Native range
Native to the coastal regions of north-west America in southern Oregon and northern California.
Provenance Choice
No provenance testing has been carried out; seed should be obtained from good British stands or from the natural range. Seed collected from hedges or other horticultural sources should be avoided.
Site Requirements
The species is adapted to warm moist conditions and is not tolerant of exposure. It is a shade tolerant species and in its natural range it maintains a slow but steady rate of growth for several centuries; the timber from older trees is highly valued. It can grow on a wide range of soil types and fertility provided there is adequate (not stagnant) soil moisture within a metre of the surface. However, it is not suited to very poor peats or sites with heavy heather competition; the species appears to have some tolerance of alkaline soils. It is cold hardy throughout Britain and is frost tolerant and withstands moderate pollution. Many British stands have a large number of forked stems.
Pests and Pathogens
Root rot pathogens Phytophthora cinnamomi and P. lateralis are very damaging, and potentially lethal diseases of Lawson cypress. P. lateralis was considered absent from Britain until discovered in Scotland in late 2010. Nursery stock, ornamentals and plantation grown trees are all subject to attack by P. lateralis in the USA where this pathogen is best known. Chamaecyparis is also considered to be particularly susceptible to Armillaria root rot (honey fungus).
Less damaging but also significant, another introduced pathogen, Seiridium canker (Coryneum cardinale) causes scattered twig and branch death on affected trees. Cypress aphid (Cinara cupressivora) is not uncommon as the cause of foliage browning.
Use
The species could find a greater role with climate warming, but the poor stem form and relatively slow growth suggest that it is likely to remain a minor species.
Lawson cypress is categorised as a secondary tree species. These are species that have been planted on a much smaller scale than the principal species but are reasonably well understood and have demonstrated their suitability for forestry in terms of stem form, growth rate and hardiness under current conditions and so have potential for wider use in future.
