Root Rot

What Is Root Rot? Root rot is a condition where a plant's root system decays, typically because the soil is too wet. When potting mix stays saturated, it deprives the roots of the oxygen they need to survive. Without oxygen, the roots cannot function or absorb water and nutrients, which causes the plant to look wilted or drought-stressed even though the soil is wet. As the roots begin to die from lack of oxygen, opportunistic fungi and bacteria naturally present in the soil (like Pythium or Phytophthora) move in and feed on the weakened tissue. This decay spreads upward toward the base of the plant, severing the connection between the roots and the leaves. Signs and Symptoms Lower Foliage Yellowing: The lowest leaves turn pale yellow and eventually brown before falling off. This is one of the earliest signs that the roots are struggling to take up nutrients. Mushy Stems: The stem at the soil line becomes dark and soft. This indicates the rot has moved up from the roots into the main plant structure. Decaying Roots: Healthy roots are typically firm and white or tan. Rotted roots are dark brown or black, slimy, and easily pull apart, leaving behind a stringy center. Foul Odor: The soil smells swampy or sulfurous. This distinct smell is a sign of anaerobic bacteria breaking down the root tissue. Wilting: The entire plant droops and looks thirsty, but the soil is wet. The rotted roots can no longer absorb water to support the foliage. Step-by-Step: How to Treat Root Rot Remove the plant from its pot and gently brush away the wet soil so you can clearly see the root system. Rinse the roots under room-temperature water to wash away remaining soil and get a better look at the damage. Sterilize a pair of pruning shears or scissors with rubbing alcohol to ensure you don't spread bacteria or fungi. Trim away all brown, mushy, or foul-smelling roots. Cut just above the rot into the healthy, firm tissue. Optional: Dip the remaining healthy roots in a solution of 1 part 3% hydrogen peroxide to 3 parts water to help kill any lingering pathogens. Repot the plant into a clean pot using fresh, well-draining soil. Adding extra perlite or pumice will improve aeration and drainage. Wait a few days before watering to allow the freshly cut root ends to dry and heal, which prevents the rot from returning. Best Practices and Pro Tips Improve Soil Drainage: Ensure your potting mix has plenty of aeration materials like perlite, orchid bark, or pumice so water drains quickly. Use Terracotta Pots: Unglazed terracotta is porous and allows the soil to dry out faster than plastic or ceramic pots, which is ideal for plants prone to overwatering. Check Before Watering: Never water on a strict schedule. Always check the soil moisture 2 to 3 inches down before adding more water. Empty Drainage Trays: Never let a plant sit in a saucer of runoff water for more than 30 minutes, as the soil will reabsorb the water and stay saturated. Quick Reference Table Factor | Recommended Range | Why It Matters Soil Aeration | 20% to 30% perlite/pumice | Provides the oxygen roots need to survive and prevents waterlogging. Peroxide Dip | 1 part 3% H2O2 to 3 parts water | Helps kill remaining bacteria or fungi on healthy roots before repotting. Tool Sterilization | 70% Isopropyl Alcohol | Prevents the spread of disease from diseased roots to healthy tissue. Post-Treatment | Wait 3 to 5 days before watering | Gives the trimmed roots time to heal and form a protective callus. Bougainvillea are particularly susceptible to this issue when their environmental needs are not met. While they are resilient drought-tolerant plants in the ground, container-grown bougainvillea require careful monitoring. Cultivars like 'Barbara Karst', 'San Diego Red', and 'Texas Dawn' can quickly show symptoms if root health, lighting, or watering practices are sub-optimal. Common Mistakes to Avoid Reusing Infected Soil: Fungal spores can linger in old soil. Always throw away the soil from a plant that had root rot to avoid infecting other plants. Putting a Small Root System in a Large Pot: After trimming away rotted roots, the plant needs a smaller pot. A pot that is too large holds too much wet soil for the reduced root system to absorb. Fertilizing After Treatment: Do not fertilize a plant right after treating it for root rot. The roots are stressed and cannot process the nutrients, which can lead to fertilizer burn. Only Checking the Topsoil: The top inch of soil may feel dry while the bottom of the pot is still soaking wet. Always check deeper into the pot before watering.