They're not as interchangeable as you might think.
Because the universe is an unjust place, it usually is safe to assume that the option that requires more effort is going to be the better option. That said, there are times when you can take that shortcut that will save you a bit a time, while still achieving a final result that is something to be proud of. This is exactly the case when it comes to adding garlic to your food. Fresh garlic requires peeling and or chopping/mincing* (read: you have to take out a cutting board and a knife, and then at some point, muster up the strength afterwards to clean both).
In the case of garlic powder, all you need to do is whip open the ol’ spice cabinet, and give your jar a gentle tap over your food (read: there is no clean-up involved, so this is obviously the more enjoyable option). While there is most definitely a place and time for this low-maintenance granulated version, there are certain circumstances where you have to buckle down and opt for the fresh stuff.
Let’s start with what garlic powder actually is—it’s a ground and dried out version of the fresh garlic bulb. You might also hear it referred to as “granulated garlic”—that’s the same thing, only ground a tad bit coarser. One huge advantage of using this versus fresh garlic is that it’s less prone to burning. If you try to saute it directly in oil or butter like its fresh counterpart, then yes, it will burn. But, if you’re baking or broiling something (GARLIC BREAD, HELLO) and you want to incorporate a garlic flavor, your best bet is to go for garlic powder. If we’re talking dry rubs for meats and veggies, garlic powder is superb option—fresh garlic, no matter how beautifully you mince it, will not disperse as easily and readily, or stick as well to the food. However, because this form of garlic has been dried out (and has probably sat in your cupboard for longer than you’d like to admit), it’s likely lost some of its potent flavor in the same way that all spices do as time passes. So, if you’re trying to create a smack-you-in-the-face garlic flavor, I’d suggest you put down the jar of garlic powder. For soups, stews, dips, or sauces where garlic is only a minor flavor component, rather than a star ingredient, you’ve got the green light for garlic powder.
OK, It’s time to bring out the big guns (A.K.A. the fresh stuff)—for times when there’s no getting around that signature fresh garlic flavor. Pasta dishes, pesto, stir-fries, whole-roasted cloves, and tomato sauces are all situations where you’re probably better off going for fresh garlic. Sure, you can use garlic powder in all of these situations, but the flavor won’t be as vibrant, and the overall taste of your food will suffer slightly. If that minor downgrade in your food is worth having to do less work, then you go ahead and own that laziness! But if you’ve got it in you, consider going for fresh garlic.
If your culinary garlic life is still stressing you out, don’t forget about your freezer. If you’ve got too much fresh or granulated garlic to your name, go ahead and stash some in your freezer for when you’ve used all your room temperature goodies. You can even peel and mince ahead of time, and throw your prepped garlic into the fridge for a lazy day. Now, go forth with your newfound garlic knowledge, and please, for the sake of us all, don’t forget to brush your teeth.
*Yes, you can buy pre-peeled cloves or minced garlic in oil, but anyone will tell you, it’s not the same. If you’re going to cook with fresh garlic, buy a whole bulb and go from there.