Plant food: the nutrients and what each one is for
Light, water, and air. So why is this plant so pale?
- A · net pot & seedling
- B · roots
- C · air stone
It gets light and water every day. Something is still missing.
Think about a balanced dinner plate.
Each food on it helps your body in its own way. A plant needs a balanced plate too.
Plants need tiny building blocks from the water to grow.
Those building blocks are called nutrientsTiny bits of plant food that roots take in with water.
See it in the glossary. Growers often call them plant food.
- A · leaves
- B · roots
- C · flower
- D · stem
One nutrient helps a plant grow big, green leaves. It is called nitrogenA nutrient that helps a plant grow big, green leaves.
See it in the glossary.
Without enough, leaves turn pale, and the oldest ones go first.
Another nutrient helps roots grow and flowers bloom. It is called phosphorusA nutrient that helps roots grow and flowers bloom.
See it in the glossary.
It also helps the plant store and use energy.
A third nutrient keeps the whole plant strong. It is called potassiumA nutrient that keeps the whole plant strong.
See it in the glossary.
It helps the plant control its water and fight off sickness.
Plants also need calcium and magnesium, and a pinch of iron.
Calcium helps build firm new growth. Magnesium and iron help leaves stay green.
- N · nitrogen
- P · phosphorus
- K · potassium
- Ca · calcium
- Mg · magnesium
- Fe · iron
Your turn. Give each nutrient its job.
Tap a nutrient, then tap the job it does.
Which job does each nutrient do?
Tap a card, then a bin. Or press 1, 2 or 3 on a card.
- Nothing here yet
- Nothing here yet
- Nothing here yet
Which job does each nutrient do?
The answer:
Green leaves
- Nitrogen Nitrogen helps a plant grow big, green leaves.
- Magnesium Magnesium helps leaves stay green.
- Iron New leaves need a pinch of iron to turn green.
Roots and flowers
- Phosphorus Phosphorus helps roots grow and flowers bloom.
A strong, healthy plant
- Potassium Potassium keeps the whole plant strong.
- Calcium Calcium helps build firm, strong new growth.
Stuck? Green leaves have more than one helper.
Check 1 of 3
A plant's oldest leaves turn pale first. Which nutrient might be low?
Show the answer
Nitrogen. Right. Nitrogen helps a plant grow big, green leaves.
Check 2 of 3
Why does a plant need more than one nutrient?
Show the answer
Each nutrient does a different job. Right. Like foods on a plate, each one helps in its own way.
Check 3 of 3
Which nutrient does a plant need only a pinch of?
Show the answer
Iron. Right. A plant needs only a tiny bit of iron. It still matters.
You just learned which nutrients a plant needs and what each one is for.
Next up: Light and why it matters.
Go deeper: big helpings and tiny onesOpenClose
A plant makes its own food, a sugar, using light. Nutrients are better thought of as building materials and helpers than as food.
Nutrients a plant needs in large amounts are called macronutrients. Nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur are on that list.
Nutrients needed in tiny amounts are called micronutrients. They include iron, manganese, zinc, copper, boron, molybdenum, chlorine, and nickel.
Books differ on the total. Most count 16 or 17 essential elements, depending on whether they include nickel, and a few list more. Carbon, hydrogen, and oxygen come from air and water, not from plant food.
Plant food labels show three numbers, such as 10-10-10. They give the share of nitrogen, phosphorus, and potassium, in that order. Phosphorus and potassium are counted in special forms called phosphate and potash.
Calling those three “the big three” is a grower’s shortcut. Plant tissue usually holds more calcium than phosphorus, and hydroponic recipes add more calcium too.
Real plants are more complicated than “one nutrient, one job.” Each nutrient does many jobs, and they work together. Too much of one, such as potassium, can keep roots from taking up others.
Where a shortage shows up is a clue. Nitrogen can move from old leaves to new ones, so old leaves pale first. Iron barely moves, so new leaves show it first.
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. Link
- 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. Link
- Turfgrass Fertilization: A Basic Guide for Professional Turfgrass Managers. Penn State Extension, updated 2016. Link
- Westerfield, B., and M. English. Nutritional Deficiencies in Vegetables. Bulletin 1569. University of Georgia Cooperative Extension, 2024. Link
- Card, A., D. Whiting, C. Wilson, J. Reeder, and D. Goldhamer. Plant Nutrition. GardenNotes no. 231. Colorado State University Extension, 2015 (reviewed 2023). Link
- Spangenberg, B. Understanding Soil P & K. Wisconsin Horticulture, University of Wisconsin-Madison Division of Extension. Link
- Clark, M. A., M. Douglas, and J. Choi. "31.1 Nutritional Requirements of Plants." Biology 2e. OpenStax, 2018. Link
- Clark, M. A., M. Douglas, and J. Choi. "8.1 Overview of Photosynthesis." Biology 2e. OpenStax, 2018. Link
- Sánchez, E., and F. Di Gioia. Hydroponics Systems: Nutrient Solution Programs and Recipes. Penn State Extension, updated 2024. Link
- Jones, C., and K. Olson-Rutz. Plant Nutrition and Soil Fertility. Nutrient Management Module No. 2, 4449-2. Montana State University Extension, 2016. Link