Just like people or pets, houseplants are subject to a variety of diseases. Sometimes they can be bad enough to kill a plant. But if you know what to look for, you can usually spot early warning signs of diseases and take action to control them.
Many common houseplant diseases are opportunistic, infecting plants that are stressed due to unfavorable growing conditions. So the first thing do to prevent disease outbreaks is to provide the best growing environment possible. This means using quality potting soil, giving plants the room they need to grow, avoiding drafts or dry air from heating vents, and providing adequate temperature, humidity, light, water and drainage.
What To Watch For
Your plants will let you know if they have a disease problem; growth slows, stunts or becomes spindly; leaves turn yellow, show white powdery blotches or develop spots. Infected leaves eventually drop. Plant stems may become soft and mushy, with black discoloration near the soil. Some of these symptoms are easily confused with signs of insect problems, so make sure you can also recognize common houseplant insect pests.
Wet, waterlogged potting soil – either from overwatering, poor drainage (usually from letting water sit in drainage dishes) or soil compaction – causes roots to suffocate and die, changing their white tubular appearance for a spongy, blackened mess often called root rot. Root problems usually cause a plant to wilt, even though soil is moist. To check for root issues, remove the plant from its pot. Look for blackened, mushy roots. You might also detect sour or ammonia odor
Five Common Diseases Of Houseplants
Learn to recognize these symptoms of common diseases.
Gray Mold: Also called Botrytis; it’s a fungal disease that can infect every part of a plant, including leaves, stems and flowers. To control, regularly remove dead leaves and flowers from stems and laying on the top of the soil, and provide adequate air circulation. Commonly infects Begonia, African Violet and Cyclamen and other flowering houseplants.
Powdery Mildew: White powder appears on leaves, especially new growth, which can become deformed. Often doesn't kill plants, but can cause leaf drop and weakening. Improving air circulation will help reduce problems.
Leaf Spot: Yellow, brown, black or water-soaked, round or irregular shaped spots on the foliage. When severe, spots coalesce and kill the leaf. You might also see brown dusting on leaves and blooms. Common on Dracaena and Dieffenbachia. Thrives in high temperature and humidity, and poor air circulation.
Root Rot: The first signs are wilting and yellow leaves. When it really gets bad, the entire plant collapses. Caused by poor drainage and overwatering. Once a plant is infected, root rot is hard to cure. To prevent, allow plants to partially dry between waterings and don’t let pots sit in drainage pans filled with water.
Viruses: Cause distorted, streaked or mottled leaves, or reduced plant growth and flowering. Viruses are often incurable – and many are contagious to other plants. If you suspect a virus, isolate the infested plant and provide perfect care to rule out other diseases. Better yet, throw it away.
Dealing With Diseased Houseplants
Follow these steps to help prevent disease or spreading them from plant to plant:
- Isolate diseased plants so the disease can’t spread.
- Wash hands between caring for different houseplants.
- Sterilize tools when moving between different plants. Use a solution of 1 part bleach to 10 parts water.
- Water properly – don't overwater or underwater. Allow plants to partially dry between waterings and don’t let pots sit in drainage pans filled with water.
- Make sure plant is getting the right amount of light; adjust a plant's location accordingly and with the seasons.
- Improve air circulation. Ensure that air flows freely around plants and that they are not overcrowded. A small fan can improve airflow.
- Give up on problem plants. Sometimes it’s best to just throw them away.
For more information, see How To Grow Healthy Houseplants.