When to Start Prepping Herb Beds for Winter In Nebraska, the first frost usually arrives between mid-October and early November. That’s your cue to begin preparing perennial herbs like rosemary and lavender for the cold months ahead. Once temperatures dip below 40°F at night, it’s time to trim, tidy, and preserve what’s left of the harvest. Both of these Mediterranean herbs thrive in warmth and sunshine but dislike soggy roots and frigid air. In raised beds, that means a litt