Preparing Your Herb Garden for the Cold Months In Nebraska, the first frost typically arrives between mid-October and early November. This is 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 rosemary and lavender thrive in warmth and sunshine but dislike soggy roots and frigid air. In raised beds, a little extra fal