Arborvitae vs Western red cedar

In Central Europe thuja hedges are dying on a large scale, for several reasons that reinforce each other. The plant comes from cool, humid sites and cannot cope with hot, dry summers without watering: shoot tips brown and whole branches die. Weakened plants are attacked by the juniper jewel beetle (Lamprodila festiva, also called Ovalisia festiva): its larvae eat the phloem under the bark, a branch or the whole plant suddenly turns red-brown and dies, and oval exit holes are left on the trunk. Nothing works against the larvae under the bark; infested parts can only be cut out and destroyed. Fungal shoot and scale-leaf blights and the thuja bark beetle add to the damage. For these reasons experts no longer advise planting new thuja hedges; yew, privet or a mixed hedge is a safer choice. The dwarf globe forms are the same species and suffer from drought and fungal browning just the same; the jewel beetle mainly goes for exposed, sun-warmed trunks, so it is less common on small globes branched to the ground, but nothing shows that they are immune. In winter frozen soil and wind can brown the foliage, and wet snow splays columnar forms apart.

Western red cedar is not exempt from the problems that are killing white cedar hedges (such as Smaragd) in Central Europe. The juniper jewel beetle (Lamprodila festiva) attacks the whole genus Thuja: its larvae tunnel under the bark, single branches suddenly turn brown and die, and oval exit holes are left in the bark; once the larvae are under the bark there is no effective treatment. Most damage so far has been recorded on white cedar, but the beetle mainly goes for plants weakened by drought, hard pruning or sun-exposed trunks, and western red cedar is distinctly poor at coping with drought and heat, so in hot, dry summers without watering it is just as much at risk. On wet, heavy soil Phytophthora root and collar rot kills it, and the foliage can be browned by cedar leaf blight (Didymascella thujina), especially in dense, damp hedges. Plant it only where the soil stays moist and regular summer watering is possible; a mixed hedge is safer than a long hedge of this one species.