Plants get all the carbon, hydrogen, and oxygen they need from carbon dioxide and water, which they use to build carbohydrates during photosynthesis. To build other kinds of molecules they also need elements like nitrogen, phosphorous, and sulfur. Plants get these as well as other elements from the soil.

Just like you do, plants build their cells from carbohydrates, proteins, lipids, and nucleic acids. The difference between you and a plant is that you get all these molecules from your food, but plants need to build them for themselves.

Many elements exist as dissolved minerals in the soil. When plants absorb water through their roots, they also absorb minerals that act as both macronutrients and micronutrients. Macronutrients help with molecule construction, and micronutrients act as partners for enzymes and other proteins to help them function. Plants generally require large amounts of macronutrients and smaller amounts of micronutrients. The table lists the specific macronutrients and micronutrients plants absorb from soil.

The Essential Elements Plants Pull from Soil
Macronutrients Micronutrients
Calcium (Ca) Boron (B)
Magnesium (Mg) Chloride (Cl)
Nitrogen (N) Copper (Cu)
Phosphorous (P) Iron (Fe)
Potassium (K) Manganese (Mn)
Sulfur (S) Molybdenum (Mb)
Zinc (Zn)

You can remember the most important elements for plants with the phrase C. Hopkins Café, Mighty Good. The CHOPKNS CaFe Mg stands for carbon, hydrogen, oxygen, phosphorous, potassium, nitrogen, sulfur, calcium, iron, and magnesium. All these elements are macronutrients for plants, with the exception of iron, which is considered a micronutrient.

If plants don’t get enough of one of these important elements, they can’t function correctly. Without carbon, hydrogen, and oxygen (from carbon dioxide and water), plants can’t grow at all. And even though plants need smaller amounts of other elements, each missing element causes a specific problem.

Test your understanding of plant nutrition with the following questions.

For numbers 1-5, use the following terms to identify whether the nutrient is a macronutrient or a micronutrient.

a. Macronutrient

b. Micronutrient

  1. A plant gets sulfur from sulfate (SO4) in the soil.

  2. A plant takes in calcium as calcium salts from the soil.

  3. A plant takes in nitrogen as nitrates (NO32) from the soil.

  4. A plant takes in magnesium (Mg) from the soil.

  5. A plant absorbs copper (Cu) from the soil.

  6. True or false: Plants get carbon from the soil.

  7. True or false: A plant’s weight comes mostly from the minerals it takes from the soil.

The following are the answers to the practice questions:

  1. The answer is a. Macronutrient.

  2. The answer is a. Macronutrient.

  3. The answer is a. Macronutrient.

  4. The answer is a. Macronutrient.

  5. The answer is b. Micronutrient.

  6. The answer is false.

    Plants get carbon from the air as carbon dioxide.

  7. The answer is false.

    Although plants take minerals from the soil, the amount of these minerals is very small compared to the proteins, carbohydrates, lipids, and nucleic acids that make up the plant’s body. All these big molecules have a carbon backbone, so carbon atoms make up the majority of a plant’s weight. Plants get carbon from carbon dioxide in the atmosphere.