This may be wrong for you. But one of our inspectors told me about one year there was clover on both sides of a long drive and the bees never touched it. They decided to experiment and added lime to one side and leave the other side as it was. No time frame was given, but he said when he came back the side they limed was covered in bees and the other side was still bee free. I guess they just need to sweeten the pot, so to speak.