Overwintering Potted Herbs Indoors

Know which herbs come inside, and when

Not every herb wants the same treatment. Tender herbs like Sweet Genovese Basil can't handle temperatures below 50°F and will blacken at the first chill, so bring them in early, when nights start dipping toward 50 to 55°F. Rosemary, Thyme, Spearmint, and Parsley are hardier and can stay outside until the first hard frost, roughly 32°F, but moving them in a week or two before that gives them time to adjust.

In the Pacific Northwest that usually means mid-October, but check your local forecast rather than the calendar. Perennial herbs such as English Thyme and Spearmint are also happy spending winter dormant in a sheltered spot outdoors if you don't have the window space, so bringing them in is a choice, not a requirement. Rosemary 'Tuscan Blue' is the one we most often encourage people to bring inside in colder climates, since it struggles when temperatures fall below 15 to 20°F.

Prepare plants before the move

A plant that goes straight from an outdoor patio to a warm living room can drop leaves from shock. Harden them off gradually over about a week: bring them into a sheltered porch or garage at night, then into a bright, cool indoor room, before settling them in their final spot.

Check every plant for pests first. Look under leaves and along stems for aphids, spider mites, and whiteflies, and rinse the foliage with a gentle spray of lukewarm water. Trim back leggy growth by about a third, and remove dead or yellowing stems. Then scoop the top inch of old soil and replace it with fresh mix, or repot into a clean container if roots are crowding the pot. Bringing a pest indoors with your herbs is how one plant becomes a dozen infested ones by January.

Light is the deciding factor

Herbs are sun lovers, and winter light is the biggest challenge. Most need 6 to 8 hours of bright light a day, which is more than even a south-facing window delivers in December. Place them directly in front of your sunniest window, ideally south or west, and keep leaves from touching cold glass on freezing nights.

If the window isn't enough, a full-spectrum LED grow light positioned 6 to 12 inches above the plants and running 12 to 14 hours a day will fill the gap. A cheap outlet timer takes the effort out of it. Rotate pots a quarter turn every week so all sides get exposure, and expect slower growth than in summer. Basil in particular becomes leggy and pale with too little light, so pinch it back often to keep it bushy.

Water and humidity indoors

Overwatering kills more indoor herbs than anything else. Mediterranean herbs like Rosemary and Thyme want the soil to dry out between waterings, roughly every 10 to 14 days in winter, checking that the top 2 inches are dry. Basil, Parsley, and Spearmint prefer more consistent moisture, closer to every 4 to 6 days, but never soggy.

Always use pots with drainage and empty saucers after 30 minutes. Heated indoor air is dry, often below 30 percent humidity, which invites spider mites on Rosemary. Group your pots together, set them on a pebble tray with water below the pot line, or run a small humidifier nearby. Keep herbs away from radiators and vents, aiming for daytime temperatures of 60 to 70°F and a slight nighttime drop to 55 to 60°F.

Feeding, harvesting, and the spring return

Growth slows in winter, so cut back on fertilizer. A diluted liquid feed, such as our Liquid Seaweed Plant Food at half strength, once every 4 to 6 weeks is enough. Harvest lightly and often: never take more than a third of a plant at once, and always cut just above a leaf pair so it branches. Regular pinching keeps herbs compact and delays flowering.

As days lengthen in March, increase watering and light gradually and give plants a fresh feed. When nighttime temperatures stay reliably above 50°F, usually in mid-May, harden them off again and move them back outside. Any that got scraggly can be cut back hard and repotted into a container a size larger. A simple stacking planter is also a nice way to keep several herbs together near your brightest window all season.