If you're short on construction ability, but long on patience, you can create a natural or "verdant" archway with live cedar trees. A staple of formal gardens in the 18th and 19th centuries, trees and shrubs were trained over time to create elaborate living archways, bowers and even summer houses. In its October 1999 issue, Harvard University's Arnold Arboretum's quarterly magazine Arnoldia excerpted the 1870 book "The Art of Beautifying Suburban Home Grounds of Small Extent" by landscape designer Frank Jessup Scott, which describes techniques, still effective today, for training trees--including cedars--into living garden structures.
Plant the cedar trees, according to nursery instructions, several feet apart in the location planned for your arch. Conifer grower Iseli Nursery recommends the blue atlas cedar (Cedrus atlantica Glauca) as a tree often trained to create living fences or archways. According to the U.S. Forest Service, the tree grows quickly when young, and maintains its branches down to the ground. Make sure the trees are set wide enough apart to allow some growth in the plant's width, while still leaving enough room for a wheelbarrow or two people walking abreast to pass between the trees.
Allow the cedars to grow to approximately 12 feet tall each.
Get out your stepladder and measure the distance between the trunks of the trees 8 feet up from the ground. Cut a length of 2-by-4 lumber about 2 feet shorter than the distance between the trees and cut notches on each end.
Tie cedars' main leaders together, using sisal rope, so they bend toward each other. Wedge the notched wooden brace between the trunks of the trees about 8 feet up from the ground. Tie other branches to the brace as desired. Use sisal rope because it biodegrades in about two years (in which time the cedar will have naturally grown together) and will not damage the tree, according to Canadian Gardening magazine online.
Remove the brace in several years when the trees' branches are firmly entwined and the growth pattern is established.
Prune growth between the two trees regularly to maintain the arched shape. Let the outer sides and tops of the trees grow naturally and the two trees will grow back together to form one tree above the arch, or prune into an artificial shape.
Plant several trees in a circle and tie the tops together to "grow" a round garden structure.
It may take years before your arch is complete.