Always use fresh if you can. Nothing beats the taste impact of fresh herbs and spices. If you do not have fresh, you can use dried however, you must divide by 3.
The recipes contained on this site always assume fresh. If the recipe calls for a tablespoon of fresh thyme for example, and you only have dried thyme, divide the volume by 3. So, instead of a tablespoon of fresh thyme you would use a teaspoon of dried thyme in the example. (Yes my friends, math matters.)
Lastly, spices and herbs have a FLAVOR shelf life though most home cooks seem to ignore that. We have been in friends and family kitchens cooking, and open up their spice cabinet to find items several years old. We suggest you only utilize spices and herbs dated within the last 6 months. Some people advise you to assume a 1 to 4 year shelf life but they are wrong!
You see, eating something that will not kill you, versus eating something the tastes great, are very different things. It’s just chemistry. Oxygen significantly affects the flavor of ground spices and herbs over time. In fact, great chefs only use fresh herbs and spices and never use ground spices over 3 months old. Go to your spice drawer right now and simply smell those ground spices and herbs over 6 months old. You should, if you are any kind of decent cook, be able to realize how their potency has been reduced.
We’ve tasted and tested the differences. We suggest 6 months should be your maximum time limit for throwing out the old ground stuff, though the following link we’ve included from BonAppetit goes even further to suggest 3 months is the maximum. Either buy fresh, buy whole spices (and use a grinder) since whole spices will last longer, or buy small quantities of ground spices knowing that you will throw out whatever is leftover after 6 months.
Remember, there are hundreds of things you can eat which won’t kill but do you really want to eat them? That’s exactly the issue with stupid advice suggesting spice shelf life is as much as 4 years. FLAVOR IS THE ISSUE!