How to Fight Stem and Root Rot

by Matt Gibson

So you may have overwatered your plants once or twice. Then you start to see the leaves getting dull, turning yellow, and looking rather sick. You take steps to correct the watering issue, but the plants don’t bounce back. Chances are, your garden is suffering from root and stem rot. These types of garden rot is caused by one of two issues. Either your plants got waterlogged due to overwatering or improper drainage or a fungus in the soil attacked and infected the roots.

If the crown or major roots are affected, your plants are in for some dark times, and without immediate help, they will wither away and die. There are some actions you can take to save them, but if the roots are too far gone, it’s best to discard, disinfect, take preventive measures against future attacks of fungal disease, and start again.

Not sure whether root and stem rot is the culprit? Smell the base of your plant around the root area. If it smells awful and moldy, it’s probably root rot. Remove the plant from the soil. Do the roots look white, firm, and healthy? Or are they brown and slimy? If they are brown and slimy, root rot is most likely the cause.

Symptoms of Root and Stem Rot

If you notice that your plants are slowly wilting and the leaves are turning yellow or dull for no known reason, these are all signs of root rot or stem rot. The wilting and dulling of color may happen quickly, or over the course of several months.

Check the roots of one of the plants by removing it from the soil and feeling the roots with your hands. If the roots feel mushy and look dark instead of a creamy white or tan, these are symptoms of root rot issues. Sometimes, infected roots will fall off when you touch them. Some healthy roots can be black or dark-colored, but they will still be firm to the touch, not mushy or limp. However, most healthy roots will be light-colored, which means that they are functioning well and are not suffocated by wet soils with insufficient soil drainage.

Healthy roots have smaller feeder roots, or rootlets, which can be easily spotted when checking the root system. On plants affected by root rot, the feeder roots will no longer be attached. Usually, if the roots are affected by rot, crown rot will manifest as the crown of the plant will also begin to turn brown or darken in color.

Treating Root and Stem Rot

In order to treat plants affected by root rot, early detection and swift action must be taken for disease management in order to save your crops. If you caught the problem early enough, there’s a good chance that you can address the issue and give your plants a fighting chance to bounce back. Remove the affected plants from the soil, and gently wash the roots under running, clean water. Wash away as much soil as possible, and don’t worry about any affected roots that fall off in the process. Try and be as gentle with the plant as possible while you’re treating them, though.

Using a sharp, clean pair of gardening shears or scissors, cut away all of the remaining roots that are affected. This may involve removing the majority of the root system if the plant is severely impacted by rot. If so, re-clean the scissors with rubbing alcohol after removing infected roots, and then trim back one-third to one-half of the plant growth. Because the plant will not need to support as much top growth once it’s trimmed, it will have a better opportunity to regrow the root system and grow healthy plants.

Using a sharp, clean pair of gardening shears or scissors, cut away all of the remaining roots that are affected. This may involve removing the majority of the root system if the plant is severely impacted by rot. If so, re-clean the scissors with rubbing alcohol after removing infected roots, and then trim back one-third to one-half of the plant growth. Because the plant will not need to support as much top growth once it’s trimmed, it will have a better opportunity to regrow the root system and grow healthy plants.

Resume treatment by disposing of all the soil in the pot that the plant was in. If the plant was not in a pot, you may consider potting it now and treating the garden bed soil with a fungicide and/or solarization to get rid of any soilborne fungus. After throwing out the soil from the pot, wash the pot thoroughly with a solution that is one part bleach and nine parts water. If you have fungicide on hand, dip the remaining roots in the fungicide to kill off any fungal diseases that may be lingering. Now that the root rot has been treated and the pot has been sanitized, repot the plant in fresh, clean potting mix.

Make sure that the plant’s new container has good drainage, and only water it when the soil surface is dry as a bone. Allow the plant five to seven days to regrow its root system before adding any fertilizer, as it may shock or stress the recovering plant.

