By Lori Rose
Some perennial herb plants, such as lavender, rosemary and thyme can survive the winter outdoors in our area. Here are a few tips to put them to bed for the winter, and help ensure they return to their full glory next spring: If you fertilize your herbs during the growing season, stop doing so in late August to prevent tender new growth that may succumb to frost. Keep plants well-watered during the heat of the summer and into the fall. Drought will stress the plants, making them more susceptible to damage from the cold. Then, after the first hard freeze, prune the plants down to about six inches tall and cover the soil around the roots with a few inches of mulch. Say goodnight to them, and look forward to seeing strong new growth on the plants next spring.
But, don’t you miss having fresh herbs in the winter? I know I do. Their scent and flavor would surely lift our spirits during the short winter days, when it seems like spring will never arrive. Why not try bringing some garden herbs indoors and keeping them as houseplants for the winter? They can even be harvested for cooking, drying or just enjoying their scent throughout the colder months. A bright window or grow lights on a timer will keep them, and you, happy over the dreary days of winter.
Some plants can cope with the short days of winter and dry indoor air better than others. Be aware of either hot or cold drafts, and of placing plants too close to radiators or hot air outlets. The plants may not look their best in February, but if you can hold out until the frost has passed, you can bring them back outside again for another season of flavor and scent.
The easiest herb plants to overwinter indoors are soft-stemmed herbs like basil and mint. Simply cut a stem about six inches long, remove the bottom leaves, and put them in a glass of water. Once roots form, pot them up in clean pots filled with commercial houseplant soil.
Although hardy herbs, like thyme, mint, oregano and chives should survive most winters outdoors in our area, especially if you follow the tips above, they are also very easy to overwinter indoors. Frost-sensitive herbs can also be dug up and repotted, including annuals like basil and chamomile, and tender perennial herbs like lemon verbena. Ifyou'd like to try growing some indoors over the winter, follow the directions below to dig some up and re-pot them.
In mid-fall, dig up a few stems of thyme, mint and oregano with roots attached. Dig up the entire plants of chives, basil, chamomile and lemon verbena, and try to keep the roots intact. Trim them a little, but cut no more than one-third off the top and/or sides of each plant. Gently remove as much garden soil as possible from the roots. Use a commercially prepared houseplant potting mix and clean pots. Garden soil will not drain as well and may contain weed seeds, insects and other pests. Window boxes are a space-saving way to bring a collection of herbs inside for the winter. Once the plants are potted up, water them well. Place them in a shady spot outside to recover for a day or two, and then put them back in the sun. Water them every day until you are ready to bring them indoors.
When night temperatures dip into the 40s, gradually reduce light levels by moving plants from sun to light shade to heavy shade over the course of one week. Then, inspect the plants carefully, removing any dead, damaged or diseased parts and any visible insects. Wash the leaves and stems and allow them to dry. Spray the entire plant (upper and lower surfaces of leaves) with Neem or insecticidal soap.
Before the first frost, re-spray them with Neem or insecticidal soap, and then submerge each pot in a bucket of water. That cleans the pot and makes any insects left in the soil float to the top. Keep these plants separated from other indoor plants for at least a few weeks in case pest problems develop.
No sunny window? No problem. Herb plants are more likely to grow compact and bushy indoors if you add grow lights to supplement any natural light they receive throughout the day. They will grow healthier and happier and provide you with more flavor and fragrance. If there isn't enough natural light in the house to grow light-loving herb plants.
Here’s an inexpensive step-by-step procedure for lighting indoor plants: Choose a sturdy shelf or table to hold potted plants. Line the shelf or table with bright white paper, aluminum foil, or a mirror to reflect the light. Place the potted plants on top. Hang a grow light twelve inches above the plants. Or, place desk lamps on the shelf or table and raise them over the plants with a stack of books if necessary. Put the lights on a timer to give the plants twelve to eighteen hours of light per day.
Some perennial herbs, like sage, may or may not make it through the winter outdoors. Follow the steps above to give sage the best chance of surviving the winter outdoors. Or, to bring sage indoors, propagate it from a cutting. First, select containers about four inches deep and fill them with moist (not overly wet) houseplant potting mix. Then, cut off shoot tips three or four inches long and remove the leaves on the lower part of the stem. Dip the cuttings in rooting hormone powder, and insert them into the potting mix about an inch and a half deep. Put the containers in clear plastic bags, twist-tie the tops closed and place the containers in a warm location that receives bright but indirect sun. Check the condensation on the plastic bags occasionally and open the tops of the bags now and then to release some excess moisture. Remove the plastic bags after about a week and keep the soil moist but not soggy. Other herbs that can be propagated and overwintered this way include thyme and oregano.
In the spring, wait until the danger of frost has passed before bringing over-wintered herbs back outside. Bring the pots outside and place them in the shade (no direct sun) for a few days, bringing them back inside at night. Then each day for about a week move them throughout the day to receive more and more sun each day. Keep them well-watered, do not let the pots dry out. They can be left outside overnight as long as the night temperatures are above 50 degrees F. Once the potted plants are adjusted to full sun, transplant them back into the garden. Keep them shaded and well-watered for a few days as they make the transition back to the outdoor garden.
Try overwintering some of your favorite perennial herbs indoors, like chives, thyme, rosemary, lavender, and pineapple sage, or tender herbs like basil, chamomile and lemon verbena. Have fun with them, and enjoy the beauty of growing plants for scent and flavor, even on the bleakest winter days.
Lori Rose, the Midnight Gardener, is a Temple University Certified Master Home Gardener and member of GardenComm: Garden Communicators International. She has gardened since childhood and has been writing about gardening for over twenty years.