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Humidity Hacks + How to Overwinter Tropical Plants Indoors

Written by Gloria Ballard

November 26, 2022

Cool days, low humidity, and frosty nights mean the end for any tropical plants outdoors. By now, the tropical hibiscus, rubber plant, Boston fern, mandevilla, parlor palm and any other cold-fearing specimens you want to save should be inside, snug and warm, where you can care for them as you would for any other houseplant.

But heated indoor air presents other problems. Typically, the air inside a home is drier in the winter, and tropical plants – including houseplants – may suffer from too little humidity, the amount of water vapor in the air. We’ve rounded up a few humidity hacks, easy ways to raise the moisture level in the air around your indoor plants. And read on for more tips to overwintering outdoor tropical plants indoors.

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Assemble a pebble tray

Placing humidity-loving plants in a pebble tray is an efficient way to raise the moisture level around them, and requires minimal maintenance once it’s in place. You’ll need a shallow, waterproof tray large enough to accommodate the plants, clean pebbles, small stones or gravel, and water. Assembling several plants in one tray increases the efficiency.

Fill the tray about halfway to the top with rocks and add enough water to cover them about halfway. Set the plants in their pots on top of the stones; the pots should not be in the water, but just above it. If you have several plants in one tray, you can also place small jars or bowls of water among them to increase the moisture.

To keep the tray from becoming a breeding ground for fungus gnats or other pests, rinse the tray and the rocks every few weeks.

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5 More Ways to Raise the Humidity Level 

  • Group plants close together. Plants placed together form local pockets of humidity as they transpire, and they can benefit one another this way. Placing a few glasses of water among them gives another small boost. 
  • Use a humidifier. A cool-mist humidifier can raise the moisture level in the air significantly. Here’s a tip: if you want to know the actual level of relative humidity in the air in your rooms, invest in a hygrometer, an instrument for measuring the air’s humidity. Houseplant experts note that most houseplants thrive in an environment where the humidity level is around 60 percent,  
  • Spray plants with a fine mist. A frequent spritz goes a long way toward keeping some plants happy, but other plants, such as hairy-leaved African violets, should not be misted. Excess water on the leaves will be harmful over time. 
  • Use a terrarium. If you have a number of small plants, group them together inside a glass terrarium, where they create their own tropical environment. A smaller, single plant that needs high humidity can be covered with a glass cloche.  
  • Of course, you can also choose to keep plants in the most humid room in the house — often a bathroom, where the shower adds a daily dose of moisture to the air. If the room doesn’t get enough natural light, you may need to add supplemental lighting.

How to care for outdoor plants indoors

After you’ve inspected your plants for pests and brought them inside, don’t forget about them. Tropical outdoor specimens still need care and attention once they’re indoors. 

Their most crucial need may be light. Plants that grow outdoors in summer may suffer from the lower light inside the house, so place them near the brightest windows in your home, or provide supplemental lighting with artificial lights. 

In general, the plants won’t need as much water as they did in the summer. In fact, too much water can cause root damage. They do, however, need more humidity than they can get from heated, dry indoor air (see above). Monitor the soil, and water when the top inch or so of soil in the pot is dry.

Watch for pests. Even if you know the plants were clean when you brought them in, they can still be attractive hosts for some of the most common houseplant pests. Watch for mealybugs, aphids, whitefly, scale and spider mites. Signs of these pests may include webbing, a sticky substance on the leaves, tiny yellow spots or cottony white spots on stems or leaves. 

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