Three Secondary Nutrients Walk Into a Garden

By Cory Hughes
Published: February 5, 2015 | Last updated: January 29, 2019 05:12:01
Key Takeaways

While everyone is out there searching for a magic bean, some secret ingredient that will mysteriously triple their yields, the truth is that all you need are the basics. Understanding the basics of horticulture and knowing how much of what nutrients your plants need to grow and be healthy is a must-have skill for anyone aspiring to have a green thumb.

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Nutrients are a fundamental part of growing. They are the fine cuisine of the horticulture world. Combine them with sunlight, CO2 and a spoonful of love, and your plants will spring to life.


Plants require 16 elements to live strong, healthy lives. These nutrients are broken into three categories: primary macronutrients, secondary nutrients, and last and I guess technically least, micronutrients.

When it comes to your primary macronutrients, nitrogen, phosphorus and potassium are the major players that are required in the greatest volumes, but that’s not what we will be discussing here today.


Today I’d like to stress the importance of the secondary nutrients: calcium, magnesium and sulfur.

For the most part, your plants will thrive if you simply use one of the many pre-formulated nutrient mixes from off the shelf at your local grow shop, but it is a good idea to understand how each nutrient affects your plants to determine if the mix you are using is really working.


Plants require less of the secondary nutrients than they do the primary macronutrients; however, their role in the health of the plants is no less important.


Calcium for Plants

The first of the secondary nutrients on the list is calcium—a plant growth regulator with many roles.

Calcium assists with cell division and the formation of new plant cells. It aids in photosynthesis and it helps plants take in other nutrients. Even though it is a secondary nutrient and absorbed much more slowly that the primary macronutrients, it can be found in fairly high concentrations throughout most plants.

Calcium is also an essential element found in the structure of plant cell walls. There are several factors that can affect your plant’s ability to absorb calcium and may result in a calcium deficiency.

A calcium deficiency can be spotted by curling of leaves, stunted growth of fruits and damage to roots. Since calcium is a necessary component of cell walls, a deficiency can be expressed as a decaying of the surface plant matter.

Another sign your plants may be calcium-deprived is if your soil pH is overly high. If your soil or medium’s pH is high, it may mean that calcium has bonded with other nutrients, becoming unavailable for absorption.

This can be fixed by incorporating a calcium acetate or calcium magnesium formula into your feed schedule.

Magnesium for Plants

Next up is magnesium. Magnesium is a core element of chlorophyll, the key component in photosynthesis.

Chlorophyll is essential for all plant life. It is a photoreceptor, which means it takes in light and uses it to synthesize carbohydrates. When a plant is magnesium-starved, you will start to see a yellowing of the leaves between the veins.

This is due to a breakdown of chlorophyll, which is what is responsible for a plant’s natural green color.

As the leaves of a tree naturally change colors during autumn, the chlorophyll in the leaves is breaking down. This is what we have to thank for the beautiful September views we are accustomed to seeing as the weather begins to cool.

The most common cause of magnesium deficiency in home gardens is a lack of proper magnesium fertilization.

Sulfur for Plants

The last of the secondary nutrients is sulfur. Sulfur is another essential element that some would consider the fourth macronutrient. Its purpose is to aid in the creation of amino acids, the foundations of proteins.

It is also necessary for the creation of chlorophyll. Much like other deficiencies, the first signs can be spotted by a yellowing of the leaves. Once again this is due to a breakdown in chlorophyll formation, resulting in the change in color.

A sulfur deficiency can also result in the plant’s stunted growth. Sulfur deficiencies do cause different changes in color in varying plant species, as more than just green plants require it. The most common changes are a paling in color that may occur smoothly or in spots.

Sulfur isn’t simply absorbed by plants. It has to undergo a mineralization process as a result of microbial activity.

Once converted to sulfate, it becomes available for plants to take in. Dealing with a sulfur deficiency is tricky as it is easily confused with other deficiencies, like nitrogen. Often people treat their soil before getting started to ensure a deficiency is avoided.

Understanding the basics of your nutrients is essential in identifying problems with your plants. While identifying issues with your garden can be challenging, do not fear, there are lots of products and tons of information available to assist you on your quest.

The best way to avoid deficiencies is to get to know your plants, your strains and your environment, and educate yourself on the best ways to ensure adequate fertilization of your crop.


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Written by Cory Hughes | Commercial Grower

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Cory Hughes is a former police officer turned full-time commercial grower in Denver, Colorado.

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