When it comes to houseplants and the people who grow them, there’s not much to love about winter.
The days are short, cold and often gray, temperatures plunge during the long nights, and dry heat from furnaces and fireplaces sucks moisture from the air. In short, for three or four months of the year — or longer, depending on where you live — the indoor climate for houseplants is the polar opposite of the warm and moist conditions plants are genetically engineered to experience in their natural habitat.
There are ways, though, to show houseplants the love they need to survive and even thrive during these difficult growing months. The first is to be aware of the greatest dangers your houseplants face. Those dangers are "the classic combo of low light, low humidity and temperature extremes," said Becky Brinkman, manager of the Fuqua Orchid Center at the Atlanta Botanical Garden. "The remedy," she said, is the real estate mantra of "location, location, location — and some attention."
Another way to show houseplants some winter love is to avoid the three most common mistakes Brinkman says home growers make when caring for houseplants in winter:
- Leaving tropical plants on an unheated porch or garage or too close to a hot and dry air source.
- Putting them too far away from a direct source of natural light.
- Forgetting to check them for water.
To help you avoid these mistakes and to help them survive until longer periods of daylight, an increase in temperatures and a rise in humidity inevitably return in the spring, here are some do's and don'ts for winter houseplant care, courtesy of Brinkman and some members of the houseplant forum of the National Gardening Association.
The do list
Know the temperature of your location.
Buy a thermometer and hang it near your plants. For tropicals, the ideal night minimum temperature should be no lower than 58 degrees Fahrenheit (14.4 degrees Celsius) and the daytime maximum temperature no higher than 75 degrees Fahrenheit (23.9 degrees Celsius).
Choose a location with good natural light.
Small plants can be placed in the windowsill — just make sure the leaves don’t touch the glass. If your windows leak cold air, caulk them or move the plant away from the glass to avoid cold drafts.
Check your plants at least every other day to see if they need water.
As the surface of the soil dries, it will become lighter in color. Use your index finger to check the soil for moisture. Water when the top three-quarters of an inch of the soil feels dry.
Reduce the amount of fertilizer you give your plants.
That’s because with the decrease in day length and the house being cooler in winter than summer, plant growth slows down. Some plants, such as succulents, may even go into a state of dormancy or partial dormancy. With slower growth, plants need fewer nutrients than during periods of continued growth. As a result, you can cut fertilizing in half from the recommendations on the container's label. "We cut the dosage and frequency in half in our greenhouses in winter, from 200 to 100 ppm and from twice a month to once a month," Brinkman said.
Ideally, the humidity in your home — the amount of moisture in the air — should be between 30 and 50 percent, according to the Environmental Protection Agency (EPA). Humidity that's too low or too high can cause health problems for you and issues for your furniture and the home itself. One way to test home humidity is with a hygrometer, a device that looks like a thermometer and can be purchased at a hardware store. If the humidity in your home is less than 50 percent, Brinkman suggests choosing plants that have thick waxy leaves and avoiding thin-leaved plants. "Many digital home thermostats installed in the last five years have a humidity sensor and the percent of relative humidity appears on the screen along with the temperature," said Brinkman. Relative humidity is the ratio of the actual amount of water vapor present in a volume of air at a given temperature to the maximum amount that the air could hold at that temperature, expressed as a percentage, according to How Stuff Works.
"Humidity sensors are far more accurate than they were 10 years ago, so you may not need a hygrometer," Brinkman continued. "The maximum relative humidity houseplants can tolerate is 80 percent, but most people would find that intolerable in their homes. If you've created an enclosed microclimate for your plants, like a terrarium, remember to ventilate it occasionally to control humidity and allow CO2 inside."
Take steps to raise humidity if needed.
These steps can include:
- Putting plants on a saucer with pebbles and water. Just be sure the level of the water is below the top of the pebbles. If the bottom of the pot touches the water it can wick the water up into the pot, which can cause root rot. This technique will raise the humidity around the plant but not in a larger area, such as the room where the plant is growing.
- Mist your plants, but be aware that this comes with a caveat. "I'm often asked about misting with a hand spritzer," said Brinkman. "Misting doesn't hurt, but it’s not really effective either. The effect is too localized and too temporary. Instead consider a humidifier to raise the humidity."
- Consider choosing a humidifier with a built-in hygrometer that maintains humidity within a healthy range.
- Grouping plants. Plants growing in a "community" will naturally raise the humidity around them.
Dust your plants.
Left alone, dust can collect on leaves and reduce the amount of moisture the leaves absorb. Simply dip a soft cloth in water and wipe down the leaves.
Check for spider mites.
You can do this while dusting your plants. These pests thrive and reproduce rapidly in warm, dry air, which is why winter is the season you're more likely to find them. Look for tiny dust-like particles on the tops and bottoms of leaves. If you detect an infestation, take the plants to a sink and spray them with a stream of water to knock the mites from the leaves. If the infestation persists, spray the plants with insecticidal soap or horticultural oil, being sure to thoroughly cover the top and undersides of the leaves. Proper watering will help reduce pest infestations.
Run a small fan near your plants.
The air circulation is good for them. Think of it this way: Don’t you enjoy a gentle breeze on a warm day?
The don't list
Overwintering large tropical plants in an unheated dark garage.
"True tropicals, the ones from lowland moist tropics, need year-round warm and moist growing conditions," said Brinkman. "In nature, they never experience an extended cool dry rest or light deprivation. Three months in an unheated dark garage could likely produce an irreversible setback. Bring them indoors! Even a dry indoor climate is definitely better than an unheated dark garage."
Letting plants sit in saucers with water.
This will cause root rot.
Re-potting in winter.
Wait until spring, unless the plant is so pot-bound it's becoming obviously stressed. If you must re-pot, avoid over-potting (using a bigger pot than necessary). Choose a pot that is slightly bigger than the root ball rather than using a pot you think is in proportion to the leaf mass.
When spring does return (and it will!), here’s a final tip for any houseplants you might move outside in the spring and not bring back indoors until temperatures drop again in the fall. Move them gradually in steps into their ideal light conditions. Moving plants from the low-light conditions of most homes directly into the brightest light they can tolerate may result in sunburn — black spots — on the leaves. That sunburn will not go away. Instead it will serve as a lasting reminder not to make this mistake again.