by Evin Morrison, Extension Master Gardener
Photos © Evin Morrison unless otherwise noted
As the chill of winter sets in, it’s not only humans who seek warmth and comfort; our houseplants need special care, too. During the colder months, low light levels and cooler temperatures can stress plants, slowing their growth, making them more susceptible to pests and diseases, and just not looking their best. Fortunately, with a little preparation and attention, you can ensure your indoor greenery thrives even in the harshest of winter climates.
Unfortunately, just moving our tropical plants indoors at summer’s end isn’t always enough to keep them from the harsh effects of winter.
Do a little research into your plant’s preferences
Bureau of Land Management, Public domain via WikiCommons
Each plant species has its own ideal temperature and humidity ranges. So, it’s important to research the specific needs of your houseplants. If you have the space, it helps to group plants with similar needs together to create a microclimate.
Tropical plants like ferns, pothos, and philodendrons prefer consistent, warmer temperatures in the high 60°F range with higher humidity. On the flip side, summer sun-loving succulents and cacti can tolerate cooler conditions, even dipping into the low 50°F range. Look at your plant’s natural environments: Rainforests have very little temperature fluctuation, while deserts are known to swing from extreme heat to extreme cold as soon as the sun dips.
Knowing the needs of your plants, you can create a more tailored environment that ensures they stay healthy, without accidentally overheating or freezing them.
Consistency is key
One of the most important factors in keeping houseplants warm is consistent indoor temperature. Extreme fluctuations in temperature can stress plants out and lead to stunted growth, leaf drop, or browning edges.
It’s important to check where your plants are situated. Drafts from windows and doors can cause sudden shifts in temperature, especially in older homes. Even in homes with modern, insulated windows, if you can notice a difference in the ambient temperature when you hold the back of your hand near the window, you can bet your plant will feel it, too. While opening a door and letting in a gust of cold air is one way to surely drop the temperature, the prolonged cold a plant might experience sitting close to a cold window might affect its health. While it seems warm and sunny all day, don’t forget the temperature can drop significantly at night. You’ll be snug in bed under a layer of blankets, but your plant will be freezing next to the cold glass. It’s also important to make sure that the leaves of your plants aren’t touching the glass, as they can easily burn from the cold.
As with everything with houseplants, we must find the happy medium. While we want to keep our plants warm and toasty, placing them too close to direct heat sources like radiators, space heaters, or fireplaces can dry them out. The hot, dry air can cause their leaves to curl, brown, or crisp up. Instead, place your plants a few feet from heat sources, where they can enjoy warmth without being subjected to harsh conditions.
Humidity is good for you and me
Indoor heating systems tend to dry out the air, which can be detrimental to many houseplants, particularly tropical species. Low humidity can lead to crispy leaf edges and browning. Species like calathea and stromanthe are particularly susceptible to browning from low humidity. Not only is it good for the plants but keeping a level of humidity in our homes is good for us, too!
Figure 7: This humidifier has a hose attachment that can be moved to direct the mist towards your plants.
Using a humidifier is the most obvious, but also one of the best, ways to keep humidity levels up. Set it up near your plants, or in the room where they’re located, and aim for a humidity level of 50%. Some humidifiers even come with built-in settings that allow you to control the level of moisture they release, which can be particularly helpful for humidity-sensitive plants. You can also use a thermometer and humidity gauge to keep an eye on specific areas you are trying to control. Many of these devices sync up to an app on your phone, so you can check without having to move from under your cozy blanket. Of course, with humidifiers make sure that the condensation isn’t building up on the leaves of the plants as that can lead to rot. And double check the furniture your plants are on as water droplets from some humidifiers can build up on the leaves then drip onto your surfaces. Keeping our plants alive through winter shouldn’t come with the added costs of water damage.
If you don’t have a humidifier, another option is a DIY humidity tray. Place a shallow tray filled with water and pebbles beneath your plants. As the water evaporates, it will raise the humidity level around the plant. Make sure the water level doesn’t reach the plant’s pot, as sitting in water can lead to root rot.
Many people recommend misting your plants, but it’s not the best option for increasing humidity. The effects are very temporary and can lead to over-watering problems if you over-mist and the soil gets saturated. However, the act of misting plants does feel proactive, so if you want to give it a go, mist early in the day so the water has time to evaporate before nighttime. Aim for the area around the leaves of the plant while avoiding the soil surface to help prevent mold or mildew growth. Keep in mind the effects are not long lasting and will not raise your overall ambient humidity.
Keep your pots warm
Even though your indoor temperatures may be relatively stable, the roots of your houseplants are still vulnerable to the cold, especially if you’re using pots made from materials that conduct heat or cold. Notice how cold your tile floors get compared to your wood floors and then compare that to carpeted areas. Most of us have our plants potted in ceramics very similar to tile, which hold the chill more than other materials. Insulating your pots can help keep your plants’ root systems warm and protect them from temperature extremes.
Lift your plants off the floor. Adding cork mats or trays that keep plants from being directly on the floor gives a buffer that can help keep the cold at bay. The goal is to help maintain a stable root temperature in the soil. Trays or stands can also add aesthetic appeal to your plant collection while being completely functional.
In very cold rooms, like a closed-in patio, try double potting. Place your plant’s pot inside a larger decorative pot, with a layer of insulating material—such as burlap or old beach towels—between them. This will protect the roots from sudden temperature drops.
If you are very concerned about a cold area in your home, you can also implement heat mats, but beware as this isn’t always the safest option for your plants. Heat mats are often used in seed starting to help seeds germinate, but once the seed has sprouted the mats are usually removed. We do this because too much heat can “cook” the roots. So, if you have a space that really needs a bump of warmth and there’s nowhere else your plants can go, you could give a heat mat (on a very low setting) a try. Make sure there is a barrier between the bottom of your pot and the mat, like cork rounds.. Also try to pick plants in containers that conduct the least amount of heat, like plastic. Ceramic can heat up much quicker than you might think and metal planters will get downright hot.
Keep an Eye on Pests
Cold weather doesn’t mean pests go away—they can still thrive in warm indoor environments. Be vigilant and regularly inspect your plants for common winter pests, like spider mites and mealybugs. Spider mites love low humidity environments and have a knack for floating from plant to plant on the air coming from heat vents. These little pests also tend to look like dust on the leaves. So, while we don’t notice them for a while, they are spreading throughout the house. Every time you water your plants this winter, give them an up-close and personal look. If you find anything suspicious, treat immediately and check all the plants nearby. Use natural remedies like neem oil or insecticidal soap to treat any infestations.
While we all wait for warmer days, keeping out houseplants warm and healthy during the winter months requires a bit more attention and care, but it’s well worth the effort. By understanding your plant’s needs, adjusting their environment, and keeping them protected from the cold, you can ensure that they not only survive the winter but thrive during it (and maybe even put on a little growth!)
These strategies will help create a warm, supportive environment for your indoor garden. By spring, your houseplants will be well-positioned to spring into action and reward you with vibrant, lush growth.