Semps can definitely get too dry as well. Its a problem for me, mostly in the winter, or when we get an extended dry spell with no rain and lots of sun. I must confess, I've been watering my semps every other day for the past couple of weeks, because we are in an extended period of no rain and high heat (90's). The relatively fast mix they are in allows the water to drain away quickly so they don't sit in it.
