Comfrey also requires high amounts of water, so I don't really grow it myself. I use what's already growing around me for making fermented plant juices/extracts.
Consider this--we already know that in each area of the plant there are particular hormones, as well as nutrients. So, for a flowering tea, consider using flowers. I've gotten a rhodendron that doesn't like to bloom where it is to bloom by making a tea of spent Camellia blossoms.
As I mentioned before, comfrey won't grow well where I am without adding a LOT of water, which makes zero sense to me in any context. So, what is growing around me? Various oxalis species, woolly mullein, various thistles. So I use those.