Separation from the nail bed. Once your nail separates from its nail bed, for whatever reason, it will not reattach. Nails grow back slowly. It takes about 6 months for fingernails and up to 18 months for toenails to grow back attached to the nail bed.. The WebMD Answers Staff. This answer should not be considered medical advice... This answer should not be considered medical advice and should not take the place of a doctor’s visit.