There is long-standing confusion in taxonomy and nomenclature of Japanese flowering cherries and apricots but, to make a confusing story short---yes, both varieties you mention will do well in the Seattle area. In fact, both can be seen at the Washington Park Arboretum.
For hours, locations, etc. visit the Arboretum website.

Season All Season
Date 2008-01-31
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The peak season for Rhododendron blooms would probably be May, but there are Rhododendrons which bloom earlier and later than this as well (March through June). For more detail about which species bloom at what time, you may find this link to Oregon State University's Landscape Plants web site of interest.

From the Washington Park Arboretum's list of plants at their peak:

March: Camellia, flowering cherry, corylopsis, daphne, forsythia, heather, hellebore, magnolia, rhododendron, witch hazel.

April: Azalea, barberry, camellia, flowering cherry, halesia, maple, madrona, magnolia, rhododendron, serviceberry.

May: Crab apple, dogwood, magnolia, mountain ash, rhododendron, red bud, serviceberry.

June: Rock roses, brooms, Korean dogwood, rhododendron, stewartia, styrax

Season Summer
Date 2007-02-28
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The Washington Park Arboretum has many examples of Hamamelis mollis, or Chinese witch hazel (unless you meant Corylopsis sinensis or Loropetalum chinense, which also go by the common name 'Chinese witch hazel'). Kalmia latifolia (Mountain laurel) and Fothergilla (but not Fothergilla gardenii, which is Witch alder) are also in the Arboretum. The variegated kiwi, Actinidia kolomikta, used to be grown here at the Center for Urban Horticulture. Soft shield fern, or Polystichum setiferum, may be in the Arboretum, but is not listed, as it is not a woody plant. I consulted The Woody Plant Collection in the Washington Park Arboretum (not up-to-date, as it was published in 1994), so in some cases the plants may no longer be where they once were listed on maps. The trail map linked here only provides information on large collections of plants, but the book provides their location on a grid. You could go to the Arboretum and ask for assistance in locating the witch hazels (some are in the Witt Winter Garden, and others are in a grove on the south end of the park) and other plants.

All of these plants grow well in our area. I have a dwarf form of Fothergilla in my garden, and it has been thriving. I have also seen many of the other plants in your list growing happily in private gardens in Seattle. Since you wish to know what they look like, here are several links to additional information with pictures.

Hamamelis mollis picture 1
Picture 2
Picture 3
Picture 4

Fothergilla gardenii Picture 1
Picture 2

Kalmia latifolia Picture 1
Picture 2

Polystichum setiferum Picture 1 (from a local gardener)
Picture 2

Season All Season
Date 2007-07-12
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