Mature size & growth rate

How big does Japanese Arborvitae (Thuja standishii) get?

Also called Japanese Arborvitae, Standish's Arborvitae.

More about japanese arborvitae

About Japanese Arborvitae

Thuja standishii · also called Japanese Arborvitae, Standish's Arborvitae · flowering

Japanese Arborvitae is a graceful, slow-growing conifer native to subalpine forests of Japan's Honshu and Shikoku islands. Its flat, bright green aromatic foliage sprays and broadly pyramidal form make it an elegant specimen tree. Rarely seen in Western cultivation, it prefers cool, moist conditions and well-drained soils, and is one parent of the popular 'Green Giant' hybrid.

Mature size: 6–10 m tall, 2–4 m wide in cultivation; up to 18 m in habitat; slow-growing (15–25 cm per year)

Indoor size vs how big it gets in the wild

Japanese Arborvitae is a tree at heart. Indoors a pot and your ceiling keep it to 6–10 m tall, 2–4 m wide in cultivation, but in the ground it is a different scale of plant entirely (up to 18 m in habitat; slow-growing (15–25 cm per year)). Indoors and in a pot, expect 6–10 m tall, 2–4 m wide in cultivation. In the ground with no restriction it is a completely different plant — up to 18 m in habitat; slow-growing (15–25 cm per year) — which is why the pot, the light and the pruning matter so much for the size you actually end up with.

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

Japanese 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: light annual feeding is sufficient. apply a balanced slow-release granular fertiliser in early spring. japanese arborvitae is slow-growing and does not require heavy nutrition. overly fertile soils can promote rank, soft growth. established trees growing in good garden soil rarely need supplemental feeding.

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

How to keep japanese arborvitae smaller

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

The decisive tool is the secateurs: japanese 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 japanese 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 japanese arborvitae bigger or faster

If you want it to fill the space sooner, push the conditions rather than hoping — for japanese 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 japanese arborvitae light requirements page covers exactly how bright a spot it needs to grow at its potential instead of stalling.

When japanese arborvitae outgrows the room (or the pot)

"Too big" usually arrives as one of these signs for japanese 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 japanese arborvitae repotting guide. If you want more of this plant instead of a bigger one, the japanese arborvitae propagation guide turns prunings into new plants.

Japanese Arborvitae size — frequently asked questions

How big does japanese arborvitae get?

Japanese Arborvitae reaches 6–10 m tall, 2–4 m wide in cultivation when grown indoors, and far larger where it grows unrestricted (up to 18 m in habitat; slow-growing (15–25 cm per year)). 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 japanese arborvitae slow or fast growing?

Japanese 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. Japanese Arborvitae is a tree at heart. Indoors a pot and your ceiling keep it to 6–10 m tall, 2–4 m wide in cultivation, but in the ground it is a different scale of plant entirely (up to 18 m in habitat; slow-growing (15–25 cm per year)).

How long does japanese 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 japanese arborvitae smaller?

The decisive tool is the secateurs: japanese 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 japanese 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.