Thuja and Arborvitae

How to choose a thuja

The Emerald Green Arborvitae, also sold as Smaragd, is a narrow column of bright green foliage that reaches 3 to 4 metres high and about a metre wide. It keeps its shape with almost no trimming and is the usual choice for a formal hedge, a pair at an entrance or a vertical accent.

The Golden Biota and the Morganii Oriental Arborvitae are compact oriental arborvitae, botanically Platycladus, with golden foliage held in upright fans. Both are slow, stay small for many years and take more heat than the other thujas.

The Western Red Cedar is a different proposition: a large forest tree from north west America that can pass 20 metres in a cool, moist district. It belongs on a big property as a specimen, shelter belt or tall screen. The Fastigiata Western Red Cedar is a narrower form of the same tree, better suited to a tall hedge or a line along a boundary.

Where thuja works

Emerald Green suits cool temperate and mild temperate climates, including Tasmania, Victoria, Canberra, the tablelands and the Adelaide Hills. It is fully frost hardy but scorches in hot, dry wind and is not a plant for the subtropics. Western Red Cedar needs the same cool conditions with reliable moisture and deep soil. The golden oriental types are the adaptable ones, growing well from cool districts through warm temperate gardens and into the milder subtropics, provided the drainage is good.

All want full sun for dense growth, and the golden forms colour most strongly in sun. For other shapes and textures, see our conifers, the conifers for formal gardens and the junipers, which cope with drier soil.

Planting and spacing

Plant in autumn or spring into well drained soil improved with compost. For a hedge of Emerald Green, space plants 60 to 80 centimetres apart. Set the Fastigiata Western Red Cedar 1 to 1.5 metres apart for a tall screen, and give a specimen Western Red Cedar at least 8 metres clear of buildings, pipes and other trees. The compact golden types need about a metre each, or one to a large pot. Mulch well and keep the mulch off the trunk.

Care basics

Water deeply and regularly for the first two summers. Thuja have shallow, fibrous roots and brown from the inside if they dry out, so a mulch layer and a weekly soak in hot weather matter more than fertiliser. A slow release feed in spring is enough.

Clip little and often, from spring to early autumn, and take only the green tips. Never cut back into bare brown wood, because thuja does not reshoot from it and the gap stays for good. Start shaping a hedge while it is young instead of trying to reduce it later. Thuja is mildly toxic if eaten, so put the clippings in the green bin, not where animals graze.

Common questions

How fast does Emerald Green thuja grow?

Steadily, at about 20 to 30 centimetres a year once established, in good soil with regular water.

Why is my thuja going brown inside?

Some inner browning in autumn is normal shedding of old foliage. Browning at the tips usually points to dry roots or hot wind.

Can I cut a thuja hedge back hard?

No. It will not regrow from old brown wood, so trim lightly and regularly into green growth only.

Will thuja grow in a pot?

The compact golden types and Emerald Green do well in a large pot with quality mix and steady watering.