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Root rot
Pythium spp., Phytophthora spp., Rhizoctonia solani
Root rot is a fungal and water mould disease that kills plant roots in waterlogged soil, causing wilting, yellowing, and plant death. Pythium, Phytophthora, and Rhizoctonia are the main pathogens. Prevent it with good drainage and avoid overwatering; once established, the infection persists in soil for years, making early detection and improved growing conditions essential.
Root rot is a common problem in UK gardens caused by soil-borne fungi and water moulds such as Pythium, Phytophthora and Rhizoctonia. It thrives in wet, poorly drained soils, attacking roots and leading to wilting, yellowing and plant death. You can prevent it with good drainage and cultural care, and manage outbreaks by improving conditions and sanitation. Early detection saves plants; once advanced, recovery is tough as pathogens persist in soil for years.
Worsens after prolonged wet weather, peaking in warm, humid summer months.
- •Prevent with sharp drainage and measured watering.
- •Spot early: wilting plus mushy dark roots.
- •Trim and repot in sterile mix for recovery.
- •Sanitise tools to halt spread.
- •Beneficial microbes offer organic protection.
- •Avoid overwatering in our damp UK climate.
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How to identify
Look for stunted growth and wilting despite watering. Dig gently to check roots: healthy ones are white and firm; rotted roots are soft, dark brown to black, and slimy, often with a 'rat-tail' appearance where the outer layer slips off. Pythium causes wet, disintegrating roots; Rhizoctonia gives drier, tan-brown rot with web-like hyphae at 90-degree angles near the soil line. Stems may show brown lesions just above soil level. Lower leaves yellow or droop first.
Damage and symptoms
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Affected plants wilt in warm weather, even when soil is moist, with sparse, unhealthy foliage. Roots decay from tips inward, losing fine feeder roots essential for water uptake, causing drought-like symptoms. Severe cases girdle stems at soil level, killing the plant. Over time, whole beds collapse with yellowing, stunted growth and dieback. Secondary pests may invade weakened roots, worsening damage.
Lifecycle
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These pathogens live in soil as spores or sclerotia for years, spreading via water splash, tools, pots or infested debris. They infect stressed roots in wet conditions; Pythium and Phytophthora favour saturated soils, Rhizoctonia prefers warm, moist but not waterlogged. Activity peaks in warm spells; spores activate with excess moisture, multiplying rapidly in poor drainage.
Most affected crops
Prevention
Improve drainage
Use gritty compost in pots and raised beds in open ground. Avoid low spots where water pools. Add sharp sand or grit to heavy clay soils in autumn to enhance drainage before planting.
Water wisely
Water deeply but infrequently, allowing topsoil to dry between sessions. Mulch to retain moisture without sogginess. Check soil moisture with your finger before watering.
Choose right plants
Pick resistant varieties where available, like certain tomato rootstocks. Avoid overcrowding to ensure air circulation and quick drying after rain.
Sanitation first
Clean tools, pots and boots with diluted bleach or alcohol between uses. Discard badly affected plants and don't compost them.
Organic control
Remove infected roots
Unpot or dig up affected plants. Trim away all rotted roots with sterilised secateurs, cutting into healthy white tissue. Rinse roots in hydrogen peroxide solution if needed.
Repot in fresh mix
Use sterile, well-drained compost with added perlite. Treat roots with beneficial microbes like Trichoderma or Bacillus subtilis drenches before replanting.
Boost soil biology
Apply mycorrhizal fungi inoculants at planting to outcompete pathogens. Encourage worms and beneficial microbes with organic matter, but avoid fresh manure.
Dry out the soil
Let soil dry thoroughly between waterings to starve fungi. Improve airflow around plants to speed evaporation.
Chemical control
Fungicide drenches
Use approved products containing metalaxyl or propamocarb for Pythium/Phytophthora as soil drenches on ornamentals, following label rates. Rotate to avoid resistance.
Targeted applications
Apply protectant fungicides like those with azoxystrobin pre-planting in high-risk beds. Check current UK approvals via AHDB as formulations change.
Companion plants and deterrents
Frequently asked
Can I save a plant with root rot?
Yes, if caught early. Trim rotted roots, repot in fresh gritty compost and withhold water until recovery. Success depends on how much healthy root remains; severe cases rarely recover fully.
Why does root rot keep returning?
Is root rot worse in pots or open ground?
Pots are riskier due to trapped water. Ensure pots have drainage holes and saucers empty fully. Open ground improves with organic matter to boost drainage.
Does mulch help prevent root rot?
Yes, coarse organic mulch like bark reduces soil splash and weeds, but avoid thick layers on wet soils as they hold moisture. Use sparingly in rainy periods.
How do I test for root rot?
Gently unearth roots; if they mush easily, smell foul and lack firmness, it's likely rot. Confirm by absence of pests or other issues like drought stress.
Grow with confidence
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