There are several categories of herbs when discussing cold and frost tolerance, and a great resource is "Winterizing the Herb Garden" by the NCSU Department of Horticulture.
- First, we have evergreen perennials, which include rosemary, sage, thyme, and lavender. These like some mulch for the winter. A really hard freeze will still damage these, but I have yet to lose a plant due to winter temps. The best advice I have is to not do any serious pruning at the end of the fall, which can leave the plants vulnerable.
- Second, there are perennials that go dormant in the winter. These include oregano, Texas tarragon, mint, lemon verbena, and chives. Sometimes the garlic and onions will lose their foliage as well, although the garlic seems a bit hardier. These all benefit from a light mulching.
- Third, there are some annuals and biennials that will overwinter, meaning that with appropriate mulching and a milder winter, they might make it to spring before putting out new growth and going to seed. These include cilantro and parsley.
- Fourth, there are annuals that need to be harvested before temps drop too low. These include basil, dill, lemon grass, cilantro and parsley. Yes, the last two are in both category 3 and 4, but that is the nature of being in a zone where you never know what winter will bring!