A willow pergola enhances the appeal of an outdoor landscape. This decorative yet functional gardening structure supports trailing vines and provides cool shade during the summer months. Weave willow branches to form the top of the pergola, and mount it over four colonnades. Install it near your home, or atop a small mound or hill that overlooks a lake and place a bench underneath for a relaxing space.
Stand a willow post vertically over the ground and pound it in 8 inches deep. Hammer each of the seven remaining posts into the ground in the same way, forming a straight line that covers a 6-foot area. Space each post 8 inches apart.
Hold a thinner willow branch next to a corner post, an inch above the ground. Leave 2 inches to extend from the post and weave it over the corner post, extending the remaining length to the adjacent post. Weave it under this post, and extend it to the one next to it. Continue this process of weaving it over and under adjacent posts till you reach the end. If it falls short during the weave, simply hold another branch flush against it and continue till the end post to form one row.
Repeat the process of weaving a row over the previous one, but start by placing a branch under the corner post as opposed to over it (as in Step 3). Continue the process until you form a second row, and repeat the process of weaving until you reach the height of the posts.
Weave smaller branches to fill any visible gaps between posts.
Cut the posts at ground level with loppers and lay the woven artwork on the ground carefully. Trim uneven or excess branches off until you have a 4 foot wide and 6 foot long willow roof. Pull out the remaining lengths of willow stakes from the ground and discard.
Dig holes for the colonnades, the posts that will hold the willow roof in place. Measure and mark four points over the selected area to form a 6- by 4-foot grid. Dig a 10-inch deep hole over each point, as wide as the colonnades.
Mix mortar with water in a wheelbarrow. Add 6 inches of mortar into each hole before standing a colonnade vertically over it. Pack each hole with dirt to hold the colonnades securely.
Lay the two girders over two colonnades and hammer nails in to hold in place. Spread the willow roof over the girders. Hammer nails to attach each of the eight willow posts to the girders.