In the rainy spring climate of Western Washington the magnolia that holds up best is the Star Magnolia or Magnolia stellata. This is a slow growing shrub or small tree with smaller, star-like blooms and hardier than the more common Southern Magnolia with the huge tulip shaped blooms. In zone 7 and 8 of the Pacific Northwest the larger magnolias may survive but it you are growing this southern tree for the blooms you may be disappointed when the rain and late frosts destroy the huge blossoms most springs. The Star Magnolia seems more frost and rain tolerant so in my own garden the flowers have lasted for 3 to 4 weeks on the tree blooming in early spring around mid March.  There may be protected spots near the water or out of the wind where the larger blooming magnolias thrive in Western Washington and to really see how these trees grow visit local arboretums such as the Washington Park arboretum near the UW campus of Seattle. There are also some Southern Magnolia trees growing in the arboretum near the state capitol in Olympia but the climate there is milder than where you garden. Keep growing, Marianne Binetti