I have had trouble in past seasons with bidens and bought it again this year. It always looks pathetic after about 10 days after bringing it home from a premium nursery. What am I doing wrong and do you have any suggestions to help bring it back from a very sad state?
It may be too crowded in the planter to get as much sun as it wants. Remove the dead stems and trim back any lengthy stems by 1/3 and it should bounce back. It does fine with soil on the dry side. If it is in a container with plants that like moist soil, then I would remove it and plant it elsewhere, in full sun. I also would give it about half the recommended amount of fertilizer as too much nitrogen will favor leafy growth over blooms. There is plenty of time left in summer to enjoy your Bidens.