It is okay to freeze plums. They should be washed, peeled, cut in half and pitted first, and slices or pieces can then be placed onto a baking pan and frozen. Once frozen, the plums should be transferred into freezer containers until ready to use.
Plums with skin that has no wrinkles, soft spots or blemishes are best for purchase. A gray sheen called a bloom may be present but does not affect quality. It indicates excessive handling between the production process and arrival at the store.
Hard plums have not ripened yet. Ideal plums are firm with a slight give but should not be soft.