Chard will stand a fair bit of winter weather. I grow perpetual spinach, erbette and chard and pick pretty much year round. Snow or really severe prolonged frosts will damage leaves. I pick off the bad ones and chuck them in the compost heap. They grow more.
Come spring, any which are still going strong will want to bolt. I pick them really hard and remove any tall flowering stems from the centres. You can keep them going a fair few extra weeks that way.
If I freeze, I remove the stems and slice the leaves into largish pieces, place in a colander and pour a kettle of boiling water over them. Once cool enough to handle, I squeeze out excess water, pack into ice cube trays and freeze. You can push them out of the trays and store in bags to save space. I'd also buy trays for the purpose as freezing greens and herbs in them, as I do, does turn them greenish.
If you have a dehydrator, sliced leaves can be dried as they are - raw, un-blanched - on a low heat like herbs if your machine allows for this. They dry fast and make useful jars of dried greens that are perfect for adding straight into curry, pasta sauce or soup.
As you may have guessed, I love plot greens of all sorts and happily eat them several times a week
