How to Overwinter Herbs
Although herbs are relatively fuss-free plants, they need protection from frost, ice and snow. Here are a few simple ways to help them survive the winter.
Overwintering Woody Perennial Herbs
Bringing Potted Herbs Inside
Woody herbs like rosemary, lavender, sage, sweet bay and tarragon make fine houseplants in winter. Lemon verbena can also be overwintered indoors, although it will probably drop its leaves.
Whether you pot them before the first frosts of winter or simply move previously potted herbs indoors before cold weather sets in, be sure to give each of your herb plants a good washing before bringing them inside. Washing will remove not only dirt and debris, but it will also dislodge any pests and their eggs.
To wash herb plants, first mix up a solution of warm, soapy water, using a mild dishwashing liquid like Method or Palmolive.
Sponge the herb plants down with the sudsy water. (If the plants are relatively small and lightweight, you can simply dip them into the sink.) Then rinse the herbs well with cup fulls or sprays of clear water. Short, strong bursts are particularly effective for dislodging insect eggs.
In regions with harsh, icy winters, it's easiest to grow tender perennial herbs in pots year round. Herbs that are dug up in autumn, potted, overwintered indoors and then replanted outside year after year experience repeated stress due to root loss, which could stunt their growth or, in cases of extreme root loss, kill them.
What herbs do you grow?
To accommodate next year's growth, you can re-pot herbs before moving them inside, placing them in larger containers and adding fresh soil mixed with compost to assure good drainage.
Suddenly moving potted herbs indoors can cause them undue stress. It's best to acclimate them slowly to their new home.
First, prepare them for the move. If you fertilize them, stop feeding your potted herbs in early autumn. Also give them a good pruning.
Then place the herbs in a sheltered outdoor location, such as a covered porch, deck or breezeway, for one or two weeks before bringing them inside.
Winter Indoor Care
Once they're inside, place the potted herbs in a sunny location that receives at least six hours of sunlight per day. Recommence fertilizing, applying it every two weeks at the most. You may also prune your herb plants again if you like, snipping off up 1/3 growth.
Usually, woody herbs like rosemary like to be well watered when grown indoors, although they don't like soggy soil.
Lemon verbena is an exception and should be watered sparingly when overwintered indoors.
Overwintering Herbaceous Perennial Herbs
Chives can be overwintered by a combination of potting and mulching.
First, dig up clumps of them from your outdoor herb garden in late summer/early fall and pot them. Bury the pots to their rims and cover them with leaves or straw. Dig the pots up in late fall/early winter and then acclimate them to the indoors over a period of several weeks. You'll have lovely green chives for the New Year.
Protecting Herbaceous Herbs Outside
Common herbaceous perennial herbs include catnip, chives, fennel, lemon balm, lemongrass, mint, oregano and thyme. In climates where winters are harsh, herbaceous perennials will die down to the ground when hit by hard frosts and reemerge from their roots in spring.
Mulching herbaceous perennial herbs is an easy way to protect them from the frosts and thaws of winter. Straw is a good mulch choice. Unlike peat and pine bark, it will not acidify the soil as it breaks down.
Boughs from evergreen trees may also be placed over herbaceous perennial herbs to shelter them from frost, ice and snow—and it's a great way to recycle Christmas trees. The boughs, which will not decay very much over the winter, are easy to remove once the threat of frost has passed in spring.
Overwintering Annual Herbs
Common annual herbs include basil, borage, chervil, cilantro, dill, parsley and salvia.
Although annual herbs can't actually be overwintered, it is possible to grow them indoors from seeds. Basil is also fairly easy to grow from cuttings. Take the cuttings at the end of the growing season, before the first killing frost.
© 2012 Jill Spencer