Leyland cypress vs Western red cedar

In the hot, dry summers of Central Europe this shallow-rooted plant easily suffers drought stress, and weakened hedges are attacked by fungal cankers (Seiridium, Botryosphaeria) and shoot dieback (Kabatina, needle blights): whole branches turn brown and there is no effective spray against canker. On waterlogged, heavy soil Phytophthora root rot kills it. Planting too densely and poor air movement make infections worse. It needs watering on frost-free winter days too, because the foliage keeps transpiring. Surfaces cut back into brown wood never green up again, and dead plants leave a lasting gap in the hedge. Old, tall specimens can blow over in storms.

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.