Growing houseplants is a challenging and rewarding hobby that can be enjoyed by everyone and need not be difficult. Give plants what they need and they’ll do well. Learn from ISU Extension horticulturists just what it is that houseplants need. To have additional plant and garden questions answered, contact the ISU Hortline at 515-294-3108 or firstname.lastname@example.org.
Dust and grease often accumulate on the leaves of houseplants. The dust and grease not only make them unattractive, it may slow plant growth. Cleaning houseplants improves their appearance, stimulates growth and may help control insects and mites.
Large, firm-leafed plants may be cleaned with a soft sponge or cloth. Wash the foliage using a very dilute solution of dishwashing soap and tepid water. Another method is to place the plants in the shower and give them a good bath. Be sure to adjust the water temperature before placing the plants under the shower head.
The black, sooty material is likely sooty mold. Sooty mold is caused by several different fungi. The fungi don’t infect plants, but grow on the sugary substance (honeydew) excreted by scales, mealybugs, whiteflies and other sap-sucking insects.
Sooty mold causes little harm to houseplants. The damage is mainly aesthetic. The black, soot-covered leaves aren’t very attractive. However, the sap-sucking insects may seriously harm houseplants. Scales, mealybugs and whiteflies are very difficult to control. Discard the pest-infested plant or follow recommended control measures. Control efforts will require patience and persistence.
The white material on the foliage of your African violet is probably powdery mildew. Powdery mildew is a fungal disease that is common on indoor plants, such as African violets, begonias and poinsettias. Outbreaks of powdery mildew on houseplants typically occur in winter or early spring. High relative humidity and poor air circulation favor powdery mildew development on houseplants.
If only a few leaves have powdery mildew, pinch them off and discard them to keep the fungus from spreading. Humidity levels can be lowered by increasing the spacing between plants. Moving plants out of rooms with high humidity (kitchens and bathrooms) is another option. While fungicides are available for use against powdery mildew, cultural controls are the preferable way to control powdery mildew on plants in the home. Severely infected plants may need to be discarded.