How to Make an Overhead Trellis

A trellis adds character to a patio or garden.

A trellis is usually placed near a climbing plant such as ivy, vines or roses. The trellis provides the vegetation a structure to attach to and eventually climb. An overhead trellis adds a top section to posts, so that the plant creates a cover over an area. Some places you might find an overhead trellis are above a patio or across a path in a garden.

Things You'll Need

• 4-by-4 posts
• Posthole digger
• Gravel
• 2-by-4 boards
• Power saw
• Measuring tape
• Cement
• 2-by-6 boards
• Level
• 4-inch carriage bolts
• Wrench
• 4-inch screws

Instructions

1. Determine the spacing for your four posts and mark their locations with stakes. Use a construction laser to ensure the posts are lined up square.

2. Dig holes for the posts with a posthole digger. The depth of the hole depends on the height of the posts. For an 8-foot high trellis, you need 12-foot-long posts. When burying part of a post, 1/3 of its length is placed in the ground. Dig out an additional 6 inches below the post for gravel to keep water away from the wood. Dig post holes, in this case, 4 1/2 feet deep.

3. Fill the four holes with 6 inches of gravel and tamp it down.

4. Cut 2-by-4 boards into sections 1 foot long. You need 16 pieces. Cut the board sections with a power saw.

5. Place the 4-by-4 posts in the holes. Wedge the 1-foot-long pieces up against the sides of the posts to keep them upright. Use a level to adjust the posts to a vertical position.

6. Mix up a batch of cement according to the directions. Pour the cement into the holes and let the cement dry for two days.

7. Decide which direction you want the trellis beams to face, and then measure the distance between two posts in the opposite direction. For example, if you want the trellis beams to run north to south, then measure the distance between the posts going from east to west. Add 2 feet to the measurement and transfer the length to four 2-by-6 boards. Cut the boards to length with a power saw. Miter the ends to a 45 degree angle if you want a more decorative look.

8. Attach the boards to the top of the posts. Place one board so that it lies flat against the side of two posts running east to west. Raise it so that the edge of the board is even with the top end of the two posts, and use a level to ensure it is horizontal to the ground. Connect it to the posts with 4-inch carriage bolts. Place a second board on the other side of the two posts in the same way as the first so that the two boards sandwich the posts at the top end. Repeat with the other two posts to create parallel supports at the top of the posts. Connect the 2-by-6 boards with 4-inch carriage bolts.

9. Measure the distance between the outside edge of the opposite support beams and add 2 feet to it.

10. Cut 4-by-4s to this length. You can miter the ends if you would like to add a decorative touch.

11. Place the 4-by-4s across the support beams at a perpendicular angle. Space the beams as far apart as you like. The closer they are together; the less light you will get underneath. Anywhere from 12 to 18 inches works well.

12. Toenail 4-inch screws through the inside of the support beams and into cross trellis beams. Toenailing is the process of hammering nails or drilling screws at an angle to connect perpendicular pieces.

References

• University of Minnesota - Sustainable Urban Landscape Information Series; Building Overhead Structures, Pergolas and Arbors; Joanie Somerville, Stephanie Jutila, and Michael Sonnek
• Taylor Rental: Installing a Wood Fence