Use a clear jar with a sleeve that slides off. Students lift the sleeve to look at the roots and the falling water level, then slide it back. Algae needs steady light, so brief looks don’t cause a problem.
Why Not Just Use a Clear Jar?
Light reaching the solution grows algae within days to weeks. The water turns green, the roots get coated, and the plant suffers. Covering the jar between looks prevents that.
Making a Sleeve
- A sock or fabric tube pulled over the jar
- A sheet of dark card rolled into a tube and taped
- A cardboard tube cut to the jar’s height
Students can decorate their own sleeves and write their name on them.
Making It a Lesson
- Lift the sleeves once a week and mark the water level on a strip of tape.
- Draw the roots: how long, what color, how many branches.
- Talk about why the roots above the water line look different from the ones below.
A Control Jar
For older students, leave one jar uncovered on purpose and compare it with the covered ones after a few weeks. It shows clearly why the sleeves matter.
Related guide: running a Kratky classroom project.
