Bees on comfrey. There are lots of big stands of this robust perennial growing in many places near me – right outside my front door for one! – and the bumblebees absolutely love it. They often chew a hole in the top of the flower to access the nectaries and I do find that these plants don’t have many viable seed. They are collecting pollen too though so there must be some cross-pollination occurring.
Some might argue that it is too thuggish for a border but I happen to love it (even if the postman struggles to get through).
I am letting the comfrey grow up in my new chicken enclosure too as hens seem to enjoy the rather prickly leaves, as well as the nettles: both are really nutritious.