Indoor plants, whether they are year-round houseplants or plants you brought inside to over-winter, face several challenges. Temperatures that fluctuate from daytime heat to evening chill, dry air, short days and limited light are less than ideal growing conditions.
Adjust Your Watering Routine
It may sound counter-intuitive, but indoor plants need less water during the winter. While it's true that winter air is drier, plants experience a slower rate of growth during the cold weather. Some even go completely dormant. Less water is needed to keep them hydrated and overdoing it can lead to root rot.
The soil on the surface will dry quickly, but that's not a good indicator that the plant needs water. Poke your finger into the soil and check to see if it is dry an inch or 2 below the surface. That's when it's time to pull out the watering can. And try to use water that is about the same temperature as the air, to avoid shocking the plant's roots.
While most plants need less water during winter, don't wait until the leaves drop or start to dry, before giving them a drink. Keep in mind that different plants have different water needs; that remains as true in winter as in summer. Drought tolerant cacti and other succulents might not need watering at all.
Low humidity is probably the biggest hurdle to overcome during winter. The humidity level in heated homes can drop to 10 - 20% in winter and plants prefer a level closer to 50%. If you have a humidifier in your home, move your plants to a spot where they will enjoy its benefits. If you do not have a humidifier, you're going to need to raise the humidity level by other means.
Start by clustering your plants in groups. Plants naturally release water through their leaves by transpiring and grouping them together will put that moisture to good use. If you have room in the bathroom or kitchen, these are the best rooms to congregate your plants, other than the one with the humidifier in it, because they accumulate the most moisture from showers and boiling water.
Another good option is the old trick of placing your plants on or near a tray of water. Just don't let the plants sit in the water. Raise the bottom of the pots above the water level by placing stones in the water (higher than the water level) and sitting the pots on the stones.
Misting tends to be better at making the gardener feel good than the plant. You may think you are giving your plants some relief, but it's only a temporary blast of moisture. You'd need to mist multiple times a day to really see any benefit since the heat will evaporate the moisture quickly. If you have only a couple of plants and you think you will be very conscientious about misting, give it a try. It's hard to over mist an indoor plant. During humid summers, misting plants can lead to fungal problems. That should not be a problem during winter. There is less moisture in the air, to begin with, and there is even less, once the heat clicks on.
Pay Attention to Temperature
Most plants, like people, are comfortable in daytime temperatures between 65 to 75 degrees F. and nighttime temps above 50 degrees F. To provide that for your plants, keep them away from both cold drafts and sources of heat, like radiators, ovens, fireplaces, and electronic devices. Fluctuations in temperature can kill houseplants just as easily as prolonged periods of heat or cold.
Follow the Sun
Not only is there less sunlight during winter, it comes in at a lower angle. You may need to relocate your houseplants to a brighter spot or even add supplemental light. A good spot would be a south or west facing window that remains sunny all day. Just don't move them so close to a frosty window that they are getting a draft.
Rotate the pots when you water them so that all sides of the plant get some sun and to keep the plants growing evenly, rather than stretching to reach the light.
Put Your Houseplants on a Diet
Since your plants are barely growing, they don't need any fertilizer. Feeding them now will just upset their natural cycle, so hold off until early spring. When you start to see signs of new growth, or the green of the existing leaves appears to perk up, resume fertilizing, to give them a boost for the growing season.
Give your houseplants the essentials to sustain them through winter, but don't fuss over them or kill them with kindness. Keep an eye out for early signs of problems, which can still include insect pests, even in winter. But wait until the growing season resumes, before you re-pot them or start taking cuttings. Consider winter an offseason for your houseplants and let them rest.