Plants get their food from the soil
A widespread KS2 and KS3 science misconception. Pupils believe plants take in food from the soil through their roots, rather than making it by photosynthesis.
- Evidence
- Strong
- Subject
- Science
- Key stage
- KS2, KS3
- Citations
- 4
“Plants take in food from the soil through their roots. Soil is their food.”
Plants make their own food (glucose) in their leaves, from carbon dioxide and water, using energy from sunlight. Soil supplies water and a small number of mineral nutrients, not food.
Diagnostic items
Use these to surface the misconception before teaching the corrective sequence. The target distractor is what most pupils with this belief will choose.
- 1
A young oak tree weighs 1 kg. Fifty years later the same tree weighs 1,000 kg. Where has the extra 999 kg of material mostly come from?
- A.The soiltarget distractor
- B.The air (carbon dioxide)
- C.The water in the rain
- D.The sun
Source: Adapted from Driver et al., 1985
- 2
What do plants need in order to make food?
- A.Soil, water, and warmthtarget distractor
- B.Sunlight, carbon dioxide, and water
- C.Fertiliser and water
- D.Oxygen and sunlight
Source: AAAS Project 2061 misconceptions database
Of all the misconceptions in primary and lower-secondary science, this is the canonical example. It is the misconception research itself was built on. If you teach photosynthesis without surfacing it directly, pupils will sound correct on a written test while still holding the alternative theory in their heads.
Why it persists
Three reasons.
Everyday language does most of the work. “Plant food” is the brand name on every fertiliser bag, and gardeners use the phrase without thinking. The biology then runs counter to visible evidence: a 1,000 kg tree gains almost all its mass from invisible carbon dioxide, through gas exchange too slow to watch. And photosynthesis is taught as a chemical equation before many pupils have a confident grasp of gases as matter, so they can recite the equation while still picturing food coming up through the roots.
Evidence
Strong evidenceAmong the most replicated findings in science education research. Documented across age groups, countries, and curricula since the 1980s. The intuitive theory (that plants eat soil) is what cognitive scientists call a robust alternative conception, meaning it resists ordinary teaching unless directly addressed.
Research citations
- Driver, Guesne & Tiberghien(1985)Children's Ideas in Science (chapter on plant nutrition)BookFieldPositivePopulation: KS2 and KS3 pupils, UK
- Bell(1985)Students' Ideas about Plant Nutrition, What Are They?Cross-sectionalFieldPositivePopulation: New Zealand pupils aged 7 to 17
- AAAS Project 2061Atlas of Science Literacy, Strand on Living EnvironmentReviewMeta
- Hershey(2004)Avoid Misconceptions When Teaching about PlantsReviewFieldPositive
Caveats
- The misconception is persistent. A single lesson addressing it directly is rarely enough.
- Pupils who can correctly explain photosynthesis in a quiz often revert to the soil-as-food model when reasoning informally.
Populations studied
- UK primary and secondary pupils
- US K-12 students
- International samples (NZ, Australia, several European countries)
Corrective approaches
Pedagogies and tasks with evidence for addressing this misconception.
Refutation text
Begin the lesson by stating the misconception explicitly and then refuting it with evidence. The contrast is the mechanism.
Frayer model with non-examples
Use the non-examples quadrant of a "photosynthesis" Frayer to explicitly include "the plant eating soil" so the lookalike is named and rejected.
The Van Helmont willow tree experiment
A 17th-century experiment that weighed a willow tree before and after five years of growth in carefully measured soil. The soil lost almost no weight; the tree gained 74 kg. A classic concrete demonstration.
Concept cartoons
Present three pupil voices, each holding a different view about where the tree's mass comes from. Pupils argue for one and against the others.
Hexagon concept maps
Place "soil", "water", "carbon dioxide", "sunlight", "glucose", and "growth" on hexagons and ask pupils to arrange them showing the actual flow of matter.
Try this in Chalk
Related concepts
Questions teachers ask
At what age does this misconception appear?
Is using the word "plant food" in class harmful?
How do I know if my class still holds this misconception after teaching?
Frayer Model
Vocabulary instruction template with definition, characteristics, examples, and non-examples.
Open Frayer Model