11 Winter Houseplant Care Tips for Dark, Dry Months

Iowa State Extension notes that spots more than a few feet from even a bright window get too little light for most houseplants. In winter that matters more, because the light coming through the glass is weaker. Move plants from the back of the room to the sill or a table right beside the window. A south or west window gives the most winter light in most homes. Pull blinds fully open during the day and clean the glass, since winter grime cuts light too. Watch the new leaves: small, pale leaves and long gaps on the stem mean the plant still wants more light.

Closer to the window is good, but leaves touching icy glass can get cold damage. Clemson HGIC warns against placing plants "too close to windows, where they might suffer cold damage." No extension page we read gives an exact gap, so use a simple check: put your hand flat on the glass on a cold morning. If it feels icy, keep leaves from touching it. On freezing nights, slide pots back from the window or close a curtain between the plants and the glass, then return them in the morning.

If your windows face north or the room is dark, a grow light makes up the difference. The NC State Extension Gardener Handbook says a fluorescent fixture is typically placed about 12 inches above plants, and an average houseplant needs light for about 12 hours a day. It also says plants should not be lit 24 hours a day. LED clip-on lights vary in strength, so follow the maker's distance guide and use a plug-in timer so the light runs the same hours every day. A small clip-on light is enough for one to three plants on a desk or shelf.

Iowa State Extension says it is time to water when the soil is dry to the touch about an inch down. Clemson HGIC gives the same test in a different form: push a finger into the mix up to the first joint, and water if it feels dry at the fingertip. Clemson also says there's no pat answer to how often, because it depends on the plant, pot, mix and room. Here's the winter twist. NC State says plants need less water in winter because growth slows. Clemson's January notes say plants can dry out faster once the heat is on. Both can be true in the same house, which is why the finger test beats a calendar.

Clemson HGIC recommends water between 62 and 72°F for indoor plants. In winter, cold tap water can be well below that. An easy fix is to fill your watering can the night before and leave it on the counter, so it warms to room temperature by morning. Clemson also advises against using softened water on houseplants. If you have a water softener, use water from a tap before the softener or use rainwater or bottled water.

You can't fix humidity you haven't measured. A small digital hygrometer costs little and shows the humidity in the room where your plants live. Set it among the plants, not next to a heater or a humidifier, and check it at different times of day for a week. If it reads below 40 percent, the plants are below Iowa State's target range. Most also show temperature, which lets you check that the room stays in the 65 to 75°F range Iowa State suggests for most indoor plants.

Iowa State suggests two low-cost ways to add humidity. First, group plants together, since water evaporating from the soil and leaves raises the humidity around them. Second, set pots on trays or saucers filled with pebbles and water. Iowa State says to keep the water level below the bottoms of the pots, so the roots don't sit in water. And skip the mister. Iowa State says misting is not an effective way to raise humidity, since it would have to be done several times a day to help.

For a real jump in humidity, Iowa State calls humidifiers an excellent way to raise it. Clemson HGIC suggests grouping humidity-loving plants together and adding a humidifier to that space. A small humidifier near a plant cluster is more efficient than trying to humidify a whole home. Check your hygrometer after a few days and aim for the 40 to 50 percent range. Clean the humidifier as the maker directs, since standing water in the tank can grow mold and bacteria.

Heat registers and open doors are the two drafts Iowa State warns about. The NC State handbook says to keep containers away from cold drafts from outside doors and from the drying air of heating ducts. Clemson HGIC says plants can dry out when heaters are on and should be "far from vents or fireplaces." None of these sources gives an exact distance, so use the hand test again. If you can feel warm air blowing or a cold draft where the plant sits, move it. Watch the windowsill above a radiator too. It can be hot by day and cold at night.

Iowa State Extension says to stop fertilizing in fall and winter, because plants aren't actively growing. The NC State handbook is more exact: fertilize indoor houseplants once a month from March to October, and not from November to February unless deficiency symptoms appear. Extra fertilizer in winter can build up as salts in the soil when the plant isn't using it. One older Iowa State care page extends feeding into November or December, but its newer fall guidance says to stop. Put the plant food away now and bring it back out when you see new growth in spring.

Dust on leaves blocks some of the light that is already in short supply. The NC State handbook suggests washing leaves every two or three months. Wipe large leaves with a soft damp cloth, supporting each leaf from below, or rinse smaller plants in the shower with lukewarm water. While you clean, check the undersides. NC State notes that spider mites prefer dry conditions, so heated winter air suits them. Fine webbing, tiny specks and stippled, dull leaves are the signs. If you bring in new plants, Iowa State suggests keeping them apart from other houseplants for 3 to 4 weeks.