Dead herbs are a Farming plant that appears after a growing herb in a herb patch becomes diseased and then dies. There are 3 possible stages when herbs can die, and all herbs share the same model for the dead versions. Dead herbs can be avoided by using a plant cure on the diseased herb, or by casting Cure Plant from the Lunar spellbook.
Dead herbs can be restored using the Resurrect Crops spell on the Arceuus spellbook. If successful, this will restore the herb to its associated healthy growing stage, or else the patch will be automatically cleared. If the resurrected patch dies a second time, the spell will not work again.