Lesson guide · Lesson 11 · Grades 3–8 · 6 min
Nutrient strength: the soup test
Why plant food can be too weak or too strong, and how growers measure its strength.
Students will
- Explain that plant food in water can be too weak or too strong.
- Describe one sign of food that is too weak and one of food that is too strong.
- Say what an EC meter measures and how to raise or lower the reading.
New words
- EC
- A number that tells you how strong the plant food in water is.
Talk about it
When is more of a good thing too much? Think of salt, sun, or sleep.
Check questions and answers
The leaf tips are brown and crispy. The EC reads very high. What do you do?
- Add plain water (answer) Right. Plain water makes the plant food weaker.
- Add more plant food Not quite. The food is already too strong. More makes it worse.
- Turn off the light Not quite. Light isn't the problem here. Look at the EC number.
What does an EC meter tell you?
- How strong the plant food is (answer) Right. More food in the water gives a bigger number.
- How sour the water is Not quite. That's what pH tells you. EC is about how much food is mixed in.
- How warm the water is Not quite. A thermometer tells you that. EC is about food.
The whole plant is pale and grows slowly. The EC is very low. What is going on?
- The food is too weak (answer) Right. There isn't enough food in the water, so the plant stays hungry.
- The food is too strong Not quite. Strong food shows up as brown leaf tips. A low number means weak.
- The roots have too much food Not quite. A low EC means there is very little food in the water.
Sources
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