If you listen to the professional chefs on television, you'll get the impression that a good cook only uses fresh herbs. And while fresh herbs add nice, bright flavors to dishes, they aren't always the best choice when cooking at home.
If you're not growing fresh herbs in your garden, in pots, or on your windowsill, then buying them at the grocery can be expensive. And after taking a pricey bunch home, many home cooks use a pinch and then let the rest go bad. And while there's no true substitution for fresh herbs, and they're simply irreplaceable in certain dishes, some dishes actually taste better with dried herbs.
When to Use Fresh Herbs
If you're making a raw dish like a salad tossed with fresh herbs, a tarragon or green goddess dressing, or a pasta salad with fresh basil, then fresh herbs can't be beat. Uncooked dried herbs tend to have a dusty taste, and are no substitution for chopped, fresh cilantro leaves in guacamole, or raw parsley added at the end of a cream sauce. They add a bright freshness that can't be replaced by dried herbs.
Certain herbs are always better fresh and lose their distinctive flavor when dried. Delicate, leafy herbs like parsley, tarragon, and chives are always superior when fresh, and should typically be avoided when dried since they don't add much flavor to a dish. They're also best when raw or cooked for just a few minutes.
When to Use Dried Herbs
If you're making a sauce, stew, or soup that will bubble away on the stove or in the oven for more than a few minutes, then dried herbs can add a nice flavor. After cooking a dish containing fresh herbs for 10 or 15 minutes, all of the volatile oils and esters cook away that make fresh herbs taste fresh. There's no point in spending extra money when dried herbs will have the same effect.
Some dried herbs have better flavor and are worth keeping in your pantry than others. Oregano, marjoram, thyme, rosemary, bay leaf, curry leaf, and fennel seed are all good dried. When using dried rosemary, be sure to chop the tough leaves before adding to a recipe. Note that dried herbs do lose their potency over time, and should be discarded after a year.
The general rule for swapping dried for fresh herbs is to use 1/3 of the amount called for in the recipe. If a recipe calls for 1 tablespoon fresh rosemary, then add 1 teaspoon dried rosemary (there are 3 teaspoons in a tablespoon). The same rule applies with the reverse: if a recipe calls for 1 teaspoon of dried parsley, add 1 tablespoon fresh.
Remember that fresh herbs are best added at the end of cooking or after cooking. Dried herbs, on the other hand, benefit from some cooking, and should be added earlier to better develop their flavor.