I suggest that if a plot has been recently watered (bar is full), it have a darker brown color than if it's wet, but ready for re-watering. (Right now, there are two colors: dry and wet; I propose a third for soaked.)
This would make it easy to scan a set of plots and visually determine if you forgot to water any of them after planting in the case where they were already wet to start (plant/water).