Come On In: Tips for Overwintering Plants Indoors

Instead of transplanting tomatoes, take a cutting and put it in water until it can be transplanted to an inside pot. johan kusuma/Shutterstock

Bring the basil, rosemary, lemongrass, tomatoes, peppers, and even dwarf citrus trees indoors for a winter bounty and a head start on next season.

Looking over the garden as the days get shorter and the first frost moves closer signals the end of the growing season for those without a greenhouse—or does it?

For those with the space and commitment, overwintering indoors offers several benefits ranging from larger plants with robust root systems to plant out in the spring, to saving cuttings of plants that don’t provide viable seeds, such as Sissoo/Brazilian spinach, or a cutting of one’s favorite basil to create a tasty clone. Plus, few things are more delightful than adding fresh-picked mint to hot chocolate while snuggled inside, gazing out the window at fresh snowfall. Overwintering can even be taken a step further, with an area set aside to grow freshly seeded greens.

The Big Move

Choose the healthiest, most robust plants to bring indoors, and plan to bring them in before the first frost. If it’s growing in a container, just bring it indoors when ready. If not, dig up the plant carefully, making sure to take a nice root ball. Shake off some of the garden soil, fill a container with potting mix, and place the plant at the same level at which it was growing in the garden.

Why potting mix? Garden soil is heavy and can suffocate container plants. This is also a good time to give the plant a “haircut,” trimming it for bushier growth or to remove sections damaged while transplanting. Inspect the plant for bugs, and treat accordingly. Even if everything looks good, it’s a good idea to give the soil a pest-removing soak as well by applying 3 tablespoons of soap to one gallon of water. Soak the plant for 15 minutes, spraying the leaves at the same time. Rinse well.

While bushy plants such as peppers can be transplanted full grown, tomatoes don’t do as well. Instead, take a cutting—or a few, in case they all don’t make it—from a sturdy 6-inch or longer sucker (a shoot growing between the main stem and a branch). Cut it just below a node (where the leaf joins the stem) and put it in water. Rooting hormone will speed the process but isn’t a requirement. Set it in a bright area but out of direct sunlight. Once it starts to get roots, transplant it into a container filled with potting mix.

Herbs grow well indoors if placed near a bright window. New Africa/Shutterstock

Climate Control

Once the garden plants move indoors, they’re exactly that—indoor plants—and should be treated accordingly. Lessen watering. Touch the top of the soil; if it’s dry, it’s time to water. Don’t fertilize until (if/when) they show new growth, and then apply a light amount of fertilizer monthly. Most houses are too dry for the average plant; one easy solution is to set the pots in a shallow tray filled with water and pebbles to increase humidity.

Situate the “garden” in or adjacent to a sunny window, or add supplemental grow lights if needed; they’re a one-time, very worthwhile investment as plants that have to stretch toward the light will soon become weak and leggy. There’s a reason that many cooks, even those without gardens, grow basil, cilantro, parsley, chervil, rosemary, bay laurel, mint, chives, oregano, thyme, sage, and lemongrass in a sunny spot; most can make do with a mere four hours of sunlight per day (although they do prefer six to eight hours, if available). Also, be sure to keep the plants away from cold drafts, radiators, and hot air vents, all of which can dry and otherwise stress them.

Harvest Versus Stasis

In addition to growing herbs on a windowsill, dwarf tomatoes and compact peppers, as well as radishes, carrots, scallions, and mushrooms can all be grown successfully indoors during winter, providing a small yet delicious harvest. Ginger can be grown, too, although it needs a lot of humidity, so keep the spray bottle handy. Certain types of lettuce, such as Tom Thumb, baby oakleaf, black-seeded Simpson, Swiss chard, spinach, and kale will also thrive in a pot placed in direct sunlight and kept at a comfortable 65 to 80 degrees Fahrenheit. Overwintering citrus trees has a long and grand history.

For many gardeners and plants alike, the shorter days, reduced sunlight, and cooler temperatures are the cues to kick back and hibernate until spring. The solution is to keep fruits, vegetable plants, as well as perennial flowers, etc., in stasis—where they’re alive and well but not doing much active growing. This is easily accomplished if one has an unheated garage, with temperatures between 45 and 60 degrees (or 35 to 45 degrees for bare-rooted geraniums). While the plants are dormant, ambient winter light should be enough for most, or better yet, place them under a grow light on a timer set to a shortened day. Now kick back and enjoy the fun of flipping through next year’s garden catalogs.

Ginger can be grown indoors if provided enough humidity. Jackie Gump/Shutterstock

Common Mistakes

Protecting tender plants during the harsh months of winter is about balance. It’s all about keeping the plants content.

Overwatering

Proper hydration is critical when it comes to plants that have gone semidormant, as overwatering can quickly lead to root rot. When in doubt, let the soil dry out for a day or two unless the plant is looking wilted or withered.

Poor Ventilation

While hibernating plants can be quite content in a corner of an unheated garage, that doesn’t mean that they don’t need their space. Make sure that they receive adequate airflow around and between them to prevent fungus and mold development.

Dark and Dry

When it comes to winter sun, south- or west-facing windows work best; if those aren’t available, use grow lights. Humidity matters, as well. Plants such as ginger and the lovely hanging porch plant pothos will thrive in a bathroom where the family frequently showers.