As much as we at Horticulture love trees for providing shade (and so much more), there are times when a tree is not the best fit. (Or a tree is a great fit, but the one you planted needs a whole bunch of years to grow before it casts an ample shadow.) An arbor or pergola can be the perfect answer for instant cooling shade over a patio, walkway or other garden space.
Pergola vs. Arbor
What's the difference between these structures?
Usually the word arbor is used to describe a structure that has two to four supporting posts and a slatted roof that can be flat or arched. On four-posted arbors, two of the sides are often closed with latticework or horizontal bars. Typically an arbor is a smaller structure, big enough to fit a single bench or small table with two chairs.
A pergola is more substantial, with four or more supporting posts spaced wide enough to fit a full outdoor dining table or conversation set. All sides of a pergola are open, and the roof is usually a grid.
Advantages of Arbors and Pergolas
Whether you choose a pergola or an arbor will depend on the size of the space and the role of the structure. A pergola is a better choice for covering a patio that will host friends and family, but an arbor can suffice for an outdoor reading nook.
These structures are valuable in the garden because of the shade that they cast. Because their tops are slatted, they create bright, cooling shade while also allowing hot air to rise and escape. The slats create a pattern of shadows, but if you want solid shade, you can cover a portion of a pergola's roof with light-colored shade cloth.
Both pergolas and arbors can also host climbing plants, which will add interest, soften the structure's lines and deepen the shade, if allowed to cover the top of the structure.