I follow Pete Devaris's instructions and use a quart of Sitka spruce tips for 60 minutes. You get plenty of aroma and flavor that way, at least in beers like amber and wit. Taste them as you pick them and don't use any that taste nasty - according to Pete it varies from tree to tree, sometimes drastically. I've noticed the same thing, but nothing very drastic with the Doug firs around here.
Also, Sitka spruce tips are more citrusy than "evergreen", if by evergreen you mean piney. Try some Alaskan Winter if you can find any where you are, they use Sitka spruce.
Oh, and Pete recommends measuring by volume rather than weight, it is more consistent that way since moisture content can vary a lot based on the weather.