Control

There’s no getting around it: all badly affected plants need to be removed and destroyed. Only try to treat moderately affected plants. If you are dealing with container plants the control process is simple to fix. Toss out all impacted soil, as you don’t want to risk recontamination. Thoroughly clean all containers with a bleach solution that is one part bleach and nine parts water. Don’t forget to clean any and all tools that you used during the process of decontamination, including your gloves and even shoes.

If you were gardening in the ground or in garden beds, control may be a bit more difficult and time-consuming process than you had hoped, but it’s not impossible. One method you may want to consider is a fungicide soil drench. This can be a costly process, and you will want to get help from a professional if this is something you want to look into. The recommended approach to prevent future problems is soil solarization.

Soil solarization is the process of covering your soil with a tarp so that it heats and soil temperatures reach 125 degrees Fahrenheit, killing off any fungal spores and bacteria that the soil may be harboring. Not only does soil solarization kill fungus and bacteria, it also wipes out a wide range of other pests that can wreak havoc on your garden beds, including nematodes and noxious weed seed. Plus, heating up your soil using solarization also stimulates the release of nutrients from the organic matter that is present in the soil. So after the solarization process is complete, your garden beds will be ready to produce like never before.

First, till the top layer of the soil. Then, rake the top layer until the surface area is smooth and even. Because wet soil conducts heat more efficiently than dry soil, water the area you plan to solarize until it is damp—but not so overwatered that it becomes soggy, as too much water will keep the temperature from reaching the level needed to kill off the fungus. Once you have a garden full of tilled, level, damp soil, you’re ready to cover it with tarp.

If you live in a warm climate area, cover your garden beds in clear plastic tarp for four to six weeks during the summertime. Ideally, the top six inches of soil will reach temperatures of up to 125 degrees Fahrenheit. If you live in a cooler climate area, use a black tarp instead of a clear tarp, as black tarp will attract the sun’s rays and increase the temperature underneath. In cooler climates, you will also want to leave the tarp in place for eight to 10 weeks, giving it more time to kill off all the fungus, bacteria and pests in the soil.

Preventing Root and Stem Rot

The only true way to fight root and stem rot is prevention. The two main components that lead to rot are temperature and oxygen. Plants, like all living things, need to be able to breathe in order to function properly. If the roots can’t breathe, the plant can’t grow. Prevent this lack of oxygen by making sure that roots are planted deep beneath the soil and that the soil is packed in loosely enough to allow oxygenation. If you are using a hydroponic or aeroponic growing system, make sure your air pump and air stones are large enough to keep water bubbling to allow plentiful amounts of oxygen to reach the root systems.

Hot temperatures are another thing that can lead to mold and mildew infestation and poor soil conditions. Unfortunately for outdoor gardeners, there’s not a lot that you can do to change the weather, so if you live where you have warm weather, consider adding rocks underneath the soil to improve drainage, and add mulch on the top layer to cool off the soil underneath. Use cool water when hydrating your plants as well, as hot water and hot weather is a bad combo for mold and mildew. Indoor gardeners may simply want to turn up the air conditioning during the summer months and provide plants an environment with proper ventilation.

Root and stem rot is not an uncommon problem, nor is it the end of the world. However, now that the problem has been identified, it’s time to work on a solution. Treating, controlling, and preventing root rot can be an arduous process, but anything worthwhile takes a bit of blood, sweat, and tears. If root and stem rot have taken hold of your garden, don’t give up hope—take up arms. You are now equipped with all the weapons you need to win the fight against rot and take your garden back.

Want to Learn More about Stem and Root Rot?

Gardening Know How Covers Treating Root Rot in Houseplants

GrowAce covers Root Rot: Prevention, Detection, Elimination

SFGate Homeguides covers How to Fight Root Rot

Texas A&M Extension’s Plant Disease Hand Book covers Stem and Root Rot

Veggie Gardener covers Root Rot

Weekend Gardener covers Root Rot

Weekend Gardener covers Will Soil Solarization Kill Fungus