Your bulbs and herbs will thank you.
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Winter is coming—and unless you live in the South, that means temperatures low enough to kill many garden and houseplants. Some plants are damaged by any temperature below 45°F, and a “hard freeze” of 32°F or below overnight will kill most container plants. When you start raking up your leaves and preparing your lawn for winter, it’s time to bring your houseplants inside. Here’s how to make sure they have a healthy start in their winter home.
Tender tropical plants can be damaged by temperatures below 45°F, even if you haven’t had frost yet, so aim to bring your houseplants indoors before nighttime temperatures dip that low.
When bringing houseplants inside, your first priority is to make sure you’re not bringing any insects or disease in with them. Aphids, scale insects, and mealy bugs are especially likely to hitch a ride inside on houseplants. Don’t let them.
Look carefully at your plants’ leaves and stems for signs of insects, like small brown lumps or sticky, sappy areas, and remove any wilted, brown, or yellow leaves. Clemson University has a helpful guide to common houseplant pests, complete with pictures. Clemson also suggests that you quarantine your outdoor plants in a separate room from your other plants for six weeks.
If you see signs of insects, consider spraying your plants with insecticidal soap, a compound that kills soft-bodied insects with its wet spray. It’s extremely effective against aphids and scale when it is wet, and has little effect on humans or animals. It’s the most benign option if you need to spray plants that will be close to you and your pets. Some plants can be damaged by it, though, so check ahead of time to make sure you’re in the clear.
Once you’ve finished your plant inspection, put your plant in a bucket or tub, fill it with enough warm water to cover the soil by half an inch, and wait 15 minutes. This bath will drive out any ants, slugs, snails, or other pests that may be hiding under the root ball. Once the 15 minutes are up, you can drain your plant. It’s a good idea to give it a quick spray bath too, to knock dust and any lingering insects off the leaves. If you don’t have a hose, put your plants in the shower for a quick wash (make sure the water pressure doesn’t wash away their soil!)
If your plant looks gangly and “leggy,” or its roots are crawling out of the pot, it’s time to replant. You can safely trim back up to one-third of overgrown foliage on most plants to give your plant a neater shape, and remove any diseased or weak stems. Use potting soil, not garden dirt, in your containers. Garden dirt can become compacted in containers, making it hard for plants’ roots to grow.
Then, it’s time for the move. Clean your windows to make sure plants can make the most of the light, and seal up and drafts around your windows that could cause a chill. If you’ve had your plants in the full sun, put them in a semi-shaded spot for a week or two to help them adapt to the lower light levels inside the house. Note that plants can lose some leaves while they adapt to the light, temperature, and humidity inside your home, so don’t be alarmed.
The Missouri Botanic Garden offers helpful tips for overwintering specific species of houseplants, including African violets and philodendrons. And if you’d like more houseplants, a University of Vermont professor suggests taking cuttings of impatiens, begonias, geraniums, and coleus to grow new plants for your indoor garden.
There’s nothing cooking with fresh mint, thyme, chives or tarragon. You can keep the flavors of summer growing on your windowsill all winter with a few easy tricks.
If you’ve been growing your herbs in containers, you can simply move them inside in their pot, but they’ll do better if they have time to adjust to lower light levels first. Move your potted herbs out of the sun to a semi-shaded spot for a week or two before you bring them indoors.
If your herbs are planted in your garden, dig them up and shake the dirt off their roots. Plant them in potting soil in a pot that has holes in the bottom to drain excess water. There should be some room in the pot around the plant—a half-inch on all sides is plenty.
To repot your herbs for the winter, put in the bottom layer of potting soil, position your plant, and pour in the remaining potting soil so the plant is buried to the same level it was in the garden. Commercial potting soil can be very dry and fluffy in the bag, so after you’ve poured in the soil, press down slightly with your hand to make sure that it is firm enough for the plant to stand up. Water the plant thoroughly; you may need to add more soil after watering to keep the plant roots covered.
Move the potted herb into a semi-shaded spot for a week or two before you move it inside to give it time to adjust to its new pot and new light level, and don’t let the pot dry out completely. If your herbs wilt, you’ve been waiting much too long to water.
Indoor life can be tough on plants. They may need more light than comes through your window, or air that’s more humid to truly thrive, and some of them need warm nighttime temperatures. Mint, rosemary, thyme, lemon balm, tarragon, and bay are among herbs that do well with indirect light.
Classic window sill herbs that need a little more light include sage, basil, parsley, chives, lavender, and chamomile. For these herbs, consider using a supplemental plant light if your window gets less than 6 hours of sunlight per day (preferably from a south-facing window).
You can increase the humidity around your plants by putting the herb pots in a tray with a layer of pebbles in the bottom. When you water the plants, the excess water will drain into the tray, then evaporate gradually to increase the humidity around your herbs.
Most herbs need to be watered often enough to keep the soil moist, although marjoram, oregano, sage, bay, thyme do best when the soil surface dries between waterings. Rosemary is notoriously finicky about watering, and can’t survive having its soil dry completely. Try misting your rosemary regularly with a spray bottle to keep it happy in the cooler months.
Basil can be grown indoors, but don’t set your hopes on another round of pesto-making. Basil cannot tolerate night time temperatures below 50°F—and since it’s an annual, sooner or later it will flower, set seed, and die despite your tender care. Enjoy it while you can.
Some showy garden plants grow from bulbs that can’t survive winters in the soil. Unlike spring-blooming daffodils and tulips, the bulbs of dahlias, calla lilies, gladiolus, oxalis, tuberous begonias, tigridia, freesia, caladiums (elephant ears), and canna plants all need to be dug and stored dry above freezing to keep them alive until the next growing season.
Once the first frost has darkened the leaves, dig up your bulbs. Don’t wait! If the bulbs actually freeze, they’ll turn into mush and die. Cut the stems off 4 to 6 inches above the top of the bulb, and gently brush or wash off the dirt—unless you’re storing gladiolus bulbs, which shouldn’t be cleaned.
Then, leave the bulbs in a cool, dark place to dry where the temperature is consistently 60ºF to 70ºF. Different bulbs need different amounts of time to cure before you store them. Most tender bulbs only need to cure for one to three days, but freesia, gladiolus, oxalis, and tigridia need three weeks to cure.
Store your cured bulbs in shallow boxes filled with sand, vermiculite, or sawdust in a place where they can stay at about 50ºF all winter, like a basement or an unheated room. Freesia, gladiolus, oxalis, and tigridia do better at slightly lower temperatures, 35ºF to 45ºF.
When you’re done bringing your plants inside, don’t clean up your garden beds. Lots of butterflies and native bees overwinter in spent flower stalks and leaf litter, and if you rake and clean too early, you’ll destroy their homes. The Xerces Society recommends that you wait until after apple and pear trees have finished blooming in your area to clean up your garden’s fallen leaves.