By Mary Small, Colorado State University Cooperative Extension, Urban Integrated Pest Management
The number one killer of house plants is over-watering, and plants are especially vulnerable to this during the winter months largely because of reduced light intensity. House plants tell you they are getting too much water when their lower leaves turn yellow and drop off. Sometimes brown or black spots appear on the leaves. The roots often become mushy and turn black or brown, but you would have to knock the plant out of the pot to see this symptom. The plant also might wilt.
One of the best ways to accurately determine a plant's need for water is to poke your finger in the soil to the root depth. (How deep this is will depend on the size of the container. For example, for a 4-inch pot, poke your finger in the soil to at least your first or second knuckle; deeper for larger pots.) Notice how the soil feels. If it feels dry, it is probably time to water. If it still feels moist, check again in a day or two.
When you water, pour enough on so the soil becomes saturated and the excess drains out of the drainage holes into the sink or saucer underneath. Let the pot drain for 15 minutes or so, then discard any excess remaining in the pot's reservoir or saucer.
Don't use the surface of the soil as an indicator of a plant's water needs. During the winter, the upper surface of the soil dries out quickly as a result of the furnace running.
Photograph courtesy of Judy Sedbrook.
© CSU/Denver County Extension Master Gardener 2010
888 E. Iliff Avenue, Denver, CO 80210
Date last revised: 01/05/2010