Root rot is a serious hydrangea condition: roots are deprived of oxygen and decay. Often unnoticed until distress, it quickly leads to decline or death.
Causes of Hydrangea Root Rot
Hydrangea root rot is caused by a lack of root oxygen. Excessive watering saturates soil, displaces air, and prevents oxygen absorption. This leads to decay, called ‘wet feet’.
Poor soil drainage also contributes to root rot. Heavy clay or low-lying areas trap moisture, creating anaerobic conditions. Preventing air circulation, this fosters harmful pathogens.
Fungal pathogens thrive in wet, oxygen-deprived conditions. Attacking weakened roots, they accelerate rot. Rhizoctonia and Fusarium also cause root rot.
Identifying Root Rot Symptoms
Foliage changes are first signs of root rot: leaves yellow, brown, or wilt, even in moist soil. Damaged roots cannot absorb water/nutrients, causing wilting and mimicking drought.
Growth may be stunted/slow. Hydrangeas show reduced vigor (smaller leaves, thinning canopy). Reduced growth results from compromised root system.
Stem base near soil line may be discolored, dark, or mushy. Healthy roots are firm, white/tan. Rotted roots are dark brown/black, soft, mushy, often foul-smelling.
Preventing Root Rot in Hydrangeas
Hydrangeas prefer moist, well-draining soil. Water deeply, allowing top inch or two to dry. Morning watering is best; foliage dries before nightfall, reducing fungal risk. Soaker hoses or drip irrigation direct water to root zone, minimizing leaf wetness.
If your garden has heavy clay, amend with organic matter to improve drainage/aeration. For poor drainage, consider raised beds or containers with drainage holes to prevent water pooling.
- Choose a location with well-draining soil and appropriate sun (morning/afternoon shade) to prevent wet soil.
- Ensure proper spacing for air circulation.
- Plant hydrangeas at correct depth, root ball level or slightly above soil.
- Apply 2-3 inches of organic mulch to retain moisture, regulate temperature, keeping it a few inches from the stem to avoid trapping moisture near crown.
Treating Hydrangea Root Rot
Early intervention improves chances of saving the hydrangea. Ignoring initial signs can lead to rapid decline.
For container hydrangeas, remove from pot. For in-ground plants, gently dig up, preserving root ball. Inspect roots thoroughly, identifying soft, black, or mushy areas (signs of rot). Remove waterlogged, foul-smelling soil.
Using sterilized pruning shears, trim diseased roots. Make clean cuts into healthy, white root tissue. Sterilize tools to prevent pathogen spread. If significant roots are removed, prune back foliage/stems to reduce stress, allowing focus on new root growth.
Repot container hydrangeas into fresh, well-draining potting mix with ample drainage holes. For in-ground plants, relocate to a new site with improved drainage and soil, or extensively amend existing soil before replanting. When replanting, spread healthy roots, backfill with appropriate soil, setting plant at correct depth.
Adjust watering to deep, infrequent applications, letting soil dry. Avoid over-fertilizing, which stresses plants. Monitor for recovery (new, healthy leaf growth). Fungicides are generally not standalone, but systemic types can be used for severe cases, following instructions and with improved cultural practices. Continued observation and environmental adjustments are necessary for long-term health.