A natural cedar or redwood arbor is pretty low-maintenance. But if you want it to be a crisp white (or another color), skip the paint and coat it with solid stain instead. Solid stain fades over time without blistering and peeling, making for much less of an upkeep hassle down the road.
Sink the Posts Properly: You see them all the time at the garden center: wooden arbors with feet that sit on the ground. These might serve as a trellis for vines or a roof over a freestanding bench, but they won't stand up to the stresses on a fence line or a swinging gate. To take that load, sink the posts 30 to 36 inches below grade, says Pro Fence's Mike McLaughlin, who custom-fabricated and installed the arbor here. Where soil is naturally gravelly, using it to backfill the hole—hand-tamping it every few inches—may provide enough stability and drainage. But where soil is sandy or clay, a better bet is to sink the bottom of the post in 4 to 6 inches of tamped gravel, then fill the hole with a tamped mix of soil and gravel, packing it around the post slightly above grade and sloping it away from the post. Where a post bears the stress of a hinged gate, using concrete helps stabilize it even more. Just be sure to sink the post end in gravel first so it won't stand in water, then fill the hole with a sloped concrete footing. Driving two 12-inch lengths of 1/2-inch rebar through the part of the post to be buried will help keep it anchored. Surround the joint where wood meets concrete with silicone caulk to seal out moisture that could cause the post to rot.