Mature size & growth rate

How big does Korean Arborvitae (Thuja koraiensis) get?

Also called Korean Arborvitae, Korean Thuja.

More about korean arborvitae

About Korean Arborvitae

Thuja koraiensis · also called Korean Arborvitae, Korean Thuja · flowering

Korean Arborvitae is a slow-growing, compact conifer native to Korea and northeast China, valued for its silvery-white leaf undersides and neat pyramidal form. Hardy in USDA zones 5–7, it thrives in full sun to partial shade with consistent moisture and well-drained soil, making it a refined specimen or hedge plant for cooler temperate gardens.

Mature size: 3–5 m tall, 1.5–2 m wide (10–16 ft × 5–6.5 ft)

Indoor size vs how big it gets in the wild

Korean Arborvitae grows on a tree's timeline and scale — indoors it becomes a tall, trunked statement plant rather than a tabletop one. Indoors and in a pot, expect 3–5 m tall, 1.5–2 m wide (10–16 ft × 5–6.5 ft). A pot, your light levels and a little pruning are what set the final size in a home, far more than the plant's theoretical potential.

It gains real height on a trunk or main stem, adding a tier of leaves a year and eventually reaching for the ceiling — this is a plant you grow up, not out.

Growth rate and years to mature

Korean Arborvitae is a slow grower. Realistically, expect a decade or more — slow growers like this add only a few centimetres a year, so expect 8-15+ years to reach their indoor ceiling. Its feeding profile backs this up: apply a balanced slow-release granular fertiliser (e.g. 10-10-10) in early spring. avoid heavy nitrogen feeding, which can promote soft growth susceptible to winter damage. one annual application is typically sufficient for established plants.

Want this turned into the right next pot at the right moment? The pot size calculator and the korean arborvitae repotting guide cover when and how much to size up — pot size is one of the biggest levers on how fast korean arborvitae grows.

How to keep korean arborvitae smaller

You are not stuck with the maximum size. For korean arborvitae specifically, these are the levers, in order of impact:

The decisive tool is the secateurs: korean arborvitae can be topped (cut the main growing tip) to cap its height and force a bushier, shorter shape.
Keeping it deliberately pot-bound in a snug container slows the whole plant and limits ultimate size.
Prune in spring so it heals fast; remove the tallest leader back to a node to reset the height.
Good news: slow growth means topping it once buys you years before it needs doing again.

The keep-it-smaller method, step by step

Pick the new height. Decide how tall you want korean arborvitae and find a leaf node or branch point just below that.
Top the main stem. Cut the main growing tip cleanly just above that node in spring; this permanently caps the height and forces side branches.
Keep the pot snug. Avoid jumping to a much bigger pot — a slightly restricted rootball keeps the whole plant smaller.
Maintain the shape. Prune back the tallest new leaders each spring to hold it at the height you chose.

How to grow korean arborvitae bigger or faster

If you want it to fill the space sooner, push the conditions rather than hoping — for korean arborvitae the accelerators are:

It already wants the bright light it needs; warmth, a yearly pot-up and spring-summer feed are the accelerators.
Pot up a size every year or two while young; restricted roots are the main thing holding height back.
Feed regularly through the growing season and keep it warm — height comes from sustained good conditions.

Light is almost always the ceiling. The korean arborvitae light requirements page covers exactly how bright a spot it needs to grow at its potential instead of stalling.

When korean arborvitae outgrows the room (or the pot)

"Too big" usually arrives as one of these signs for korean arborvitae:

The top leaves pressing against or bent by the ceiling — the classic "this is now too tall indoors" sign.
It has to be moved away from a light source it has literally outgrown.
Roots filling the largest pot you can reasonably keep indoors — at that point it is top-or-prune or move it outside (if hardy).

If it is the pot rather than the room, it is a repotting job, not a goodbye — see the korean arborvitae repotting guide. If you want more of this plant instead of a bigger one, the korean arborvitae propagation guide turns prunings into new plants.

Korean Arborvitae size — frequently asked questions

How big does korean arborvitae get?

Korean Arborvitae reaches 3–5 m tall, 1.5–2 m wide (10–16 ft × 5–6.5 ft) when grown indoors. It gains real height on a trunk or main stem, adding a tier of leaves a year and eventually reaching for the ceiling — this is a plant you grow up, not out.

Is korean arborvitae slow or fast growing?

Korean Arborvitae is a slow grower. Expect a decade or more — slow growers like this add only a few centimetres a year, so expect 8-15+ years to reach their indoor ceiling. Korean Arborvitae grows on a tree's timeline and scale — indoors it becomes a tall, trunked statement plant rather than a tabletop one.

How long does korean arborvitae take to reach full size?

Roughly a decade or more — slow growers like this add only a few centimetres a year, so expect 8-15+ years to reach their indoor ceiling. Light, pot size and feeding move that timeline more than anything else.

How do I keep korean arborvitae smaller?

The decisive tool is the secateurs: korean arborvitae can be topped (cut the main growing tip) to cap its height and force a bushier, shorter shape. Keeping it deliberately pot-bound in a snug container slows the whole plant and limits ultimate size. Prune in spring so it heals fast; remove the tallest leader back to a node to reset the height. Good news: slow growth means topping it once buys you years before it needs doing again.

How can I make korean arborvitae grow bigger or faster?

It already wants the bright light it needs; warmth, a yearly pot-up and spring-summer feed are the accelerators. Pot up a size every year or two while young; restricted roots are the main thing holding height back. Feed regularly through the growing season and keep it warm — height comes from sustained good conditions.