Humidity and Houseplants

Potted plant on a windowsill with a glass of water nearby.

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The typical home has low humidity, yet many houseplants prefer a more humid environment. Some favorite houseplants come from tropical or subtropical regions where they flourish in the loamy, humid underbrush of a larger forest. These origins mean that these types of plants are poorly acclimated to growing in a typical home. Many of the aroids and most popular orchids fall into this category, and even English ivy is meant to grow in humid and misty forests.

The Percentage Disconnect

For these plants, a humidity of even 50 percent isn't enough, and some prefer humidity to reach up into the 80 percent range. By contrast, many homes are virtually bone dry, especially in the winter months as heat pumps kick on and blow hot, dry air throughout the home. In these homes, a humidity of 20 percent is generally normal.

If the idea is to grow your plants in as close to their natural environment as you can get, there is a substantial disconnect here. As a result, indoor gardeners are forever looking for ways to increase humidity.

How to Increase Humidity

Before undertaking any of these, make sure your plant is of a type that requires higher humidity. If you know where it's from originally, that's a good clue. Alternatively, look for signs of humidity stress, such as brown leaf tips or brown leaf margins.

Once you've determined that higher humidity is warranted, any of the following ideas can be used to increase humidity:

  • Group your plants. Plants release moisture through their leaves in a process called transpiration. By grouping plants together, you create a more humid microclimate in your growing area that will benefit all the plants. It's also a good idea to keep plants with similar humidity requirements near each other. For example, if aroids are your passion, group all your aroids in one place where their more rapid transpiration rates will create higher ambient humidity in the growing area. This, however, would not be an ideal place for a succulent or cactus, both of which require lower humidity levels.
  • Put the plants in trays with pebbles. This is a popular way to raise humidity immediately around your plants. Use clean trays and put at least an inch of pebbles in each tray, then set the pots on the pebbles. Fill the tray with water halfway up the pebbles, but don't let the pots sit directly in water, which will encourage root rot and plant collapse. Every time you flush your plants, make sure to empty and rinse the tray. This will ensure that the tray doesn't become a breeding ground for insects and it will reduce the concentration of fertilizer salts that have accumulated in the tray.
  • Mist your plants. This is another popular method to increase humidity. Keep a misting bottle filled with clean water near your growing area and spray the plants every so often. Misting is especially helpful at the beginning of the winter season when the humidity drops rapidly with the temperature. However, some plants should never be misted, including any plants with hairy or velvety leaves, such as African violets. Misting these plants encourages diseases that can be fatal.
  • Use a humidifier. Humidifiers will raise the humidity in the whole room, but they are an excellent way to increase humidity in a growing environment.
  • Use a terrarium. If you're growing plants that cannot be satisfied no matter what you try, consider switching to terrariums. A terrarium is an enclosed environment with some soil and a few small plants. The system is sealed, so the plants take up moisture, "exhale" it through transpiration, only to then have the moisture gather on the walls of the terrarium and fall back into the growing media much like the water cycle in the outdoors. Terrariums are perfect for smaller plants that require higher humidity and temperatures.