Blanching vegetables can help them retain their texture and flavor while they’re stored in the freezer, but some vegetables (and fruits we refer to as “vegetables”) don’t fare so well even with that extra step. When in doubt, consider the water content and intended use. Cucumbers, zucchini, tomatoes, and celery will all lose a bit their snap and structure when frozen.
If you’re planning on chucking a tomato in some sauce, or some celery into a soup, the softer mouthfeel won’t make much of a difference. (Freezing tomatoes actually makes them super easy to peel.) Just don’t try and add any frozen cucumber slices to your salad, and you’ll be fine. (Save those for a spa treatment instead). Never freeze lettuce or cabbage though, unless you plan to puree them into soup.