Winter Herb Care

It’s been a very warm week in Raleigh, but looking ahead on the weather forecast, there will be a big dip in the evening low at the beginning of next week, almost to freezing. For my garden, I know this means it won’t be long before I bid farewell to the huge, bushy basil plants and some of the more tender perennials in the garden. I will make a final harvest of basil for a batch of pesto and wait for the blossoms to dry out so I can harvest the seeds for next summer’s crop. I’m located in Piedmont North Carolina, Zone 7b – 8a, which means our first frost should be coming up in the next several weeks.

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.

1. 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.
2. 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.
3. 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.
4. 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!

For the gardener who grows herbs in pots – potted plants are more vulnerable to extreme temperatures because the roots are not protected by the ground, which absorbs and stores heat from the sun (radiant energy!) for the roots on cool days and keeps them cool in the heat. Potted herbs should be brought indoors to the sunniest location you can find before temperatures drop to near freezing. The other option for perennials, if you want to keep them outdoors, is to recess the pots into the ground and then mulch on top of them. I use this method with mint as a way to keep it from overtaking the garden. Just remember that annuals will go to seed indoors or out IF you don’t manage to kill them first.