Adding greens to smoothies can be a great way to balance out their nutritional profile. Baby spinach is the best green to start with because it’s so mild. I was surprised to find that I can easily add a 1/4 lb of baby spinach to a 4-cup fruit smoothie, and not have it taste like vegetables (not that I’m against the taste of vegetables; I’m all for a nice savory vegetable smoothie).
I buy pre-washed organic baby spinach and add it directly to the blender. Some people say you should wash it again before using it, but generally I like to go with the convenience of just tossing it in, and I’ve never had any problem. If I were preparing smoothies for someone with a weak or compromised immune system I might be more careful.
Some weeks I buy other greens (such as kale, chard, lettuce, or collards) for variety, but baby spinach stands out as the easiest to use. The others can have a strong flavor that you have to manage more carefully. With spinach you run out of space in the pitcher before you can add too much. So go ahead, make Popeye proud!