Arbor day: four ways to create beautiful and durable arbors and pergolas

Pool & Spa News, Dec 12, 2005 by Rebecca Robledo

Arbors, trellises and pergolas once had distinct meanings. An arbor, or "tree" in Latin, was used to create shelter.

"Trees and saplings would be bent together to form a structure, and they would then be covered with vines," says Peter Parker, a landscape designer and owner of Classic Design in Santa Cruz, Calif.

Pergolas, which originated in Greece, were flat-topped outdoor rooms. In the 1800s, they became more known for shading walkways. Trellises, on the other hand, provided flat, openwork surfaces on which plants and vines would creep.

Today, some regions assign different meanings to these terms, but they are mostly used interchangeably. An archway marking the entrance to a garden could be called an arbor or a trellis. A beautiful outdoor room, or shaded breezeway with openwork roof, now is known as an arbor or a pergola. These structures generally include openwork of some kind, adding character and textures all their own--from the quaint wood latticework archways to more grand outdoor rooms made of stone.

Whatever you call them, arbors, trellises and pergolas provide lots of versatility. Placed over a hot tub, they create an airy yet cozy shelter. Next to the pool, they make for a restful spot to enjoy the sun. They also shelter outdoor kitchens, dining rooms or entertainment areas, or they can simply frame a view.

Try the following four tips when designing and building arbors, trellises and pergolas:

1 Use human scale.

There are no hard and fast rules for sizing arbors and pergolas. But when it comes to height, landscape designers recommend 8 to 10 feet. "When you go above these numbers, you're getting into monumental scale," Parker says. "Typically, structures that are built in monumental scale tend to de-emphasize the human element."

If you're dealing with some type of pitched roof, the plate height--or lowest point around the edge--should be set at 8 to 10 feet.

Those building in hot climates and expecting the roofs to become solid with plants, should go higher. This gives room for the heat to rise without stifling the users.

2 Calculate shade in advance.

Some arbors and pergolas aren't meant to provide shade. If this is the case, many landscape designers will place rafters at 16 inches apart on center, going in one direction.

On the other hand, if you want to provide shelter from the sun's rays, you will need larger pieces placed closer together.

For example, Clement Butt runs slats perpendicular to the rafters. "They're little tiny strips, maybe 2-by-1-inch, and those could go every foot," says the president of Classic Garden Design, LLC in Weston, Conn. "That gives you quite a bit of shade while still allowing an open canopy."

Keep in mind, shade moves around with the sun. Except for noon, when the sun is directly overhead, part of the area will not be shaded.

"At the beginning and end of the day the shade is going to be quite a bit smaller," Parker says.

If this is not acceptable, track the sun's path. Consider adding some type of shade on the southern and western sides. Or make the structure larger to leave the ideal amount of shade.

3 Provide adequate support for plants.

Some species require more support, while others need a lot of surface to help them attach. This is important when designing an arbor or pergola that will have trailing plants or vines. Grapes and wisteria, for instance, are notoriously heavy and aggressive. Both have sturdy trunks, so the base should be equally solid.

"Wisteria is famous for twisting arbors into pretzels," Parker says. "You need to have strong structural elements--a minimum of 2-by-2-inches."

If you're going to grow wisteria on an arbor against a house, keep it away from the gutters and roofing.

"It'll crawl up the roof and under the shingles within one growing season," says Rick Knight, co-owner of Urban Refinements in Seattle.

Ivy, ficus and trumpet vines are self-supporting, meaning they'll attach to just about anything with their runners or claws. Other vines need a little help. Clematis, for example, needs more surface to grow and attach. "You have to provide a lattice-work or suspended wires on the structure for the vine to attach," Parker says.

4 Build for the long haul.

Even the most delicate arbors need proper support. On his wooden structures, Butt begins with 6-by-6-inch posts on the lightest ones, and moves up to 8-by-8-inches when they get larger. He recommends red cedar rather than white because "it has greater durability."

If you want to save a little money, try pressure-treated posts with red cedar latticework above. These woods look different, so you'll need to cover the pieces with an opaque paint. Butt suggests an oil-based primer and a latex, water-based stain rather than a primer and latex paint. "You'll have much less chipping and cracking," he says.

If you're hiring a carpenter to install the arbor, look for someone who will dowel the wood together. "Nails tend to pull and rust, and the whole arbor will fall apart," Butt says. "The proper way is to have tongue-in-groove or have them doweled on the top and then glued together almost like a piece of furniture." Staples also are a no-no.