Flowering or fruit-bearing plants gracefully climbing a wooden framework bring a three-dimensional touch to your landscape design. Along an exterior wall, a trellis can give plants maximum exposure to the sun, shield them from extreme weather, or provide privacy for a pool or a patio. Freestanding post-and-beam arbors control and support heavy, spreading vines like grapes and wisteria and at the same time add a touch of classic design.
Mount lightweight wood or plastic trellises at least 2 inches from the house with wooden spacers. The gap lets air circulate and helps prevent vines from attaching themselves to the wall. Erect sturdier trellises intended for bushy plants at least 6 inches from the wall.
If you want an arbor that is big enough to walk under, build it at least 4 feet wide and 7 feet high, with beams and rafters overhanging the corner posts at least 1 foot on all sides. Choose a site for the arbor that is level and use the squaring method described on page 188 to locate the corner posts.
Trellises and arbors must be strong enough to support mature plants in full bloom and to withstand the worst weather your region offers.
Rot-resistant redwood or cedar are excellent choices for trellises and arbors. Neither requires painting or sealing as ordinary pine does. And unlike pressure-treated lumber, they contain no preservatives harmful to some plants. No matter what material you choose, assemble the structure with corrosion-resistant galvanized nails and other hardware.
Choosing a trellis
A simple trellis starts with a pair of 2-by-4 uprights, located parallel to a wall or at right angles to it and set at least 2 feet into the ground. A trellis to support light vines (above, left) begins as a rectangular frame of 2-by-4s nailed to the posts, flush with the tops. The frame should be 1 foot shorter than the height of the posts and at least 2 feet wider than the distance between them. You can weave ¼- by 2-inch lath into a uniform grid (inset) or buy basket weave lattice and cut it to fit the frame. For heavier vines, a grid of 1-by-2s (with the posts serving as two of the verticals) provides sturdy support (above, right). Spacers that are made of 1-by-2s and sets of hooks and eyes hold the trellis 6 inches from the wall. You can cut and hinge the posts (inset) about 6 inches from the ground to permit tipping the trellis outward for pruning the vines or painting the house.
Setting the posts
For each 4-by-4 corner post, dig a hole 3 feet deep with a spade or posthole digger. In soft or sandy soil, place a flat stone or brick at the bottom of each hole. Stand a post in the center of a hole with the sides aligned to the rectangular layout. While a helper uses a level to hold the post vertical (right), tamp soil around the post with a 2-by-4 in successive layers a few inches deep until the hole is filled. To keep the post plumb, temporarily nail two braces to the post and to stakes in the ground. When the first post is in place, stand the other posts alongside it one at a time and mark them at the height of the first. Turn the posts over, then set and brace them in the remaining holes to the depth marked.
Mounting the beams
Measure and cut four 1-by-8s for the beams. With a helper, lift a board even with the top of one pair of posts, the ends extending equally. Fasten the board to one post with a nail, then level the board and nail it to the other post. Mount a second on the posts’ opposite sides. Drill two ½-inch holes through the boards and post, 1 inch from post and board edges (inset). Insert 6-inch carriage bolts and secure with flat washers and nuts. To complete the beam, cut 7½-inch-long spacers from 4-by-4 post lumber. Nail the spacers between the boards at 12- to 18-inch intervals, flush with the top and bottom edges. Build a similar beam on the other two posts.
Installing the rafters
Measure and mark rafter positions on top of the beams at 18- to 24-inch intervals, then cut 1-by-6 boards for the rafters. Set each rafter on edge across the beams, aligned with the marks and overhanging the beams equally on each side. Toenail the rafters to the beams (right), or use galvanized rafter ties (inset). To prevent splits from occurring when toenailing along the edge of a board, drill pilot holes at the correct angle slightly smaller than the diameter of the nails.