Wash, stem, and pit the cherries. A cherry pitter tool makes this job dramatically faster and less messy, and is a worthwhile purchase if you freeze cherries regularly. You can freeze cherries unpitted, but removing pits before freezing is far more convenient for later use.
For sweet cherries: flash freeze pitted cherries on a parchment-lined sheet pan. Once solid, transfer to freezer bags. Sweet cherries generally do not need sugar treatment.
For tart/sour cherries (pie cherries): tart cherries benefit from a sugar pack. Toss pitted cherries with ¾ cup sugar per quart of fruit. Let sit until juices flow, then pack into containers with ½ inch headspace. Alternatively, flash freeze and pack without sugar if you want to control sweetness when baking later.
8 to 12 months.
For pies and baked goods: use directly from frozen — measure the frozen cherries and add to the recipe. They may add a minute or two of baking time. For eating: thaw partially in the refrigerator. For smoothies: use frozen.