Mature size & growth rate

How big does Emerald Green Arborvitae (Thuja occidentalis 'Smaragd') get?

Also called Emerald Arborvitae, Smaragd Arborvitae, Emerald Green Thuja.

More about emerald green arborvitae

About Emerald Green Arborvitae

Thuja occidentalis 'Smaragd' · also called Emerald Arborvitae, Smaragd Arborvitae · flowering

Emerald Green Arborvitae is one of the most popular narrow, columnar evergreen conifers for hedging and screening, maintaining vibrant emerald-green colour year-round without bronzing in winter. Slow-growing and space-efficient, it is ideal for formal gardens, privacy screens, and small spaces. Thuja foliage contains thujone and is toxic to pets if ingested.

Mature size: 3-4 m tall, 60-90 cm wide at maturity; very slow once established

Indoor size vs how big it gets in the wild

Emerald Green Arborvitae is a tree at heart. Indoors a pot and your ceiling keep it to 3-4 m tall, 60-90 cm wide at maturity, but in the ground it is a different scale of plant entirely (very slow once established). Indoors and in a pot, expect 3-4 m tall, 60-90 cm wide at maturity. In the ground with no restriction it is a completely different plant — very slow once established — 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

Emerald Green 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 in early spring. for hedging use, feeding twice a year (spring and early summer) maintains vigour after regular trimming. avoid high-nitrogen feeds which cause excessively fast, weak growth.

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

How to keep emerald green arborvitae smaller

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

The decisive tool is the secateurs: emerald green 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 emerald green 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 emerald green arborvitae bigger or faster

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

When emerald green arborvitae outgrows the room (or the pot)

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

Emerald Green Arborvitae size — frequently asked questions

How big does emerald green arborvitae get?

Emerald Green Arborvitae reaches 3-4 m tall, 60-90 cm wide at maturity when grown indoors, and far larger where it grows unrestricted (very slow once established). 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 emerald green arborvitae slow or fast growing?

Emerald Green 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. Emerald Green Arborvitae is a tree at heart. Indoors a pot and your ceiling keep it to 3-4 m tall, 60-90 cm wide at maturity, but in the ground it is a different scale of plant entirely (very slow once established).

How long does emerald green 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 emerald green arborvitae smaller?

The decisive tool is the secateurs: emerald green 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 emerald green 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.