[Zigûr]

Originally Posted by Ardent

It's a pity we don't know much about Radagast because herblore was part of his expertise, and he was the Maiar sent to Middle Earth by the female Valar who sang the Ents and herbs into being. Perhaps he dwelled in Rhosgobel, in the eaves of Mirkwood, because that was where the rest of the Entwives were?

For a long time I thought it curious that Radagast is not mentioned by Treebeard given that he was a Maia of Yavanna, but Yavanna was the Vala of animals as well as plants. I've eventually gained the impression that the Maiar "people" of the various Valar did not necessarily partake of the whole domain of their particular Vala: hence Aiwendil-Radagast was seemingly only interested in the animal side of the Yavanna-aspect of Arda, and not the plant. In Morgoth's Ring (where would I be without "Myths Transformed"?) the Professor notes that Sauron saw Gandalf as "only a rather cleverer Radagast - cleverer, because it is more profitable (more productive of power) to become absorbed in the study of people than of animals." (p.397) This would further suggest to me that Radagast's primary interest was in animals, despite his Vala being also concerned with plants.
After all, Treebeard describes Gandalf as "the only wizard that really cares about trees." (LR p.455) Then again Treebeard does add that "I do not know the history of wizards" and in Letter 153 Professor Tolkien remarks of Treebeard that "there is quite a lot he does not know or understand. He does not know what 'wizards' are, or whence they came." (Letters p.190)
That being said, as was quoted some years ago in this thread Professor Tolkien does offer some explanation for the Entwives' disappearance in Letter 144: "I think that in fact the Entwives had disappeared for good, being destroyed with their gardens in the War of the Last Alliance when Sauron pursued a scorched earth policy and burned their land", although he does leave room for surivors: "some, of course, may have fled east or even have become enslaved." So there is the possibility for a remnant to have ended up, seemingly, in Nurn or in Rhûn - a potential but I daresay unintentional association with, say, Dorwinion could perhaps be interpolated from this "fled east" suggestion.
Of course he does make a point of saying in Letter 247 of the Ents that "the males were devoted to Oromë, but the Wives to Yavanna." So perhaps there is room for an Entwife-Radagast connection even if Radagast was primarily interested in animals. That being said I personally am rather resistant to much embellishment of Radagast's role: for my own part I tend to feel that Professor Tolkien wrote very little about him for a reason: because he considered him to have done very little, and to be rather insignificant for all his origin. I don't wish to digress but to me Radagast, although doubtless a "worthy wizard" in his own way, is very much representative of the fallibility of the Valar and their plans, even if in a very different way to Saruman.
Like Professor Tolkien I think it's nice to hope that the Entwives survived in some way, and I find the Ent/Entwife song to be very moving, but I think the Professor was wise to leave the matter ambiguous. That mystery, the sense of loss and the tiny hope of reunion and reconciliation which is so doggedly clung to is, in my view, more powerful and more valuable than him providing us with a hard and fast answer about what happened.