I wanted to pass along my experience that it appears that the beautiful Tweedia caerulea (alias Oxypetalum) has some degree of toxicity to other plants . . . at least, to Marigolds (Tagetes). I have two large flower beds roughly triangular in shape. A decorative low fence is along two sides of each triangle, and adjacent to the fence I planted Tweedia two years ago (they're perennial here), with the remainder of the beds varying from season to season. Last Winter/Spring, it was Sweet Williams; in due course, these were replaced by Tagetes 'Mumsy Yellow' and 'Mumsy Orange'. While the bulk of the Marigolds thrived, the row which was adjacent to the line of Tweedia plants was clearly stunted in both beds; and indeed the unfortunate Marigold which was in the corner at which the two lines of Tweedia converged in each bed died, alas. Adjacent to the line of Tweedia on the other side of the fence are masses of Pachyphytum and Sedum, neither of which seems affected by the proximity of the Tweedia (but, then, succulents are always pretty tough customers!). And so--those who might want to create a flower bed including Tweedia mixed with other plants will want to experiment with what will or will not be affected by Tweedia (the Sweet Williams were as happy as could be). I'd be interested in hearing if anyone else has had this experience with Tweedia.
