Root rot, also occasionally called “soil fungus”, is a serious plant disease that can impact indoor and outdoor plants alike. As the name “root rot” already suggests, these infestations cause the roots of affected plants to rot, typically with fatal consequences for the plant or tree. The most common causative organisms are fungi (molds), with the the Phytophthora genus representing a common culprit. Of all the molds that can cause root rot in plants, the species Phytophthora cinnamomi is the most destructive, killing plants with shocking speed.
Because root rot is so often a death sentence for plants, keen gardeners will want to take proactive steps to prevent the onset of these infestations — rather than attempting to cure the plant after root rot has already taken hold.
Thankfully, that is a lot simpler than many people think. Excessive moisture and a lack of drainage lie at the root of Phytophthora cinnamomi infestations, and the same holds true for other organisms that lead to root rot. Root rot is, in this regard, no different to any other mold infestation.
With the right care, the vast majority of root rot cases can effectively be prevented. Should a plant already have developed root rot, it can sometimes be treated successfully.
What does Root Rot look like?
The initial symptoms of root rot are only apparent with the root system of a plant or tree. They include browning of the roots’ tips, their softening, root lesions, and decay. Gardeners will only be able to observe this if they unpot the plant.
About Root Rot
- “Root rot” is an umbrella term that describes any pathogen that causes the roots of a plant to rot. These include fungi (molds), viruses, oomycetes, which are fungus-like, filamentous, and microorganisms. Indeed, parasites such as nematodes (microscopic worms) can also play an integral role in the proliferation of root rot, as the damage they cause offers entry points to root-rot-causing pathogens. Fungi are, however, the most common cause of root rot.
- Dozens of different fungi can cause root rot. Some can affect practically any plant, while others are species-specific. Some of the fungi that cause root rot are not commonly seen outside of that particular setting, while others, like Aspergillus spp., also cause household mold infestations.
- So-called black root rot is among the most common forms of root rot in ornamental plants as well as strategic crops. Black root rot is caused by two species of a soilborne fungus previously known as Thielaviopsisbasicola. Today, they are known as basicola and B. rouxiae. Examples of important crops affected by this type of root rot include cotton, carrot, and soybean.
- The fact that root rot infections start within the roots of a plant or tree, where symptoms go unnoticed due to the root systems being located underground, makes it especially hard to identify root rot in its early stages. By the time the plant starts displaying symptoms, such as stunted growth and wilting or discolored leaves, the plant or tree is already at risk of death.
- Poor drainage and overwatering and excessively moist or wet soil are the most common underlying causes of root rot. Ensuring that plants do not sit in excessively moist soil is the most important step any gardener can take in preventing root rot infections.
- In light of the fact that excessively moist soil is a primary cause of root rot, it will come as no surprise that — although any plant or tree can be affected by root rot — root rot is more common in ornamental plants grown in pots indoors, or within greenhouses.
- Root rot is unlikely to have any adverse effect on human health. However, extremely sensitive people, such as those with asthma, may notice respiratory symptoms after handling soil in which fungal species that cause root rot are proliferating.
- Fungal spores are present all over the natural world. For root rot to take hold, fungal spores do not merely have to be in close proximity to the plant. Fungal spores also need ample moisture, poor drainage (which forces the water to remain in close proximity to the plant’s roots), the right temperature (which varies from one species to the next), and favors plants that are already weakened by other factors.
Root Rot Features: An Overview
- All sorts of organisms can cause root rot in plants and trees. Fungi are the most common culprits, and common species include Fusarium, Phytophthora, Pythium, and Rhizoctonia You would need to conduct testing to identify the specific causative species. However, symptoms, prevention, and treatment for root rot are almost identical across causative agents. Therefore, if you are a home gardener, you do not need to take steps to find out about the type of fungus that caused the root rot.
- Once root rot advances, the tell-tale signs that point to root rot can also be seen in other parts of the plant. The most common symptoms include a plant that stops thriving, obviously declining in health and failing to grow, smaller, paler, leaves, and wilted, yellowing, or brown leaves. In some plants, the root rot will leave the root system and become apparent on the stems.
- If you notice these signs on an ornamental plant, the best course of action would be to unpot the plant, or remove it from its soil, to observe the roots more closely.
- Root rot can be contagious — once one plant is infected, nearby plants may also develop root rot. Likewise, gardeners who use the same tools to transplant various plants may inadvertently cause root rot to spread.
- While root rot is not seasonal, as such, it is important to remember that water lingers longer in colder conditions, as evaporation takes place at a slower rate. If gardeners do not adjust the amount of water they offer their plants during the fall and winter, root rot is more likely to set in. Some plants likewise have dormant stages during which they should either be watered less or not at all. Failing to keep up with their needs can contribute to root rot.
