Keeping your greens fresh

I try to avoid dairy.  When my daughter was born and I started breastfeeding, I was told she had colic.  She cried all the time.  ALL THE TIME.  So after some research I found the a lot of colic is actually a baby's inability to digest dairy.  I was desperate, I gave up dairy.  And magically, within a week, completely gone.  Unless I went crazy and ate pizza then she got sick again.  And after giving it up, I never felt better myself.  I'm not perfect, I eat some dairy occasionally, but overall, I try to avoid it.  That's my round about way of talking about greens.  They're a good source of calcium, so I try to eat more of them.  Sometimes, I leave them in the fridge too long and they get all limp and gross looking.  The night before I plan on cooking them, I put them in a vase of water and they perk back up.  I do this with kale and mustard greens mostly.  Don't leave them in there too long, because they start to lose their color, become less green.  I'm not sure if that means they will lose their nutrients, so just to be safe, I only keep them in there about overnight.