A student wanted to see which type of fertilizer would make a plant grow taller faster, "Happy Plant" versus "Amazing Bloom".
He took a 1-month old tomato plant and a 1-month old rose plant, and put one cup of "Happy
Plant" fertilizer on the rose plant, and one cup of "Amazing Bloom” fertilizer on the tomato
plant. The student kept everything else the same - he watered both plants both the same, and
put them both next to each other in the sun. The student measured how much each plant grew
(in centimeters) after two month's time.
What is wrong?
Better experimental design: