Do I need to leave the plants growing until the seeds turn brown? or can I pull up the plants now and dry them?
Green seeds for coriander have a different, very powerful flavor, and are used in some Indian cooking. Most often, they are left on the plant until the seeds are brown, and almost ready to open. The flavor then is nutty, warm,good for gingerbread and pastries. I put the stems/seeds in a brown bag to let them dry further and collect them. For using it as an herb, rub the hulls off of the seed. If you pick them green, it is more difficult to get the hull off. Try some green and some brown, see what you like.
