Rosemary is a tender perennial herb. While rosemary thrives in cool temperatures, it does not tolerate freezing in winter so must be protected in many areas of the country. In areas where it remains below freezing for much of winter, planting rosemary in pots is preferable to ensure survival. Rosemary is an evergreen, so leaves remain green year-round though the plant goes dormant in winter and stops all growth until spring. Winterize your rosemary plants in fall to ensure they remain healthy throughout winter and into spring.
Cut back bed-grown rosemary in fall after the first frost, leaving only 3 to 6 inches of the plant remaining. Use sharp, clean shears to trim.
Place a wire cage around the plant. Use a tomato cage or make your own by wrapping a cylinder of chicken wire around the rosemary.
Fill the cage with straw mulch or dead leaves. Mulching protects the rosemary from winter burn and helps maintain the soil temperature.
Water the rosemary during winter when the soil is dry and isn't frozen. Drought stress, even in winter, can damage the herb.
Bring potted rosemary in after the first frost in fall. Do not prune it back severely, though harvesting some leaves for drying or preserving is fine.
Place the rosemary in a cool place for at least two weeks. An unheated covered porch, garage or shed is sufficient as long as the rosemary receives bright light during this period.
Bring the rosemary into the home after the two-week period. Place it in a brightly lit window.
Water the rosemary when the top layer of soil dries out. Provide water until it drains from the bottom of the pot, then hold off on watering until the soil dries again.