Topping Arborvitae: Effects on Growth Habit

A homeowner asks whether topping arborvitae will encourage lateral spread instead of vertical growth.

Biological Reality

Arborvitae (Thuja species) have genetically determined mature dimensions—both height and width. Topping does not override this programming.

Actual Effects of Topping

• Dense regrowth near cut: Stimulates bushy growth within 1–2 feet of the topping point
• No width increase: Plant will not exceed its natural mature spread
• Permanent deformity: Destroys natural pyramidal form; creates flat-topped, dense crown
• Old wood risk: Cutting into woody, non-leafed sections may leave permanent bare zones

Better Alternatives

1. Select appropriate cultivars: Choose narrow ('Emerald Green', 'Degroot's Spire') or wide ('Green Giant') varieties for the space
2. Light annual shearing: Trim new growth lightly in early summer to maintain density
3. Accept natural form: Arborvitae look best unpruned or minimally shaped

If height is a genuine problem (utility lines, view blockage), consider removal and replacement with a suitably sized species rather than ongoing topping.