While some herbs, particularly oregano and thyme, hold their flavor well when dried, very tender herbs need to be handled differently. Basil, mint, parsley and cilantro are good candidates for freezing instead.
Some herbs can be frozen as they are. Wash and dry them, spread them in a metal pan to freeze them, then store them in freezer bags. They’ll be limp when thawed, but you can use them in soups and sauces. That works for basil, chives and sage.
To keep the color bright, you also can chop herbs and cover them with a little water for freezing. Place them in plastic ice cube trays, add water to cover and then put the frozen cubes in resealable freezer bags. Drop the cubes in soups and stews.
A third method is chop herbs and cover with a little oil for freezing. The oil takes on the flavor of the herbs and can be used for sauteing or in a winter vinaigrette. Either water or oil works well for cilantro, parsley, basil, thyme or oregano.
Finally, for mint or lavender, you can make a flavored syrup by steeping the leaves in a hot mixture of half water and half sugar. It won’t get hard, but you can store it in the freezer for several months.
— Kathleen Purvis