I hope I'm not stating the obvious, but Bigelow markets chamomile tea under the name "Cozy Chamomile" with the sole ingredient being chamomile flowers. I've bought it at Wal-Mart. Try www.bigelowtea.com for info. Don't know if this is what you're looking for. The gardener at the Alabama Wildlife Federation HQ grounds uses it regularly. I don't know the strength. I'll give her a call, if someone else doesn't answer your questions.
McGee & Stuckey write in " The Bountiful Container," brew up a batch of chamomile tea and water the seedlings with it." They don't address weakening the brew, but they do suggest it's best to water the seedlings from the bottom, as a general practice. Hope this helps. The chamomile tea may help minimize damping off, and it is organic.
Yes, actually it's the petals of the flowers. And by the way, chamomile also grows great in containers in case you are short on space.
I used to go harvest the common chamomile, it springs up around here like a weed. (Matter of fact, some folks refer to it as such.)
Chamomile brewed with a couple rose hips makes a great tea. Not that I drink tea very often but when I do it is usually in the Winter, most likely cus I am brewing it with summer ingredients and love it!