnesium in vital to many of the plants’ functions. It’s most important function is as the central atom in the chlorophyll molecule. Magnesium is a mobile nutrient and deficiencies will show, first, in the older leaves. The leaves will turn yellow, while the veins stay green. High levels of magnesium can compete with the plants ability to uptake calcium and potassium.

Sulfur (S)

Sulfur plays an important role in many of the plants activities like the production of chlorophyll, and as a structural component of proteins, peptides and various enzymes. Sulfur also gives the characteristic flavors to garlic, mustard and onions, and plays a role in the ability of legumes to fix nitrogen in the soil. Sulfur is a fixed nutrient once inside the plant and deficiencies will show as lightening of the newer growth. The paleness can affect the whole plant but the older leaves will be darker then the newer ones. This is one way to tell the difference from nitrogen deficiency.


Uff da! If you are still with me after all of that, congratulations, you deserve a prize! {like big chunk of chocolate} I originally meant to cover both macro and micronutrients in one article, but as you can see it will be better served in two separate articles. So be on the lookout for the next installment of Beyond the Basics in the Garden.



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