Rot-resistant woods include redwood, red cedar, Alaskan yellow cedar, and Port Orford cedar, all of which may last a century or more without protection. These woods are easy to work with and they take paint well, but they are soft and dent easily.
Depending on the region of the country, other durable woods may be available. These include high-quality cypress, white oak, and locust. These species offer nearly the same rot resistance as redwood but are much stronger.
Moderately rot-resistant woods include eastern white pine, southern longleaf pine, larch, and swamp oak. These woods may last for many years if they are installed properly and are well-protected with exterior finish.
Slightly resistant or nonresistant woods include alder, poplar, cottonwood, hemlock, the spruces, the maples, red oak, and all other pines and true firs. Do not use these species for exterior trim unless it can be guaranteed that no water ever reaches the raw wood.
Cull Out Defects
Regardless of species, avoid any board containing a large percentage of sapwood, as sapwood is less durable than heartwood. Also avoid boards with splits, surface cracks, or loose knots. These defects will always get worse with exposure to the elements, and provide entry for bugs and fungi.
to read the full Field Guide