Thirsty Pot, Happy Pot

A week-long fair test with cress seeds: three matching pots, each missing one thing, so the child can see for themselves why a plant thrives or fails.

  1. Line three small pots or yoghurt cups with cotton wool or folded kitchen paper. Sprinkle the same pinch of cress seeds (or mustard seeds) on each.
  2. Label them with drawings the child makes: Pot 1 — water + light (windowsill, watered); Pot 2 — light, no water (windowsill, kept dry); Pot 3 — water, no light (watered, inside a cupboard or under a box).
  3. Ask for a prediction for each pot: “What do you think will happen to this one? Why?” Record it with a quick drawing.
  4. Each day the child waters pots 1 and 3 (a spoonful or two — damp, not flooded) and looks at all three.
  5. After 5–7 days put the pots side by side. Ask: “What is different? Why did this one not grow? Why is the cupboard one so tall and yellow?”
  6. Finish by asking the cause question backwards: “If we wanted pot 2 to grow, what would we have to do?” Then do it and watch.

Variation: once the cress in pot 1 is up, stop watering half of it (cut the cotton wool in two) and watch what happens over the next few days — the classic “it wilted because we forgot to water it.”

Requirements

  • Space: A windowsill plus a dark cupboard or a box to cover one pot
  • Surface: A tray or saucer under the pots
  • Materials: 3 small pots or yoghurt cups, cotton wool or kitchen paper, cress or mustard seeds, water, teaspoon, paper and crayons for labels
  • Participants: 1 adult + 1 child
  • Supervision: Light — a daily two-minute check together

Rationale & Objective

The subdomain’s first example is explaining “the plant died because we forgot to water it.” Rather than being told, the child here produces the evidence: three pots that are the same except for one thing. That is the heart of a fair test, and comparing them makes the cause visible. Inagaki & Hatano (2002) documented that young children come to explain living things in terms of what they take in — water and food make them grow — and that caring for a living thing deepens this causal understanding. The activity meets the NGSS kindergarten expectation to “use observations to describe patterns of what plants and animals (including humans) need to survive,” Head Start ELOF’s goals for planning investigations and drawing conclusions, and the EYFS expectation that children understand important processes and changes in the natural world. The final “what would we have to do?” question turns an explanation into a prediction.

Progress Indicators

  • Early: enjoys watering but treats the pots as unrelated; notices that one “didn’t grow” without saying why
  • Developing: predicts that the watered pot will grow; afterwards links one cause to one result (“no water, so no plants”)
  • Proficient: explains each pot’s outcome with its own cause (“this one had no water; this one had no light, so it went yellow”); says what to change to fix pot 2
  • Advanced: explains why the pots had to be the same apart from one thing; proposes a new test (cold versus warm, salty water) and predicts the result

Safety Notes

  • Seeds sold for sowing may be treated and are not for eating; if you want to eat the cress, buy seeds labelled for sprouting or salad and wash hands after handling
  • Keep seeds and cotton wool away from babies and toddlers who may mouth them
  • Damp cotton wool left for more than about ten days can go mouldy — bin it if it smells or shows fuzzy patches, and avoid sniffing it closely, especially for children with asthma or mould allergy
  • Some children feel sad or guilty about the pot that fails; explain that it was the plan, and let them “rescue” it with water at the end

Hints

  • Playfulness: name the three pots and give them characters — Sunny, Thirsty and Sleepy. The child becomes the “plant doctor” doing the morning rounds
  • Sustain interest: stick a daily photo or drawing on the fridge in a row so the change is visible; measure the tallest sprout with a strip of paper
  • Common mistake: changing two things at once (the dry pot is also in the cupboard) — then nobody can tell which cause mattered. Keep each pot one difference away from pot 1
  • Limited space: egg-cup halves on a windowsill work; an upturned mug makes the “cupboard”
  • Cross-domain: count the days (numeracy); draw labels and a results picture (early writing); taste the cress in a sandwich if food-safe seeds were used (healthy eating)
  • Progression: two pots, water versus no water → three pots adding light → child chooses the next thing to test → child sets up and tends the whole test with reminders only

Sources

  • Inagaki, K. & Hatano, G. (2002), Young Children’s Naive Thinking About the Biological World (Psychology Press)
  • NGSS K-LS1-1 — use observations to describe patterns of what plants and animals need to survive
  • Head Start ELOF — Scientific Reasoning (plans and conducts investigations and experiments; analyzes results and draws conclusions)
  • UK EYFS Understanding the World — The Natural World ELG; Development Matters (2021): “plant seeds and care for growing plants”
  • HighScope Science & Technology KDIs — Experimenting, Drawing conclusions, Natural and physical world
  • Montessori — botany and care-of-plants work in the Cultural Studies curriculum