The herbs that we enjoy in the kitchen are both annuals and perennials. Basil and cilantro are annuals while sage and thyme are hardy perennials. There are also some herbs that we enjoy that need to be protected from frost and cold temperatures. Rosemary, lemon grass and lemon verbena are all perennial herbs but they cannot survive winter temperatures that are common in the Midwest and much of the continent. Rosemary , which is perhaps the hardiest of the tender perennial herbs, will usually survive a zone 6 winter with protection but is unlikely to survive even there if the temperatures drop into the middle teens for more than a night or two.
Bringing these herbs indoors for winter is not difficult but does require some thought and preparation.
Timing: For plants like rosemary, that are green all year long, you will want to wait until the average overnight temperatures are consistently hitting the mid to low 30Õs. For lemon grass and other herb grasses you can wait until the top growth is starting to turn brown. Other herbs such as lemon verbena and pineapple sage cannot take even light frost without some damage and should be potted up before a freeze occurs. If you find that you have left the plants too late, but temperatures have not dropped below 30 degrees, you can still save the plant by digging up the roots and letting it re-grow from there.
Digging: Dig the plant up including as many of the roots as possible. Taking a generous amount of surrounding soil will help you avoid cutting vital roots off. Shake any excess soil off the root and repot into a container with fresh potting mix.
Trim: Grasses and many other tender herbs can become large in just one season. Finding room for all these full size plants in your house can be a problem. Assuming your plant does not have flowers on Ð pineapple sage blooms very late Ð you can trim the growth to a manageable size.
Location: All plants need sunlight and winter sun is at a premium for most people, but put the plants in a location where it can get as much sun as possible. For rosemary, which can take a slightly lower temperature than tropical herbs, you can leave the potted plant in a sunny, sheltered position outside until the temperatures start to drop into the upper 20s. These extra few days outside allow the plant to adjust to the container, and the benefits of natural sunlight and breeze is beneficial.
For long term indoor storage, a cool bedroom or dining room is better for the plant than your moist kitchen. Most herbs will stay dormant in a cool room making them much easier to care for. Return the herbs to a sunny, warm room late next winter to bring the plant out of dormancy and ready for another season.
Bringing tender herbs indoors can be a fun way to keep your green thumb working, as well as save you some money on what you need to buy for next year.