I just got in and started to farm. Nice work! I'm really enjoying it so far. One thing that crosses my mind, if seasons/sun and whatnot play a part in the plants growth/life, what about rain? Shouldn't it add to the water levels of the plants as well? No idea if that's possible or not, but it'd be cool if it helped with watering. =)

Another suggestion would be to change the layout of the plant status a bit.

Something like

<---- Harvest Level---->
<Sun> <Weeds>
<Water> <Pests>
<Fertilizer>

This puts all of the positive things on the left, negative on the right and the overall level of the plant across the top of them all.