http://blog.eckraus.com/brew-your-own-herb-beers
When thinking about how to use herbs in homemade beer, add them in the same way as we do hops. These herbs may be added early or late in boil (depending on whether you’re looking for more bitterness, flavor, or aroma) or to the secondary fermenter, just like with dry hopping. One thing to keep in mind when brewing beer with herbs is that the herbs tend to be more delicate than hops. Many of them don’t need to be boiled as long as hops in order to extract bitterness and flavor.
You can pick these herbs from your own garden, or buy them from the store. Many herbs are available as tea blends, the tea bags making it east and convenient to strain out the herbs.
When developing an herb beer recipe, think about what flavor characteristics work well with the base beer. The herbs should complement the style characteristics, rather then dominate them. (Consult the BJCP guidelines for style 21A for more detailed information.) If brewing a gruit, forgo the hops. Other base beer styles, such as pale aleand wit, can be given an interesting twist by incorporating herbs in addition to the hops.