Winter Care of Herb Plants

Tom Wajda
Adams County Master Gardener

First things first: Before bringing plants indoors it is important to properly prepare them. Plants that have been in the ground need to be dug up and potted. Plants already in pots need to be checked to see if they are root bound. If they are, you will want to repot them. Wash the soil off the roots and prune any broken or oversized ones. You should also prune the branches taking special care to open up the middle of the plant to allow good air circulation and let in light. As a rule of thumb both the roots and branches should be cut back by about one third.

Get rid of insects: Most insecticides kill only adult insects – not larva or eggs. In order to insure that you’ve gotten them all, spray your plants every 5 days for two weeks before bringing them indoors. Take care of insects in the soil by using a rotenone drench.

Water it when it’s dry: Many professional growers claim that more indoor plants are killed by over watering then under watering. This is certainly the case with most herbs; they simply do not like wet feet. So water them when they are dry – usually not more than once a week. And – this is important – don’t let the pots sit in saucers full of water. About an hour after you water your plants, empty those saucers and let the roots breath.

Bay: Bay is one of the easiest plants to winter over indoors. It likes a sunny window and has few problems with insects or disease although it sometimes suffers from scale. If you notice scale, scrape off the waxy bumps and spray with a good insecticide.

Lavender: The tender lavenders (French, Fringed, Spanish, and Dentata) all need to come indoors for the winter. Happily, they are usually quite prolific bloomers. Trim them to a nice shape, feed with a balanced fertilizer, and give them as much light as possible. They will reward you with blossoms in about six weeks.

Lemon Verbena: Lemon verbena is a deciduous plant – it will lose its leaves no matter what you do. Without leaves, it needs less water so be careful not to give it too much. It will do quite well in an east or west window. In mid-February, just when you are ready to throw it out, new growth will appear. Move it to better light and keep an eye out for red spider mites.

Rosemary: Rosemary is a beautiful and impressive plant indoors. However, it can sometimes be difficult. Start by thinning out the plant to let light into the center of the plant and allow good air circulation. (Most plants indoors benefit from moving air. If you can, place a small fan near them.) Rosemary wants all the light it can get, so be sure to put it in a south window. Do not over water! (Most rosemary is hardy down to 15 or 20 degrees. This means that in much of the country rosemary can stay outdoors until early December and can be moved out of the house in early March.)

Scented Geraniums: Scented geraniums (pelargaoniums) are a fascinating family of plants. Most gardeners are aware of the rose variety, but there are more than 100 other types each with its own distinctive aroma or leaf shape or coloration. These plants tend to get leggy during the winter so trim them quite severely in the fall and touch them up every month or so. The scented geraniums will tolerate low light situations during the winter and prefer a cool room. Water them sparingly. Aphids can be a problem; inspect your plants regularly; if you find any insects spray every five days for two weeks to control adults, larvae, and eggs.

Perennial Herbs Outdoors

Most perennial herbs are quite hardy and will survive reasonably well outdoors even if temperatures go to zero or below. However, if they are subjected to very cold nights (below 10 degrees) and dry winds they may have trouble surviving unless they are mulched. (By the way, a foot of snow makes a great mulch. If you live in a snowy area your herbs are likely to survive nicely even if you do nothing.)

For those of us who face the likelihood of cold nights in January and February with little or no snow cover, mulching with straw or leaves is in order. Two or three inches of mulch will protect most plants. Taller species, e.g., lavender,, sage and rue, should be covered more deeply. Branches cut off your Christmas tree are useful to protect taller plants. (It also makes it easier to get the tree out of the house.) Do not mulch too early in the winter as the field mice will likely try to make their homes under the mulch. Wait until the ground begins to freeze; the mice will have already found homes elsewhere.

Herbs that die back to the ground (chives, tarragon, oregano, mint, etc.) do not require mulching. Most of the plants that die back require 6-8 weeks of freezing weather in order to prepare for next year’s growth. You can take advantage of this by potting up some of these plants, then burying the pots level with the ground. Dig them up in mid-January, let them thaw, them place them in a sunny window or under plant lights. Water and feed regularly. In 4-6 weeks you should have fresh herbs for your kitchen.

Read other articles on growing herbs or vegetables

Read other gardening articles by Tom Wajda