Why Three Arborvitae Planted Together Grow at Different Rates

Three arborvitae planted 10 feet apart show vastly different growth after three years: one large and bushy, one medium, one stunted. The site previously had a large pine tree. Several factors can cause such disparity.

Possible Causes

• Cultivar differences: Were all three the same variety? Different cultivars (e.g., 'Emerald Green', 'Green Giant', 'Techny') have vastly different growth rates and mature sizes.
• Root competition: Remnants of the pine's root system may still be competing for water and nutrients, affecting nearby plants unevenly.
• Soil variability: Micro-differences in soil depth, compaction, pH, or drainage across the planting area.
• Light exposure: Even slight shading differences (from structures, trees, or each other) impact growth.
• Water distribution: Irrigation or rainfall may not reach all plants equally, especially on a slope.
• Planting quality: Root ball handling, planting depth, and backfill soil can vary per plant.

Diagnostic Steps

1. Verify cultivar labels or receipts.
2. Conduct a soil test for each planting spot (pH, nutrients, texture).
3. Check soil moisture at root depth (12–18 inches) for each plant.
4. Inspect root flares: ensure they're at or slightly above grade, not buried.

Addressing identified issues (fertilizing, irrigating, adjusting pH) can help the lagging plants catch up.