Track 2 · Lesson 9

The nutrient solution

6 minutes · 1 ordering activity

With no soil, where does a plant’s food come from?

A plant in water gets nothing from dirt. All of its plant food is in the water.

The water looks plain. What is hiding in it?

Think about juice made from a thick syrup. You read the label.

Then you mix a little syrup into a lot of water.

Too little syrup, and it tastes like plain water. Too much, and it is far too strong.

The recipe gets it just right.

Plant food comes as a strong liquid or a powder. It is much too strong to use as it is.

This strong form is called a concentratePlant food that is very strong. It gets mixed into lots of water before use.
See it in the glossary.

Concentrate can sting your eyes and skin, and you must never drink it.

An adult always measures and pours it. You can help with the water.

Mix the right amount of food into water, and it spreads all through it. Now every drop carries food.

This mix is called a nutrient solutionWater with plant food mixed all through it.
See it in the glossary.

  • A · measuring jug
  • B · marks
  • C · plant food
  • D · small measuring cup

Some plant food comes in two bottles, part A and part B. Each part goes into the water on its own.

Poured straight together, they make solid bits that can clog pipes.

Start with the water, then add the food and stir well.

Last, test the water before it goes to the plants. The next lessons show you how.

Your turn. Put the mixing steps in order.

An adult does every step that touches the plant food.

Put the mixing steps in order.

Move the steps up or down. Then check.

  1. Read the recipe on the label. Right spot Not quite
  2. Fill the jug with water up to the mark. Right spot Not quite
  3. Test the water, then pour it into the tub. Right spot Not quite
  4. Stir until it is all mixed. Right spot Not quite
  5. The adult pours it into the water. Right spot Not quite
  6. An adult measures the plant food. Right spot Not quite

Put the mixing steps in order.

The right order:

  1. Read the recipe on the label.
  2. Fill the jug with water up to the mark.
  3. An adult measures the plant food.
  4. The adult pours it into the water.
  5. Stir until it is all mixed.
  6. Test the water, then pour it into the tub.

Water goes in first, then the food. Stir, then test before the plants get it.

Check 1 of 3

What is a nutrient solution?

Show the answer

Water with plant food mixed all through it. Right. The water carries the food to every root.

Check 2 of 3

Who measures and pours the concentrate?

Show the answer

An adult. Right. Concentrate can sting eyes and skin.

Check 3 of 3

You add twice the plant food the recipe says. What happens?

Show the answer

The water gets too strong for the plant. Right. Like juice with too much syrup, it is too strong.

You just learned how to mix a nutrient solution from a recipe.

Next up: pH: the nutrient lock.

Next lessonCourse map
Go deeper: what is in the bottle

Plants need 17 elements. They take carbon, hydrogen, and oxygen from air and water, and the rest from the nutrient solution. Nickel was the last one added to the list, so some older books list 16.

They need nitrogen, phosphorus, and potassium in large amounts, and tiny amounts of others such as iron, zinc, and boron.

Two-part plant foods keep calcium apart from sulfate and phosphate. Mixed strong, these form solid bits that can clog pipes and drippers. Once diluted in plenty of water, the parts mix safely.

Too much plant food harms plants too. Very salty water can burn leaf edges and kill roots.

Growers measure the strength of a solution with a meter that reads electrical conductivity, called EC. Lesson 11 covers it.

Plants take up water and food at different rates, so the solution changes as they grow. Growers top it up and replace it from time to time.

Products differ, so always follow the label for the amount of each part.

Sources

  • Hart, C. Home Hydroponics (handouts). University of Illinois Extension. Link
  • Hoagland, D. R., and D. I. Arnon. The Water-Culture Method for Growing Plants without Soil. Circular 347. University of California College of Agriculture, Agricultural Experiment Station, 1938. Link
  • Kratky, B. A. Fertilizer Stock Solutions: For Lettuce. University of Hawaii CTAHR. Link
  • Kratky, B. A. Three non-circulating hydroponic methods for growing lettuce. Acta Horticulturae 843: 65-72, 2009. Copy hosted by the University of Hawaii CTAHR. Link
  • Sánchez, E., and F. Di Gioia. Hydroponics Systems: Using the Two Basic Equations to Calculate a Nutrient Solution Recipe. Penn State Extension, 2026. Link
  • 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
  • Hochmuth, G. J. Production Systems. Florida Greenhouse Vegetable Production Handbook, Vol 2. CV255. UF/IFAS Extension. Link
  • Eason, H. 'Set It and Forget It' Hydroponic Lettuce. HS1488. UF/IFAS Extension. Link
  • Singh, H., and B. Dunn. Electrical Conductivity and pH Guide for Hydroponics. Fact sheet HLA-6722. Oklahoma State University Extension, 2017. Link
  • Dunn, B. Hydroponics. Fact sheet HLA-6442. Oklahoma State University Extension, 2025. Link
  • National Center for Biotechnology Information. Calcium nitrate (CID 24963), GHS classification. PubChem, National Library of Medicine. Link
  • National Oceanic and Atmospheric Administration. Calcium nitrate. CAMEO Chemicals. Link

All sources · Corrections