Western redcedar roots are extensive. Tap roots are poorly defined or nonexistent, but fine roots develop a profuse, dense network. Root systems tend to be shallower and less extensive on wet soils than on deep, moderately dry soils. Cones average about three to six seeds, but cones are often numerous and heavy seed crops are common. The seeds are dispersed primarily by wind.
Germination is epigeal.
Stratification may improve the germination of some dormant seed lots. Of all conifers in the northern Rocky Mountains, western redcedar and western hemlock seedlings grow the slowest. Western redcedar grows best in maritime climates with cool, cloudy summers and wet, mild winters. In drier areas west of the Cascades, western redcedar becomes abundant only on wet sites such as ravines, along streams, or on poorly drained bottomlands. Western redcedar is not resistant to frost and is sometimes damaged by freezing temperatures in late spring or early autumn.