And while these guys won’t survive a cold winter outdoors, you can protect a favorite plant by bringing it inside for the winter and replanting it in the spring! Be sure to only bring in healthy plants, free of visible diseases and insect pests. If you have any doubts, opt for cuttings (more on that below), which are the easiest to inspect and least likely to harbor stowaways. For potted plants, check to make sure you don’t have, say, an ant colony in residence.
There are three easy ways to bring plants inside for winter:
Keep Them Potted
Perhaps the simplest way to manage tender perennials is to grow them in pots year-round, moving them outside in the late spring and back inside before frost in the fall. This is a good method for slow-growing woody herbs such as rosemary and lavender, as well as small ornamental hot pepper varieties. Faster-growing medium-sized perennials like stevia and tarragon also make good potted plants, but they tend to do better if you cut them back to about an inch above ground level before bringing them inside in the fall, and perhaps once or twice during the summer, especially if they have gotten tall and floppy (use, dry, or freeze the leaves you cut off).
Related: Freeze It, Dry It, Eat It Later
Dig Them Up + Pot Them
If you have small- to medium-sized plants growing in your garden, you may be able to dig them up, experiment with container gardening and plant them in large pots, cut them back by about half their height (unless they are really small), and bring them inside. Use a sharp shovel to cut around your chosen plant, aiming to create a ball of soil the size and shape of your pot with the plant in the center. Carefully slide the soil into the pot, shaving off more soil if it doesn’t fit. Fill any gaps with compost and water generously.
Cut Them, Root Them, Pot Them
Large plants with extensive root systems are difficult to dig up and transplant successfully, but many can be overwintered by cutting off the tips of shoots, encouraging them to sprout roots, and then planting the rooted cuttings in small pots. Cuttings take up a lot less space, so it’s a good method if you have only a little sunny space indoors. And if you want even more of a given plant, you can snip off the tips of the original cutting when they get tall enough during the winter and root those as well. Tomato, sweet potato, and many herb cuttings are easy to root.
Related: Enjoy Fresh Herbs All Year Long
Basil is not technically a perennial, but it roots easily, and rooted cuttings usually do better than older plants when it comes to providing some leaves during the winter. Plant rooted cuttings in a potting mix that holds water without getting soggy. Buy an organic potting soil, or blend equal parts of good garden soil, finished compost, and perlite or vermiculite.
There are two basic ways to take care of your tender perennials: Keep them actively growing, or allow them to go dormant. Knowing how much sunny indoor space you want to dedicate and what temperature the space maintains will help you decide what you want to do, as well as how many plants you can bring in.
Keeping Them Growing
If you have sunny windows or glass patio doors (or are willing to use grow lights) in spaces where daytime temperatures stay about 65 to 70 degrees and night temperatures are at least 10 degrees lower (the 50s are perfect), you can keep herbs happy and harvestable all winter. However, even with eight hours of winter sunlight, your plants may get a bit ratty and stretched-looking by spring.
You also have a good place to keep fruiting plants, such as tomatoes and peppers, alive. Alive doesn’t mean fruiting, however. Unless you want to maintain jungle-like conditions in your house (75 to 85 degrees during the day, with high humidity ), use grow lights to supplement the short days of winter, and move pollen around by hand each day to fertilize the flowers, these plants are unlikely to set more fruit indoors. Any green fruit already on the plant when you move it inside may keep growing and ripen, but don’t expect summer-flavor. But no matter how tired your overwintered plants look by spring they will almost surely perk up as the days get longer and start cranking out fruit once you plant them back in the garden, often long before new seedlings have even opened their first flowers.
Just like other houseplants your visiting perennials hate wet feet. Water when the top of the soil feels dry, or learn to judge the moisture in the soil by hefting the pot and watering only when it feels light. Plants grow more slowly as the sun drops lower in the sky and may need very little water in December and January, but by about Valentine’s Day, they will start picking up speed and will probably need to be watered more often and will appreciated some liquid organic fertilizer every couple of weeks.
Indoor heated air tends to be very dry and hard on plants, and they can make them more susceptible to insect pests. Using a humidifier can help. If insect pests appear, you can often hand pinch them, wash them off the plant in the shower, or, if those methods fail or aren’t practical, spray them with water with a few drops of liquid soap added or homemade DIY insect spray.
Related: This DIY Insect Spray Covers Most Pests
In the spring, as your average last-frost date approaches, start watching the weather. When the forecast looks as if nights will be staying above 50 for the foreseeable future, start getting your plants ready to move back outside by lowering the daytime temperature (if possible) and increasing the amount and intensity of sunlight they get over the course of a week or so as you would with any new plant. Carrying them outside and putting them in a sheltered and slightly sunnier place each morning and bringing them back inside in at night is best, but covering them at night outside will work, too.
Related: The Secrets to Successful Planting
Letting Them Go Dormant
If you don’t have the space or light to keep all the plants you want to preserve actively growing, many tender perennials can be potted, cut back to a manageable size (keep 6 to 12 inches of stem and branches for veggies like peppers), and kept in a very cool but above freezing place (about 55 degrees is ideal for peppers, and even cooler may work for many plants) such as a garage, unheated porch, or basement. For this method, light is not required. The plants will lose some or all of their leaves, and use very little water. Once a month may be plenty; but don’t let them get bone-dry either. A month or so before your frost-free date in the spring, move the plants somewhere they will get eight hours or more of sunlight, and they will wake up and start growing again. Not every plant stored this way will survive, but many will.