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Stoner Quelle • 04.03.2025

Root rot: causes, symptoms, prevention and effective countermeasures

Root rot is one of the most common and dangerous diseases that can affect plants. It occurs both in gardens and with houseplants or hydroponic systems and can lead to rapid plant death. Often, the infection goes unnoticed for a long time because the first symptoms develop in the roots and only become visible when the plant is already severely damaged.

This article provides a detailed and comprehensive look at root rot: from its causes and symptoms to the most effective prevention and treatment methods.

What is Root Rot?

Root rot is a disease of the root system caused by fungi or bacteria. It primarily develops in damp, poorly ventilated environments where harmful microorganisms can spread optimally. Affected roots turn brown or black, become soft and slimy. They lose their ability to absorb water and nutrients, leading to a rapid decline in the plant’s vitality.

Causes of Root Rot

The main causes of root rot include:

1. Waterlogging and Poor Drainage

Root rot often occurs when the soil or substrate remains too wet. Insufficient drainage prevents water from flowing away properly, keeping the roots damp for a prolonged period. This significantly reduces oxygen exchange in the root area. Without enough oxygen, roots die and become susceptible to fungal infections.

2. Fungal and Bacterial Infections

Specific fungi such as Phytophthora, Pythium, Fusarium, and Rhizoctonia thrive in moist, low-oxygen conditions and are the primary causes of root rot. They invade weakened or dead roots, spread rapidly, and can infect the entire root system. Besides fungi, bacteria such as Erwinia or Pseudomonas can also play a role.

3. Compacted or Poor Soil Structure

Highly compacted soil prevents water from draining properly and blocks oxygen from reaching the roots. Especially heavy clay soils are prone to waterlogging. An overly dense soil structure can also hinder root growth and further weaken the plant.

4. Incorrect Watering

Frequent or excessive watering leads to permanently wet substrate, depriving the roots of oxygen. This is particularly problematic in closed systems such as hydroponics or plant containers without drainage holes.

5. Poor Hygiene and Infected Plant Material

Pathogens can spread through already infected plants, unclean tools, or contaminated substrate. In greenhouses or hydroponic systems, root rot can spread quickly if infected plants are not promptly removed.

Symptoms of Root Rot

Above-Ground Symptoms:

Leaves wilt despite adequate watering.
Leaves turn from green to yellow or brown.
Stunted growth or sudden plant death.
Stem or stalk areas appear mushy or darkened.

Below-Ground Symptoms:

Roots are mushy, slimy, and dark-colored (brown to black).
Roots break easily or dissolve when touched.
A foul odor emanates from the soil or substrate.

Preventing Root Rot

Proper Watering:
- Only water when the topsoil is dry.
- Prefer rainwater or filtered water.
Ensure Optimal Drainage:
- Use well-draining soil.
- Provide drainage holes in potted plants.
- Add drainage materials like gravel or perlite.
Improve Soil Structure:
- Loosen compacted soil or add sand to improve aeration.
- Use raised beds or special substrates for plants sensitive to waterlogging.
Clean Tools and Containers:
- Regularly disinfect pruning shears, shovels, and other gardening tools.
- In hydroponic systems, change and clean water and equipment regularly.
Select Disease-Resistant Plant Varieties:
- Choose plant species that are less prone to fungal infections.

Treating Root Rot

If a plant is already infected, immediate action should be taken:

Gently remove the plant from the soil and examine the roots.
Cut off all affected roots with a sterile knife.
Soak the healthy roots in a fungicide solution or sprinkle with charcoal powder.
Repot in fresh, well-draining substrate.
Adjust watering practices to prevent recurrence.

In cases of severe infection, the plant may need to be discarded to prevent further spread.

Conclusion

Root rot is a serious threat to plants but can be prevented with proper care. A healthy root system is the foundation of a strong plant, so preventive measures are essential. If an infection occurs, quick action can save the plant and prevent further spread.