To answer your question, yes, you need to "blanch" the terrestrial greens in hot water. Just get some water boiling and throw the veggies in for 30 seconds or so. It helps break down some of the plant cells that fish cant do on their own.
And definitely it helps to wash them, I would do a fresh water rinse on them, then boil them, then probably rinse again real quick. You really dont want to put pesticides into your tank.
Plus, most terrestrial greens are high in phosphates from fertilizer, so know that you'll be adding that to your tank.
I agree with the other who who said they dont do it, I wouldnt recommend it either, but if you're going to, then there ya go.