• Use all frozen fruit—not just berries. The frozen rule goes for all of your fruit. If you aren't using a banana, frozen mixed berries will also add thickness (we just really hate blending ice). If your blender has a hard time with big, chunky, frozen strawberries, let them thaw for a couple of minutes and chop them into smaller pieces. And use other fruits; frozen peaches are great, as are frozen tropical fruits like pineapple and mango.
• Add peanut butter or nuts. We like the idea of something heartier and less summer-in-a-glass when it's frigid outside. This Frozen Banana Peanut Butter Chocolate Chip Milkshake is more of a dessert, but you could omit the chocolate chips and call it breakfast. Or add some chopped almonds or walnuts.
• Use tofu. This is another good year-round tip, but in the winter, it's nice to have alternative ingredients when fruit runs low. Tofu adds a good protein and texture. Try this Low-Sugar, High-Protein, Dairy-Free Smoothie.
• Add ground-up oatmeal. Just another way to give a smoothie some heft and warmth (can we call it warmth?), especially if you're limited on fresh ingredients. Here's a post all about it. We're imagining a banana, oatmeal, yogurt smoothie with some honey or maybe flax seeds.
• Freeze some yogurt and add oranges. Citrus is plentiful right now, but it doesn't exactly give you a soft, creamy texture. Try freezing some vanilla yogurt (almost like adding ice cream!) and making a creamsicle-ish smoothie.
Related: Winter Smoothies: 5 Seasonal Add-Ins
(Image: Stay Young Smoothie, from MarthaStewart.com)