You’ve set up an experiment to test whether spraying the lea…

You’ve set up an experiment to test whether spraying the leaves of your plants with water keeps them alive longer than just watering the soil. For half of your plants you water the soil each day and spray the leaves with water each day. For the other half of the plants you only water the soil. This goes on for one month and then you check how many plants in each group are still alive. Based on the description above, what is a controlled variable in this experiment?