Reviving Browning, Thinning Arborvitae

Eleven-year-old arborvitae (Thuja occidentalis) show browning tips and thinning interior. Possible causes:

• Shade: Arborvitae thin in low light.
• Winter burn: Desiccation from wind/sun on frozen ground.
• Overwatering/poor drainage: Roots suffocate in soggy soil.
• Pests/disease: Spider mites, bagworms, or fungal blights (e.g., Phomopsis).
• Age/natural aging: Interior needles shed; 'Techny' and 'Emerald Green' open up after 10–15 years.

Action Plan

1. Inspect: Check for mites (tap branches over white paper), bagworms, or fungal spots.
2. Prune: Remove dead/brown tips; lightly shear to encourage dense growth (avoid cutting into bare wood).
3. Soil test: Check pH and drainage; improve with compost if heavy clay.
4. Water: Deep, infrequent watering; avoid constant moisture.
5. Fertilize: Apply balanced slow-release fertilizer in early spring.
6. Consult extension: Local university extension can diagnose region-specific issues.

Regular light pruning every few years maintains density and reduces interior browning.