I have trouble getting low in my attempts at "ass to grass" squats. I have realized my calves are to blame for lack of motion what should I do to improve their flexibility?
For me it sounds as if you are doing squats the wrong way. Your knees should never go over your toes, but rather be in line with your feet. Your shanks should stay in place - mostly. The saying is "ass to the grass" and this is what the movement is like, your behind is moved towards the floor behind your heels. Your weight should be on your heels and the balls of the feet.
For a more comprehensive discussion of how squats are done right, please see http://www.nerdfitness.com/blog/2014/03/03/strength-training-101-how-to-squat-properly/