What Can You Test in a Kratky Science Fair Project?
Change one thing and keep everything else the same. A Kratky science fair project works well because the setup is simple and cheap, so it is easy to grow several identical containers and test one variable, such as light, container color or nutrient strength.
Kratky also shows students something visible: roots growing down as the solution level falls. That makes it a good fit for projects from elementary school through high school.
Variables to Test
- Light: a sunny window vs a shaded one, or different hours under a light on a timer.
- Container color: clear vs covered containers, measuring algae and plant growth.
- Nutrient strength: half, normal and double the label rate.
- Air gap: starting solution levels that touch the net cup vs a container filled to the top.
- Water source: tap water vs rainwater vs bottled water.
- Plant variety: two lettuce varieties, or lettuce vs basil, in identical setups.
- Temperature: a cool room vs a warm room.
Pick one. A project that changes two things at once can’t show which one made the difference.
Setting Up a Fair Test
- Use the same container, net cup, growing medium and seed for every plant.
- Have a control group: the normal setup that you compare everything else to.
- Grow at least three containers per group, so one odd plant doesn’t skew the result.
- Label every container clearly.
- Start all the plants on the same day.
What to Measure
- Plant height, and number of leaves, twice a week.
- Solution level, marked on the outside of the container.
- Root length at the end, measured carefully.
- Fresh weight of the plant at harvest, on a kitchen scale.
- Photos taken from the same spot each time.
A simple table and a line graph of height over time make the results clear on a poster.
Timeline
Loose-leaf lettuce gives clear results in about four to six weeks. Start at least six weeks before the fair, and add a week for germination.
Safety for the Adult in Charge
- An adult measures and mixes the nutrient concentrate. It is not for students to handle directly.
- Use gloves and eye protection if the label says so.
- Label mixed solution clearly and keep it out of reach.
- Pick containers that won’t tip easily.
The roots without algae article shows how to let students see roots without spoiling the experiment.
Common Mistakes
- Testing several variables at once.
- Only one plant per group.
- Starting too close to the fair.
Common Questions
What is a good Kratky science fair question?
For example: “Does the amount of light change how fast Kratky lettuce grows?” Change one variable and keep the rest the same.
How long does a Kratky science fair project take?
About five to seven weeks with loose-leaf lettuce, including germination.
Is a Kratky project safe for kids?
Yes, with an adult handling the nutrient concentrate and the mixed solution labeled and kept out of reach.
Related guide: running a Kratky classroom project.
Related article: What Happens to Classroom Kratky Over Summer Break and Long Weekends?