Root rot of house plants

Photo by Jill and Laurie Thomson. A Dieffenbachia (Dumbcane) plant shows signs of rot in the lower part of root system because water did not drain from bottom of pot.

When you live in a climate that is winter for half the year it is not surprising that many of us like to have indoor plants that provide us with growing vegetation in our homes. Some of us even put these plants outside for the summer months, and bring them back inside as the climate becomes incompatible. One of the most important factors for keeping your plants healthy and happy indoors is to learn about their likes and dislikes for temperature, light, soil type and watering. It is also important to bring them into your house in as healthy a condition as possible.
Watering and soil conditions are both critical in keeping the root system of your house plant healthy. Most plants do not want to sit in waterlogged soil; some (like ferns) will tolerate wetter soils for longer periods, and enjoy high humidity. Others (such as cacti) prefer soils that drain quickly and dry out between watering. So it is important to find out the requirements of your different plants, and not to treat all in the same way; maybe separate them physically, which makes it easier to keep the conditions required by different types of plants in separate locations.
When the roots of a plant remain in damp soil they are more prone to attack by fungi and bacteria that can cause rot. These pathogens may be introduced in your soil or be imported on the plant roots. Rot usually occurs when conditions are better suited for the pathogens rather than the plant roots. A wise precaution, when acquiring a new plant, is to repot it in a container that has adequate drainage, using potting soil of the correct nature for the type of plant. As an extra precaution, you can sterilize your soil by baking in the oven in a covered container for at least 30 minutes at 180-200 °F prior to planting.
The symptoms of root rot include yellowing or blackening of leaves that eventually die and drop off, despite adequate watering. The presence of fungus gnats indicates the soil is staying too moist for long periods, and root rot may develop. Also if the soil and plant become smelly, root rot may be present.
If you suspect rot, carefully remove the plant in its clump of soil, place in a shallow bowl of water, and tease the roots apart. If the roots are dark, blackened, soft and squishy then they are likely rotted. Healthy roots are usually creamy white to tan in colour and are firm to the touch. Often only part of the root system is affected and it is possible to cut the damaged roots back to healthy tissue, using scissors or pruners dipped in disinfectant (1 part bleach to 3 parts water). Cut back the above ground foliage, to match the amount of root remaining, then repot the plant in a container that has been washed and rinsed in bleach solution. Use sterilized potting soil, and place in growing conditions suitable for the plant. Always water pots separately so they are not sharing water draining from other pots, as this prevents pathogens from moving between pots and plants.
Drainage is extremely important and many attractive pots have no drainage holes. Find a smaller plastic pot with drain holes that will fit inside the decorative pot, and either sit the inner pot on a bed of gravel or, better still, remove it when watering, replacing once any excess water has drained away.
Plants do not easily recover from root rot. It is worth spending time on finding out what conditions suit your plants, in particular the water regime, to avoid root rot altogether. However, even if the root system is damaged, it may be possible to root a cutting from a stem. For example, coleus, ivy and other plants will form healthy roots on stems that are placed in water for a few weeks – it is worth a try!
Jill Thomson is a retired Plant Pathologist who lives in Saskatoon, where she enjoys gardening with her children, grandchildren and the dogs. This column is provided courtesy of the Saskatchewan Perennial Society (SPS; ). Check our website ( or Facebook page ( for a list of upcoming gardening events.