coffee? what?

so during our plant unit, we did some experiments on plants to see what they needed to grow. we put one plant in a box and one plant outside of the box. we put flowers in food coloured water. and the last experiment, we have been watering one with water and the other with coffee.

now...what would be your hypothesis on what will happen to the coffee plant? when we started it, i thought it wouldn't grow as well as the watered plant. but then i started thinking, "well...coffee is just water...and people use coffee grounds in their gardens...maybe this plant will be okay..."

are you wondering how i can be a teacher and not know that coffee is good for plants? or are you not sure either? state your hypothesis.