wood ash/bugs

I read some where that wood ash mixed in with your soil will aid in the provention of bug. Does anybody know anything about this because I'm getting ready to start a new grow and before I mix up my medium I would like to know if there is any truth to this. I know it is good to throw your ash from your wood stove into your veg. garden over the winter but I don't know why.
Also I was told to mix coffee grinds into my medium mix, what the hell is this good for? I've been growing for quite a while and have never had any problems with my normal organic methods but I am always willing to experiment. Just want to know if any one has used either one of the methods and if so why before I kill my next crop. Thanx
redeyed