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Science

What Do Plants Need to Grow?

Overview

Children set up a simple investigation to find out whether plants need water, light, or soil to grow, then observe the results over time.

Learning Objective
Children investigate what plants need to grow by comparing plants grown under different conditions.

Resources needed

  • Seeds (any fast-growing type)
  • Soil
  • Three containers
  • Water

Lesson stages

0 / 7 done
  1. 1 Ask: what do you think plants need to grow?
  2. 2 Set up three pots with seeds: one with water and light, one with water but no light, one with light but no water.
  3. 3 Predict: which plant will grow best?
  4. 4 Observe and record daily for one to two weeks.
  5. 5 Compare results: which plant grew best? Which worst?
  6. 6 Discuss: why is it important to change only one thing at a time?
  7. 7 Introduce: this is called a fair test.

Tap a step to mark it as done.

Variations

  • Also test with and without soil — grow a seed in water only.
  • Test different amounts of water — too little vs just right vs too much.
  • Add a fourth variable: different soil types.
More information

Teach: seed, germinate, variable, fair test, condition, light, water, soil, observe, record. The concept of changing only one variable is the key scientific idea to introduce.

Focus on just one comparison — water vs no water — rather than multiple conditions for younger children.

Can children explain why only one thing should be changed in a fair test? Can they describe the results and connect them to what plants need?

Use any available seeds — those from food crops are ideal. Containers can be old cans, cut bottles, or folded leaves. Water from any source.

Children often think plants eat soil. Clarify that soil provides support and minerals but plants make their own food from sunlight, water, and air — not from soil.

This investigation introduces fair testing — the principle that good experiments change only one variable at a time. It is one of the most important concepts in scientific methodology.

Activity details
Primary Medium 20 minutes setup, observation over 1–2 weeks 10 minutes prep Small Group, Whole Class Indoor & Outdoor
Topics
Plants Growing Conditions Fair Testing