You buy an enormous bag of greens with the best intentions of making a nutritious smoothie every morning, but by day two, the fire under your smoothie obsession starts to fizzle out. And when you finally go to pull out that container a few days later, your heart sinks a little when you find yet another bag of wilted, slimy spinach. Here's a simple solution for preserving those greens: freeze them instead.
Freezing your greens will save you the heartache of throwing out spoiled produce, and you can buy in bulk, which is much cheaper than picking up small containers. It'll also save you time if you buy your greens like curly kale or swiss chard in bunches, since you can do all the prep work ahead of time. And since smoothie-making  is now that much faster and easier, you're more likely to make one instead of pouring a bowl of sugary cereal. Any type of greens will freeze well, so whether you prefer spinach, kale, chard, beet greens, arugula, or a combination, your green smoothies are practically made after these simple steps.
Since some greens like spinach can pull apart pretty easily once frozen, you could throw the whole bag in the freezer. But if you're worried about whether it's safe to freeze those produce bags, you're better off using pint-sized freezer bags and freezing individual servings. It'll save you space in the freezer, since it's easier to stack these small bags, and you can also reuse them. If you're buying bunches of kale and spinach, then wash and chop them before placing one- to two-cup servings in each freezer bag.
Pick up some BPA-free ice cube trays or baby food trays  — I like the ones with lockable lids, so the trays can be stacked — and buy a variety of greens. You can puree them separately in a food processor or blender or puree them together, adding a little water to yield a smooth consistency. Pour into the little wells, attach the lids, and freeze them. Once the cubes are frozen, you can leave them in the trays or pop them out into gallon-sized freezer bags. When you're ready to make your smoothie, just grab a few and throw them in your blender — it's a great time saver. Just for reference, a packed NutriBullet (about four firmly packed cups) of kale with 1/3 cup water makes 12 one-ounce ice cubes, so if you want to add one cup of kale to your smoothie, then use three ice cubes. Aside from smoothies, here are some other ways you can use your frozen greens .