You can tell by picking up the pot... is it heavy? Or really light ? if you can't figure it out, fill a bucket with dry soil.. pick it up, then water it.. pick it up. You'll see..
As far as foliar feeding with buds.... use your hand and hold the leave from the top, blocking everything behind it.... spray the bottom of the leaves (spray the ones most affected first)do this when your lights first come on, and probably again later in afternoon. If you're relatively careful you can avoid spraying on the buds