How Root Rot Begins
Root rot — regardless of the fungus or other microorganism that causes it — greatly prefers excessively moist (wet or soggy would be excellent descriptors as well) stagnant conditions with poor drainage. Spores of the fungi that can cause root rot may be present at any time, especially in garden soil, but root rot cannot take hold unless the causative agent has access to sufficient humidity.
Because of this, the risk of root rot increases in slightly cooler fall or winter conditions — weather patterns that are well above freezing, but too cool for water to evaporate quickly, are ideal for fungi that cause root rot in plants and trees. However, given truly excessive watering, root rot can take hold in warmer conditions as well.
Root rot can affect trees and plants that are grown outdoors; many of the strategic crops that are under constant threat from root rot are, indeed, cultivated outside. However, because root rot favors consistently wet conditions, houseplants and other potted plants are especially vulnerable to root rot if the pots cannot drain.
Plants and trees located within soil that has become waterlogged are at risk, as well. Fungal spores — some of which can attack almost any plant, while others prey on specific species, such as conifers or succulents — are able to remain dormant within the soil for prolonged periods of time. Once enough water is introduced, and it remains in place, those spores can activate and start proliferating.
These fungal spores can spread to other plants through irrigation systems, or even through gardening tools.
What Causes Root Rot in Plants?
- Poor drainage. Most house plants are “housed” in pots that don’t have drainage holes — making them some particularly susceptible to root rot. Without any way for the water to escape, it starts to build up, making the pot a perfect place for root rot to begin thriving.
- Excessive watering. The number one contributor to root rot is watering your plant too much. If you give your plant more water than it needs, you’re practically asking for root rot. It is important to pay attention to seasonal changes, and always ensure that a plant receives sufficient, but not excessive, water.
- Excessively large pots. A lesser known cause of root rot is placing your plant in a a pot that’s too large for it. The extra space won’t end up being used but instead will be full of water. Keep your plants in appropriately-sized pots and only “upgrade to a larger model” when needed.
- Winter and fall weather. Root rot thrives in colder conditions, especially in winter and fall, due to decreased evaporation.
- Not draining the tray. If you forget to regularly drain the tray underneath your pot, your plant could get root rot.
- Sick plants. Root rot preys on plants that are already weakened and sick. Whether this be a physically damaged plant or one that is not fertilized enough, a weakened plant is at risk of root rot and needs to be monitored especially closely.
How to Prevent Root Rot in Plants
Root rot can often be prevented by ensuring that your plants are watered appropriately, and never overwatered. Indoor houseplants should be placed in pots with adequate drainage. Outdoor plants and trees risk becoming waterlogged in case of soil types with poor drainage, in which case you may wish to look into herringbone drainage for your garden.
In the case of trees, fungicides can also help to prevent root rot caused by fungal infections or mold.
How to Fix Root Rot in Plants
Treating root rot is challenging — and preventing root rot is always the superior option. If a beloved plant has developed root rot, however, there are steps you can take to try to remediate the problem and save the plant.
If you suspect beginning root rot because a plant is no longer thriving, has some wilted leaves, and you know that it was watered excessively because the soil is drenched, you may only need to allow the soil to dry before watering the plant again. As a responsible gardener, you should always look for information regarding the ideal watering frequency and the amount of water the plant needs. If the plant is kept in a pot without drainage holes, take steps to change that.
In cases of more established root rot, you can still try to save your plant. Here’s how:
- Remove the plant from the pot it was in as gently as possible. Carefully brush off the soil and then wash the roots to eliminate remaining contaminated soil.
- Prune any roots affected by root rot, along with withered leaves.
- The next step will be somewhat counterintuitive. You will have to prune the plant’s remaining healthy flowers and buds, or leaves, to match the extent of the roots you removed. This ensures that the now severely trimmed root system can sustain the remaining plant.
- The plant is now ready to be repotted. Ensure that you choose a well-draining soil type and a pot with ample drainage holes.
- Begin watering your plant again, but ensure that you do not overwater it.
Keep a close eye on your plant — and keep it away from its neighbors, just in case root rot is still present. If your plant shows signs of recovery, your efforts have been successful.
Root rot is the bane of gardeners and farmers everywhere, and it is most often caused by fungal species. By ensuring that your plants are watered appropriately and have proper drainage systems in place, you can prevent most cases of root rot. Plants already affected can sometimes recover with the right treatment protocol. The sooner you catch the signs of root rot, the better the chances that treatment will be successful. However, your efforts are best spent by taking steps to avoid root rot in the first place.