Whenever you play a level, win new stars, help friends or beat Rancid you will be rewarded with growth that will be added to your Show Cropsie. Playing many aspects of the game will contribute to overall growth, so keep playing and tending to your plant.
Once your Show Cropsie reaches a certain level of growth, it will rank up to the next tier. Try to make it all the way to tier 1 for the best rewards!