Project Guide

How to Build a Garden Arbor

Select Lumber
A wooden garden arbor with trellis sides spans the walkway into a garden.

Rough-sawn cedar is a good choice of lumber for an arbor because of the wood’s natural resistance to the elements. A less expensive option is ground contact pressure-treated lumber, which will hold up to the weather, repel water, resist rot and be painted or stained to a color you prefer.

No matter which variety of wood you choose, it is important that the individual boards of lumber you select are straight and show no signs warping or visible cracks.

You'll need this lumber for the project:

  • Four 10-foot-long, 4-inch x 4-inch posts will support two crossbeams, or top rails.
  • Crossbeams come from two 2-inch x 6-inch boards that are 6-feet-long. Seven rafters are made of pre-cut 2-inch x 2-inch deck balusters, or spindles.
  • A 4-foot x 8-foot section of garden lattice cut in half will provide the sides of the arbor.

Additionally, 2-inch x 4-inch boards will be needed to temporarily brace the structure during installation. You'll need one 8-foot board for each corner and two more that will be cut and used as stretchers bewteen posts.

Mark and Dig Holes
A post hold digger is used to make a hole for the posts of a garden arbor.

The front and rear posts should be spaced 24-inches apart from center.

Mark locations and use a post-hole digger to make holes 30-inches deep for each of the four posts. For the 4-inch x 4-inch posts, each hole should be 10-inches wide to provide sufficient space for the concrete used to anchor the arbor.

Attach Top Rails
A person uses a drill to secure the wood parts of an arbor.

Ornamentation for crossbeams is a personal choice. The ends of the top rails can be cut square at length, at a gentle angle or with a curve before a flat tip. Whichever style you choose, the overall measurement from end to end should be 72 inches.

  • Position two posts on the ground 42 inches apart and place a crossbeam on top of them, flush with the top edge.
  • Center the top rail so that 11 1/2-inches extends beyond the outside edge of each post.

Tip: Use pre-cut 42-inch balusters placed between the posts to help maintain an even distance at the top and bottom while attaching the crossbeams.

  • Drive one 3-inch deck screw through the crossbeam into the left post.
  • Check for square again before using two more screws to secure the top rail to the left post.
  • Use the same method to attach the right side of the crossbeam to the right post.

Next, repeat the process to attach a top rail to the second pair of posts.

Place and Secure Posts into Holes
A person pouring cement mix into a hole to secure posts.

Before using a helper to move the posts to the holes, squarely attach a temporary 2-inch x 4-inch board 30-inches from the bottom of the posts. These stretchers will help stabilize the structure to help keep it square while moving it and also ensure even depth into the holes.

  • Level and plumb the first set of posts in its holes.
  • Be patient to get it right and use stakes and 2-inch x 4-inch boards to brace the posts in position.
  • Insert the second pair of posts into its holes.
  • In addition to making the second pair level and plumb, you must also check for even alignment with the first pair. Use temporary stretchers to help get and keep things straight. Again, be patient to get it right.

Once the posts are plumb and braced, prepare cement mix according to package directions and then carefully fill the holes with it, being careful to remove any air pockets without knocking the arbor out of alignment. Allow the cement to cure according to the manufacturer’s guidelines.

Attach Rafters and Lattice
A white arched garden arbor with lattice on its sides spans a walkway.

After the concrete has cured, attach the balusters to the two crossbeams.

  • Measure and mark each 42-inch spindle 5-3/4-inches from the end.
  • Measure each crossbeam and mark locations for rafters at 9-inch intervals.
  • Place a spindle on a crossbeam, centered on a reference mark and positioned so that 5 3/4-inches extend beyond the crossbeams.
  • Fasten the spindle to each crossbeam with a 3-inch deck screw.
  • Repeat for the remaining rafters.

Lattice can be installed on the two sides of the arbor for added decoration and to give creeping vines a foothold for their upward growth.