Northern Whitecedar
Thuja occidentalis · Cupressaceae
📷 Daniel Dumais · CC BY-SA 4.0
⚠️ Feuillage contient thuyone. Chiens, chats : troubles digestifs, irritation muqueuse par ingestion.
The gardener's calendar
In autumn, ease off feeding and take the chance to clean up around northern whitecedar and prepare for winter.
ID card
- Foliage
- Evergreen, flattened scales soft green to copper-brown in winter
- Mature size
- 15 to 20 m tall × 3 to 5 m wide
- Growth
- Slow to moderate, 20 to 30 cm per year
- Hardiness
- Very hardy, -40 °C and below
- Origin
- North America (eastern Canada and United States)
- Soil type
- Well-drained soil, tolerant of moisture and clay
- Form
- Columnar or pyramidal conifer depending on variety
✓ Taxonomy verifiedSource: AI estimate · hardiness: reliability high.
Expert tips
The key tip
Thuja occidentalis grows well but appreciates moist soil, especially when young: water generously in the first year, then gradually reduce. In dry continental climates, mulch to retain summer moisture.
The common mistake
Planting too close together in a hedge (distance <1m) or without initial watering: the plant suffers and doesn't thicken properly.
The pro's trick
Prune lightly each year (May and August) rather than heavy pruning every three years: a Thuja pruned regularly from the start stays dense and compact its whole life.
Care
Sunlight
Thuja occidentalis prefers full sun exposure, with a minimum of 6 hours of direct light daily to maintain dense and vigorously colored foliage. It tolerates partial shade but its form may become less compact. Avoid exposure to drying winds, which can damage foliage in winter.
Watering
Water regularly during the first year after planting to encourage root establishment, then reduce watering once established. During prolonged dry periods, deep watering once a week remains beneficial. In winter, the plant needs no additional water in rainy regions, but ensure good drainage to prevent root suffocation.
Soil and planting
Plant in well-drained, neutral to slightly acidic soil. Thuja accepts moist and even clayey soils, making it very versatile. Improve the soil at planting with compost or peat to encourage establishment. Light mulching protects the shallow roots from temperature fluctuations.
Pruning and trimming
Prune young plants lightly in spring to densify the form, removing dead or malformed branches. Avoid severe pruning that would leave bare areas difficult to fill in. Light annual grooming is sufficient for well-formed mature specimens.
Fertilizing
A moderate application of balanced fertilizer (NPK) in spring at bud break is plenty. Thuja thrives in poor to average soils and doesn't demand abundant feeding. Avoid excess nitrogen, which promotes soft growth and increased pest susceptibility.
Pests and diseases
Thuja may be affected by spider mites in very dry, hot climates, and occasional aphids. Winter browning of foliage, though striking in appearance, is generally not serious. Ensure good drainage to prevent root rot, especially in heavy soil.
Watering
Water regularly during the first year after planting to encourage root establishment, then reduce watering once established. During prolonged dry periods, deep watering once a week remains beneficial. In winter, the plant needs no additional water in rainy regions, but ensure good drainage to prevent root suffocation.
Did you know?
Thuja occidentalis was venerated by Native Americans and early European settlers who called this aromatic tree the "tree of life" because of its rot-resistant wood and recognized properties. Its flattened scales release a distinctly balsamic aroma when crushed, a trait that made it valuable in perfumery and traditional herbalism.
Where to buy it
Best planted in autumn so the roots settle in before summer, or in early spring once the frost has passed. Pick a plant with healthy foliage and roots that are not exposed. Best time: March, October, November.
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Tips generated and checked by Viridia — adapt them to your local climate.