American arborvitae(Thuja occidentalis 'Danica')

Overview

Danica dwarf globe arborvitae (Thuja occidentalis ‘Danica’) is a slow-growing, naturally spherical miniature conifer hardy in USDA Zones 3 through 7, holder of the Royal Horticultural Society’s Award of Garden Merit. Selected in Denmark in 1948 by nurseryman Jensen, it is celebrated for its tight, self-contained architecture: growing only 1 to 2 inches per year, it forms a dense, symmetrical evergreen sphere 1.5 to 2 feet tall and wide without requiring any clipping or shearing. Clothed in bright emerald-green, fan-shaped vertical foliage sprays that soften to deep blue-green in winter, ‘Danica’ provides formal geometry in rockeries, border edgings, and entryway planters.

It naturally withstands subzero temperatures down to -40°F (-40°C), making it a bulletproof evergreen for cold northern gardens.

How to Grow

• Hardiness & Climate: USDA Zones 3 through 7. Thrives in cool, temperate summers with steady atmospheric moisture. Performs poorly in the hot, humid Southeast (Zones 8 and 9), where high summer temperatures and night heat cause internal foliage dieback.
• Sunlight: Full sun to partial shade. Minimum 6 hours of direct sun ensures dense outer foliage and prevents thinning.
• Soil & Moisture: Prefers moist, fertile, organically rich loams with neutral to slightly alkaline pH (6.5 to 7.5). Intolerant of severe drought; provide steady irrigation during summer dry spells.
• Winter Wind Protection: While cold-hardy, desiccating winter winds and direct winter afternoon sun can cause foliage tips to brown; shelter from prevailing winter winds in exposed sites.

Landscape Uses

• Formal Low Edging Ribbon: Spaced 18 inches apart on center, spheres form a neat, scalloped green hedge that never requires shearing.
• Entryway Container Spheres: Fits into decorative frost-proof containers to frame front doorways and garden steps.
• Rock Garden Anchor: Sited among granite stones and low alpine perennials to provide permanent winter green structure.

Potential Problems

• Deer Browsing: Like all Thuja occidentalis, foliage is palatable to white-tailed deer; protect with netting or repellents in areas with high deer populations.
• Drought Stress: Shallow roots dry out quickly during hot summer droughts; mulch heavily with organic bark.
• Summer Dieback in the Deep South: Fails south of Zone 7 due to intense summer heat and high humidity.

Frequently Asked Questions

Does ‘Danica’ arborvitae need to be trimmed into a ball?

No. ‘Danica’ is genetically dwarf and naturally forms a tight, dense sphere without any shearing or clipping.

How fast does ‘Danica’ grow?

It is very slow-growing, adding only 1 to 2 inches per year. It takes 10 to 15 years to reach its mature size of 1.5 to 2 feet in diameter.

Does the foliage turn brown in winter?

No. Unlike older arborvitae varieties that bronze heavily, ‘Danica’ retains its rich emerald-to-blue-green color through freezing northern winters.

Companion Plants

Pair Danica dwarf globe arborvitae with flowering perennials and shrubs that contrast with its formal spherical habit:

• Perennial Color Partners: Plant alongside purple coneflowers (Echinacea), Russian sage (Salvia yangii), or catmint (Nepeta).
• Deciduous Flowering Shrubs: Combine with dwarf spirea, roses, or hydrangeas.
• Contrasting Foliage Textures: Underplant with creeping thyme, sedums, or maidenhair ferns in partial shade.

Sources & Lineage

• Missouri Botanical Garden PlantFinder: Record taxon 267837 (Thuja occidentalis ‘Danica’) — Danish origin (1948), growth rate, and dimensions.
• Kew Plants of the World Online (POWO): Thuja occidentalis L. (POWO: 263956-1) — species taxonomy, family (Cupressaceae), and native range.
• Royal Horticultural Society (RHS): Thuja occidentalis ‘Danica’ AGM Profile — Award of Garden Merit evaluation and dwarf conifer garden trials.