Lesson guide · Lesson 4 · Grades 3–8 · 6 min

Plant food: the nutrients and what each one is for

What nutrients are, the three a plant needs in big helpings, and the job each one does.

Open the lessonPrintable worksheet

Students will

  • Explain that nutrients are building blocks a plant takes in through its roots.
  • Name nitrogen, phosphorus, and potassium, and give one job for each.
  • Explain that a plant needs some nutrients in big amounts and others in tiny amounts.

New words

nitrogen
A nutrient that helps a plant grow big, green leaves.
phosphorus
A nutrient that helps roots grow and flowers bloom.
potassium
A nutrient that keeps the whole plant strong.

Talk about it

Your dinner plate has different foods for different jobs. How is a plant's plate like yours, and how is it different?

Check questions and answers

  1. A plant's oldest leaves turn pale first. Which nutrient might be low?

    • Nitrogen (answer) Right. Nitrogen helps a plant grow big, green leaves.
    • Calcium Not quite. Calcium helps build firm new growth. Think about green leaves.
    • Iron Not quite. Iron trouble shows on new leaves first. Think about old ones.

  2. Why does a plant need more than one nutrient?

    • Each nutrient does a different job (answer) Right. Like foods on a plate, each one helps in its own way.
    • One nutrient can do every job Not quite. Think about the plate. Each helping does something different.
    • More kinds make the water look nicer Not quite. Nutrients are for the plant, not for looks.

  3. Which nutrient does a plant need only a pinch of?

    • Iron (answer) Right. A plant needs only a tiny bit of iron. It still matters.
    • Nitrogen Not quite. Nitrogen is one of the big helpings.
    • Potassium Not quite. Potassium is one of the big helpings.

Sources

  • Sánchez, E., F. Di Gioia, R. Berghage, N. Flax, and T. Ford. Hydroponics Systems and Principles of Plant Nutrition: Essential Nutrients, Function, Deficiency, and Excess. Penn State Extension, 2026.
  • Gatiboni, L. "1. Soils & Plant Nutrients." In Moore, K. A., and L. K. Bradley, eds. North Carolina Extension Gardener Handbook, 2nd ed. NC State Extension, AG-831, 2022.
  • Turfgrass Fertilization: A Basic Guide for Professional Turfgrass Managers. Penn State Extension, updated 2016.
  • Westerfield, B., and M. English. Nutritional Deficiencies in Vegetables. Bulletin 1569. University of Georgia Cooperative Extension, 2024.
  • Card, A., D. Whiting, C. Wilson, J. Reeder, and D. Goldhamer. Plant Nutrition. GardenNotes no. 231. Colorado State University Extension, 2015 (reviewed 2023).
  • Spangenberg, B. Understanding Soil P & K. Wisconsin Horticulture, University of Wisconsin-Madison Division of Extension.
  • Clark, M. A., M. Douglas, and J. Choi. "31.1 Nutritional Requirements of Plants." Biology 2e. OpenStax, 2018.
  • Clark, M. A., M. Douglas, and J. Choi. "8.1 Overview of Photosynthesis." Biology 2e. OpenStax, 2018.
  • Sánchez, E., and F. Di Gioia. Hydroponics Systems: Nutrient Solution Programs and Recipes. Penn State Extension, updated 2024.
  • Jones, C., and K. Olson-Rutz. Plant Nutrition and Soil Fertility. Nutrient Management Module No. 2, 4449-2. Montana State University Extension, 2016.