There are now on the market pressure-treated rot-resistant woods that do
not have arsenic & copper & are environmentally safe. The only part of a
fence that will rot is what comes in contact with the ground, so the more
expensive rot-resistant wood need only be posts, the rest can be
inexpensive fence boards or pickets or whatever.
Wood as a backdrop has a natural beauty & gardens look excellent against
natural unpainted wood; some people hasten the "weathered" look by
slapping on a coat of vinegar which darkens wood nicely. If the rustic
look doesn't appeal, protective whitewashes still reveal woodgrain beauty.
Plastic just never duplicates the beauty of wood, plain or whitewashed.
Vines cling well to wood, not so well to plastic.
However, if it's your plan to paint the whole fence with thick coats of
paint it's going to look the same as a plastic fence anyway. In that case
might as well go with the plastic lumber, as that'd be environmentally
friendly in helping to use up some recycled plastic milkbottles.
-paghat the ratgirl
"Of what are you afraid, my child?" inquired the kindly teacher.
"Oh, sir! The flowers, they are wild," replied the timid creature.
-from Peter Newell's "Wild Flowers"
See the Garden of Paghat the Ratgirl: http://www.paghat.com/