Proper Humidity for Indoor Plants

Date: April 1989 (Revised April 1995)

Source: NDSU Extension Service Horticulturists

Humidity is one of the environmental factors you should consider in the care of indoor plants. If the humidity is too high, plants become susceptible to rot, mold and mildew. This is rarely a problem in homes, but if it is, you can control it with increased ventilation.

If the relative humidity is too low, plants lose water faster through the tiny openings in their leaves than they can replace it through their roots. Characteristic symptoms of this are browning leaf tips, yellow leaf margins, bud drop, shriveling and wilting. This is often a problem with indoor plants, especially during the winter with high indoor temperatures produced by artificial heat.

There are several ways to minimize the problem of low humidity in homes:

1. A good balance of soil mixture, proper temperature and correct light levels can help to overcome the negative effects of low humidity.
2. Install humidifiers in individual rooms or in heating systems.
3. Place a tray of water on a radiator to serve as a humidifier. Water, evaporated into the rising, heated air, spreads around the room as the air circulates.
4. Keep plants away from radiators and drafty locations; moving air picks up water vapor.
5. Place plants on a tray of wet pebbles. The water evaporates upward from the surface of the stones, creating a humid micro-climate around the plants.
6. Group plants together so that they can "break" the air currents blowing on them and also take advantage of the moisture evaporating from each other. Place a glass of water in their midst to increase the benefit.
7. Place plants in areas that are naturally higher in humidity; for example, near the kitchen sink, above an aquarium, in the bathroom.
8. Put especially sensitive plants in terrariums, where you can more easily control the environment.
9. Grow plants that have adapted to dry air; for example, cacti and succulents.