A: Last year, the weather is your likely explanation, especially if you had your sprinkler on last fall. Rosemary, like many other herbs like oregano and thyme, likes to be in a drier soil, and won’t thrive in a constantly wet soil. Last September and October had a combined total of nearly thirty inches of rain, not far off of our yearly rainfall average, so your plants likely just couldn’t tolerate that much moisture where they were planted.
To do better this year, plant your dry-loving herbs like rosemary in a raised garden, which will encourage the soil to drain, and don’t water quite as much. If we have rain hit as hard as it did last year again, make sure to manually turn your sprinklers off throughout the yard until you actually need to water once more.