Ginger has a very distinctive punch. When a recipe calls for fresh ginger and you're out of it, you have options. While there's no exact dupe for the distinctive root, you can substitute similar or complementary spices that can equally enhance your recipe. They will change the final product a little bit from what it was originally meant to be, but that can be a good thing.
Ground ginger is going to be much milder and less astringent than fresh ginger, without the essential oils that give it its kick. Depending on how old your ground ginger is, its flavor could be even more diminished. But if you're in a pinch, it's probably the best thing. Use 1/4 teaspoon of ground ginger for every 1 tablespoon of fresh ginger called for in a recipe.
Keep in mind, however, that it usually doesn't work the other way around. That is, fresh ginger typically does not substitute for ginger powder in dessert recipes. As mentioned, it's rather astringent and has quite a different flavor profile. In this case, you're better off substituting another spice altogether.
If you're making a bread, baked good, or dessert that calls for ground ginger, an equal amount of allspice, cardamom, cinnamon, mace, or nutmeg just might work. It's not that allspice or cinnamon tastes like ginger, but that they're complementary spices. Pumpkin pie spice is another option to consider. It's typically a blend of ginger, cinnamon, nutmeg, and allspice. These substitutes will change the flavor and color of the dish slightly but will work just fine in a pinch. When doing this, add 1/2 the amount of ground ginger called for, and go from there, tasting as you go.
Crystallized ginger is also known as candied ginger or glace ginger (glace means ice in French, and this ginger looks like it's coated in ice crystals). It's basically fresh ginger that has been cooked in sugar water and rolled in sugar. If you have a recipe that calls for this ingredient, you can substitute 1/8 teaspoon of ground ginger for every tablespoon of crystallized ginger. You may need to add sugar, to taste, to compensate.
That works out to 1 teaspoon of ground ginger for every 1/2 cup of crystallized ginger. If your recipe uses crystallized ginger as a garnish, choose something else, or omit it. Ground ginger won’t be a good substitute in this situation.
Freezing and Storing
Fresh ginger freezes beautifully. Keep a ginger root in your freezer, and pull it out whenever you need it for a recipe. You don’t even have to thaw it first. Just grate as much as you need, and stick the rest back in the freezer for next time.
There are a few tricks for storing ginger properly. You can even ensure that you have ginger on hand when you need it by growing the flowering plant on your windowsill.