I've had chamomile flowers blooming in my garden for several years now.
(I don't remember when or where I originally got the plant - but it reappears every year!)
This year I decided to harvest some to see how they taste as tea... I found an online website with instructions on how to dry chamomile flowers.
Some looked as if they had almost finished blooming, so I left them on the stems. If I remove all the flowers, will the plant stop self-seeding, I wondered...
Apparently they can be frozen as well... Tea can be made from fresh flowers as well, according to another article on the same DIY herbal tea site.