Repotting guide

When & how to repot Western Red Cedar (Thuja plicata)

Also called Western Red Cedar, Giant Arborvitae, Giant Cedar, Pacific Red Cedar.

More about western red cedar

About Western Red Cedar

Thuja plicata · also called Western Red Cedar, Giant Arborvitae · flowering

Western Red Cedar is a majestic, fast-growing conifer native to the Pacific Northwest, one of the most important timber and cultural trees of the region. Its graceful, drooping branchlets carry flat, glossy, aromatic scale-like foliage. Adaptable to a wide range of soils, it makes an excellent large specimen, windbreak, or privacy hedge in zones 5–9.

Mature size: 30–70 m tall in the wild; 15–30 m in gardens; up to 6–8 m wide; fast-growing (30–60 cm per year in good conditions)

Watch for — Windburn and Winter Desiccation: Exposed plants in zones 5–6 can suffer browning of foliage from cold, dry winter winds drawing moisture from foliage faster than frozen roots can replace it. Apply anti-desiccant spray in late autumn; shelter young trees with burlap windbreaks in their first 2 winters.

How to tell western red cedar needs repotting

Repotting on a calendar is less reliable than reading the plant. For western red cedar, watch for these signs:

Thick roots out of the drainage holes, or circling the surface and lifting the plant.
The pot dries out unusually fast and western red cedar wilts between waterings it used to shrug off.
The plant is visibly top-heavy and tips over easily.
Stalled growth and small new leaves over a full season — though with a big specimen, top-dressing is often the better first response before a full repot.

For the underlying biology of a pot-bound root system and why it stalls a plant, see our guide to spotting and fixing a root-bound plant.

How often to repot western red cedar

Every 2–3 years; top-dress in the in-between years. Western Red Cedar's growth habit — broadly conical to columnar evergreen tree; flat, drooping branchlets with glossy, scale-like, pineapple-scented bright green foliage; stringy, reddish-brown fibrous bark; buttressed base in age — sets the pace. Western Red Cedar is a majestic, fast-growing conifer native to the Pacific Northwest, one of the most important timber and cultural trees of the region. Its graceful, drooping branchlets carry flat, glossy, aromatic scale-like foliage. Adaptable to a wide range of soils, it makes an excellent large specimen, windbreak, or privacy hedge in zones 5–9.

What size pot to step western red cedar up to

Move up exactly one pot size. A heavy western red cedar dropped into a vastly bigger pot sits in a reservoir of wet soil its roots cannot reach, which rots them and destabilises the plant. In the years between repots, lift off and replace the top 3–5 cm of soil (top-dressing) instead — it refreshes nutrients without the shock of a full repot.

Not sure of the exact diameter? Our pot size calculator takes the current pot and root spread and tells you the right next size — it deliberately recommends a single step up, never a big jump.

The best time of year to repot western red cedar

Early spring, just as new growth restarts, is the ideal window for western red cedar. The plant is moving into its strongest growth phase and re-roots into fresh soil quickly. Avoid repotting in winter dormancy or, for flowering plants, while it is in bud or bloom — recovery is slowest then and you risk dropping the flowers.

Step-by-step: repotting western red cedar

Consider top-dressing first. If western red cedar is not badly root-bound, scrape off and replace the top 3–5 cm of soil instead — far less shock for a big plant that hates moving.
Get help and one size up. For a full repot, choose a pot just one size larger. A heavy plant needs two people and a stable, free-draining pot.
Ease it out on its side. Lay the plant down, slide the pot off, and gently loosen the outer roots. Do not bare-root a mature specimen.
Repot at the same depth. Add fresh moist, well-drained to moderately wet, slightly acidic loam or clay loam beneath and around the rootball, keeping the original soil line. Firm it so the trunk is stable and upright.
Water and leave it put. Water thoroughly, then leave western red cedar in the same spot and light — moving and repotting at once is what makes it drop leaves.

Aftercare

Leave western red cedar in exactly the same spot and light it was in before — moving and repotting at the same time is what makes a big specimen drop leaves. Water it in well, then let the top of the soil dry before watering again so the larger volume of fresh soil does not stay sodden. Do not fertilise for about 4 weeks — fresh mix already carries nutrients and feeding freshly disturbed roots scorches them.

The right soil mix for western red cedar

Western Red Cedar wants moist, well-drained to moderately wet, slightly acidic loam or clay loam. Highly adaptable to a range of soil types including clay, loam, and sandy loam; tolerates slightly wet soils better than most conifers. Prefers slightly acidic to neutral pH (5.5–7.0). Avoid extremely dry, sandy, or alkaline soils. Good drainage improves disease resistance. Always use fresh mix when you repot — reusing old, broken-down soil reintroduces the compaction and poor drainage you are repotting to fix.

Repotting western red cedar — frequently asked questions

How often should you repot western red cedar?

Every 2–3 years; top-dress in the in-between years for western red cedar. Fully repot western red cedar only every 2–3 years; in the in-between years just top-dress the top 3–5 cm of soil. Step up one pot size in spring with moist, well-drained to moderately wet, slightly acidic loam or clay loam. It is heavy and hates being moved, and a vastly oversized pot holds water against the roots and rots them.

What size pot does western red cedar need?

When is the best time of year to repot western red cedar?

Should you top-dress or fully repot western red cedar?

For a big, heavy western red cedar, top-dressing — replacing the top 3–5 cm of soil — is the gentler option most years, with a full repot only every 2–3 years. A mature specimen sulks and drops leaves when fully repotted, so do it as rarely as the roots allow.

Should you fertilise western red cedar after repotting?

Not immediately. Wait about 4 weeks after repotting western red cedar. Fresh mix already contains nutrients, and feeding freshly cut or disturbed roots burns them. Resume your normal feeding routine once you see new growth.