Why Is One Arborvitae Producing Excessive Cones While Another Thrives? Water Stress vs. Insect Galls

Two sets of arborvitae planted two years ago—one on a hill, one on flat ground. The hillside plants are loaded with small green "pods" (cones) that weigh down branches; the others are fine. The hillside plants get faithful watering.

Cones Indicate Stress

Heavy cone production is a classic stress response. On a 2-year-old plant, the most likely cause is water—too much or too little.

Diagnose the Real Issue

• Check cone uniformity. True cones look alike. Irregular, lumpy growths are insect galls.
• If galls: Spray Acephate every 3–4 weeks from new growth through fall, or drench with Imidacloprid once in winter for season-long control.
• If cones: Next spring, lightly shear off the cones as they form to prevent branch drooping.

Watering on a Slope

Hillside plants dry faster. Even with regular watering, they may need more frequent, deep soakings to match the flat-site plants.