17 important plant nutrients from water, air, and soil to help them grow

three plants growing from a lump of soil

A lot of people focus on the food that you eat, and that is important, but the truth is that what you feed your plants is just as important. Like us, plants need a variety of nutrients to grow and thrive.

Plants receive most nutrients through the soil, so testing for key nutrients is a good idea to understand what nutrients you might want to supplement in the form of plant food or fertilizer.

Three main plant nutrients: NPK (nitrogen, phosphorus, potassium)

The acronym NPK is common amongst the gardening world as the three main plant nutrients. NPK stands for nitrogen, phosphorus, and potassium (which is represented by the letter K on the periodic table.


Nitrogen is a major component of a variety of vital parts and processes of plants. It makes up a large percentage of protoplasm, amino acids, and chlorophyll. Plants receive nitrogen through the soil, so if your soil is deficient in nitrogen it is a good idea to supplement with plant food that contains this vital nutrient.


Phosphorus is an important component of nucleic acids in plants including DNA, RNA, and phospholipids as well. Basically, it helps plants convert other nutrients into building blocks so that they can grow. Phosphorus is naturally found in soil, but if your soil is deficient you can supplement with store-bought fertilizers like bone meal, crab and shrimp waste, or mushroom compost.


Potassium is important for plants because it is necessary for enzymatic activity. Potassium helps in the formation of proteins and carbohydrates, moisture regulation, and photosynthesis. It also is important for the color and shape of the fruit, and fruit is best produced when your soil is rich in potassium.


Carbon is another vital nutrient for plants but is received from the air and water rather than the soil. During photosynthesis, plants convert carbon dioxide into carbohydrates from the air, which helps to store and transport the plant’s energy. 

Can plants be deficient in carbon?

If carbon is in the air, that means that testing the soil won’t give you insight into whether or not your plant receives enough carbon. So how can you tell?

Carbon deficiency may occur if you have a high concentration of plants growing close together indoors, with poor ventilation. It causes stunted growth, and your plants might not use up as much water and other nutrients as usual.

You can’t fertilize your plants with carbon, so what can you do if you suspect a carbon deficiency?

Ensuring your plants have enough ventilation or adding a fan to circulate the air can help if you think your plants are suffering for carbon deficiency.


Hydrogen helps in the plant’s production of sugars and plant material. Rather than being pulled from soil or the air, hydrogen is provided to plants mostly through the water. 


Wait a second — I thought plants produce oxygen!

It’s true, plants produce oxygen and glucose during photosynthesis! But they also require oxygen during the process of aerobic cellular respiration. Plants can experience oxygen deficiency at their roots if they have poor drainage or if they are overwatered. 

Oxygen deficiencies can be avoided by making sure your soil drains properly, and by watering less frequently once the soil has dried.


Magnesium is important for enzyme reactions in plants and is an important part of chlorophyll molecules. Plants get magnesium from the soil, and it is absorbed through the roots of the plant. Epsom salt is a common fertilizer that people use to increase the magnesium in the soil for their plants.


Sulfur is needed for amino acids, vitamins, and chloroplast, and is vital to the process of photosynthesis. Sulfur is added to the soil naturally as organic materials decay and can be supplemented by adding aged manure or compost.


Calcium is needed for the growth of leaves, and less so for fruit, seeds, and roots. It is an important component of cell walls and the process of cell division. In tomatoes, blossom end rot is a common symptom of insufficient calcium. The growth of your plant can also be stunted if it can’t get enough calcium from the soil.

Many people use crushed eggshells to add extra calcium to their soil. Especially when you are planting tomatoes, it can be helpful to add eggshells to the hole you are planting, underneath the root ball of your plant.  

Important micronutrients for plants:

Plants also need micronutrients (much like you and me!) These typically are needed in much smaller quantities.

Micronutrients plants need include:

  • Chlorine
  • Boron
  • Zinc
  • Manganese
  • Copper
  • Nickel
  • Iron
  • Molybdenum

Like humans, plants need nutrients for healthy growth. There are some nutrients that are needed in greater quantities, like nitrogen and calcium, and others that are needed only in trace amounts. It’s a good idea to get your soil tested to understand the nutrient balance so you can supplement with plant food and fertilizer for the healthiest plants possible.

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