I have basil in window pots on my deck. They get full sun at least part of the day. I water daily if there has been no rain and the top of the soil is dry. There is good drainage, the water always drips out the bottom when I water. The plants were doing very well until a few days ago when the bottom leaves began to turn yellow. Does this mean that I am over watering? Underwatering? or some other problem. (there has been a lot of rain the last few days, but it has come in bursts for short periods of time).