ITG overwintering houseplants

Placement of houseplants is key during winter.

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Winter is a stressful time for many plants in the landscape, given the drought conditions brought on by freezing temperatures and the effects of extreme cold.

Although these stressors typically don’t impact our houseplants the same way, indoor plants experience their own form of winter stress, making wintertime one of the most common times of year for decline or death of houseplants.

Similar to outdoor plants, wintertime brings some challenges with water to our houseplants, although we can do a lot to reduce the impact by paying special attention. Surprisingly, more houseplants die during winter from overwatering rather than under watering. It’s just not a time of high water demands since growth rates are reduced by dwindling sunlight and often lower indoor temperatures. When plants aren’t growing as much, water demands are much lower. Overwatering can lead to poor growth and serious root issues since persistent moisture allows root rotting fungi to become established.

Most houseplants do best when soil is allowed to nearly dry out completely between watering. Since growth and water uptake are less in winter, it is really important to modify watering times accordingly. The best way to monitor soil moisture is by feel. Use your finger to feel the upper 1-2 inches of soil a few times a week in order to get dialed in. Only add water when you feel the soil has dried out and water thoroughly to ensure the entire pot is saturated.

If they are small enough, lift the pot up and test the weight each time you check soil moisture. For most of my houseplants, I can tell when they need water from their weight since the soil medium dries out so much. Pots often weigh half as much as they do when saturated.

Boosting humidity

To compound the watering issue, indoor air is often very dry during winter with relative humidity sometimes plummeting below 20 percent. Since most houseplants prefer 40-50 percent for normal healthy growth, low humidity brings on additional stress.

If you have a humidifier, move houseplants a little closer this time of year to boost humidity. Another very simple solution is to cluster your plants by placing them close together for winter. As they naturally release water by transpiring, the group will benefit from the microclimate they create. Kitchens and bathrooms often have higher humidity, making them great overwintering locations if they receive adequate light and you have the window space.

If moving plants isn’t an option, add a shallow tray of water below your plant to add humidity. Be sure to keep the pot up out of the water so the soil medium isn’t able to wick up moisture. Many folks place decorative rocks in a tray to boost pots up out of standing water.

The age-old practice of misting leaves is actually of negligible benefit given the relatively short humidity boost it provides unless you are misting constantly throughout the day. I didn’t realize this until I purchased a small, digital thermometer and humidity gauge. The effects from misting only lasted minutes compared to the constant slow release from a shallow tray.

Light is perhaps the greatest factor limiting houseplant growth in winter. As days grow shorter and the sun dips lower on the winter horizon, the light reaching houseplants can vary dramatically. Pay attention to the sun’s angle to be sure your sunny, south facing window still receives adequate light during winter. Some north and east facing windows that were great indirect light during summer can become too shaded during winter. As shade trees lose their summer canopy, windows with filtered light during summer can become nearly full sun in winter. Be sure the light reaching houseplants isn’t changing more than you realize during winter.

Placement is critical

Dramatic swings in environmental conditions are incredibly difficult for plants and the indoor winter environment can often create huge daily fluctuations in temperature. Take care to be sure houseplants are away from drafts, cold windows or heat vents. Most houseplants prefer a daytime temperature between 65 degrees and 75 degrees with only about a 10-degree drop at night. A digital thermometer placed near your plant can help track temperatures to ensure the daily fluctuations aren’t too extreme.

Research has identified a whole suite of health benefits provided by indoor plant life. So, houseplant care is important for both plant and human health. I often think of the indoor environment as more controlled than outdoors, making plant care easier. However, the changes to our indoor environment in winter are often very subtle and slow, requiring careful attention to avoid added stress on houseplants. This year, take note of light and moisture levels to better control the indoor winter environment for the benefit of all your indoor plant life.

Ryan Pankau is a horticulture educator with the UI Extension, serving Champaign, Ford, Iroquois and Vermilion counties. If you are interested in reading this weekly column online, visit his "Garden Scoop" blog at go.illinios.edu/GardenScoopBlog.