Troubleshooting Yellowing Yew After Transplant: Root Rot vs. Environmental Stress

Case Overview

A gardener transplanted two yew trees eight months ago. One thrives; the other yellows and drops needles. The struggling tree was planted in the same potting mix, which had white mold near the bottom of the bag. No scale or other obvious pests were found.

Potential Causes

Phytophthora Root Rot

This soil-borne pathogen thrives in wet, poorly drained conditions. Symptoms include discolored, sparse roots that may fall apart when tugged. The white mold in the potting mix suggests excessive moisture, a precursor to Phytophthora. Confirmation requires digging up the plant to examine roots. If roots are brown/black and mushy, the tree is likely beyond saving and should be removed to prevent spore buildup in the soil.

Environmental Factors

If roots appear healthy (white, firm, extending beyond the root ball), the problem is likely environmental:

• Poor drainage – yews hate "wet feet." Ensure the planting site drains well.
• Soil pH extremes – optimal range is 6.0–7.0. Test with a kit or lab.
• Low fertility – apply a balanced tree/shrub fertilizer.
• Improper watering or insufficient light – adjust accordingly.

Even in the same bed, soil conditions can vary drastically due to construction fill, compaction, or micro-topography.

Recommended Steps

1. Dig up the declining yew and inspect roots.
2. If roots are rotted, remove the plant and avoid replanting yew in that spot.
3. If roots are healthy, correct drainage, test pH, fertilize, and ensure adequate light.
4. Monitor for improvement over the next growing season.

Key Takeaway

White mold in potting mix is a red flag for overwatering. Address drainage first; then investigate other stressors. Yews are resilient if their basic needs—well-drained, slightly acidic soil and moderate moisture—are met.