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* * * Plants and pH * * *
My Experiment

The experiment I carried out was based on plants and pH. The aim was to see what pH a certain plant would grow best at. I used five identical broccoli plants and watered them each with a different substance with a different pH level. These substances were all very different from each other and because of this each plant grew differently. If the experiment had been repeated using different substances, but the same pH levels, the results would have been different, but the same conclusions could have more or less been drawn.

  • Universal indicator solution or pH paper
  • Five substances with the pH levels of 4.5, 6.0, 7.0, 7.5, 8.5. (orange juice, eno, water, pond water, egg white) 
  • Five identical, small broccoli plants or any other plants in a small pot
  • Labels
  • Measuring cylinder or measuring cup
  • five identical plastic cups or beakers
  • Measuring tape
  • Digital camera


The substances used in trial 1 of my experiment
orange juice, eno, water, toothpaste, egg white


  1. The pH of a variety of substances were tested. They were diluted with water so they became less concentrated. Five substances were chosen that had a pH of 4.5, 6.0, 7.0, 7.5 and 8.5. These substances were orange juice, eno, water, pond water and egg white.
  2. Five identical, small broccoli plants in small pots were purchased. There heights were measured and recorded.
  3. The five plants were labeled with the pH it would be watered with.
  4. A measuring cylinder was used to measure 10mL of each substance, which were then placed in separate identical plastic cups. The plastic cups were labeled with the pH and substance it contained inside (the same cup was used for the same substance throughout the experiment).
  5. A measuring cup was used to measure 50mL of water which was added to each substance. This diluted each substance.
  6. Each substance was watered with its matching broccoli plant.
  7. Steps 4, 5 and 6 were repeated every two days. The heights of each plant was also measured and recorded at the same time.
  8. Digital photos of each plant were taken twice a week.
  9. Repeat the experiment. This will be trial two. Compare the results from both trials for a more accurate result.

 Controlled Variables

When doing this experiment it’s vital that you make sure that variables are controlled properly throughout the entire experiment. Any changes could alter the result, therefore giving you an inaccurate result. The controlled variables that need to be kept the same while conducting this experiment are:

        The plants: They all must be of the same kind eg broccoli plants. As well as this they must all be in pots of relatively the same size as it may change the outcome of the experiment. Also each plant has a specific pH it is being watered with. This cannot change during the experiment; it must stay the same. For example if one plant is being watered with the substance that has a pH of 4.5, a week later it cannot be watered with the substance that has a pH of 6.0. If this happens there is no point at all to the experiment. How is it possible to draw conclusions from it?

        The substances: Once the five substances have been chosen they are the ones that must be used. Substances cannot be changed half way through the experiment as the results will change entirely and accurate conclusions cannot be drawn.

        The quantity of the substances: Each plant must be watered with exactly the same amount of each substance (50mL of water and 10mL of each particular substance).

        When the plants are watered: Each plant should be watered at the same time. The time between each watering should be kept the same eg every two days. This must be kept constant throughout the experiment.

        The measuring cup: The same measuring cup should be used during the experiment so that you can be sure the amount of substance each plant is being watered by is exactly the same. Some measuring cups or beakers may be not be accurate and if more then one is used during this experiment the amount of substance used on each plant may be altered slightly each time they are watered. This too will change the results of the experiment.

        The cups: The cups used to water each plant should be kept the same throughout the experiment. Each cup should have the same substance put in it each time. For example the substance with a pH of 4.5 should be placed in the same cup each time the plants are being watered. This is because when the plants are watered a small amount of the substance is usually left in the cup, if another substance is put in there, the pH may change, altering the experiment.

        The measuring tape: The same measuring tape must be used to ensure accurate results.

        The way the plants are measured: The way the plants are measured needs to be done exactly the same each time (measuring their height from the top of the soil to the tallest leaf).

        The position of the plants: Each plant must stay in the same spot from the beginning to the end of the experiment, especially if more then one trial is done. If they are moved they may grow differently depending on the amount of sunshine they receive and precise results cannot be drawn.

        The length if each trial: The length of each trial must be kept the same eg 3 weeks.

These are a few of the variables that need to be controlled

Intel Young Scientist 2004