In many houses, especially in winter, the air is simply too dry for many houseplants. With the exception of cacti and other succulents, most houseplants thrive in an environment with a relative humidity of 50 to 60 percent. (Relative humidity is the amount of water vapor the air contains relative to the maximum amount it could contain at the same temperature.) A great way to determine the relative humidity near your plants is with humidity-indicator cards (available at garden centers) which will give accurate readings for about six months. Put them next to your plants, then adjust the humidity based on the readings. If the relative humidity is too low, the most effective way to raise it is to place a humidifier in the room. Misting the foliage frequently will also help raise humidity levels.
Learn how to make a Healthy Plant Tray to increase humidity for your houseplants.