From what I have read on the subject, I think adding calcium would help by forming calcium oxalate before reaching the urinary tract, this way the stones are excreted instead. I am a big fan of green smoothies myself, although mine are usually brown since I use so much raw cocoa & mucuna pruriens. I do skip the cocoa occasionally and will make them really green with spirulina, mixing with chia seeds & hemp protein makes a long lasting smoothie with a good overall nutritional content including protein.
When Injustice Becomes Law, Rebellion Becomes Duty