The ivy-covered outfield walls at Wrigley Field have been a fixture since the 1930s, making the ballpark one of the most recognizable venues in sports history. This unique wall of dense vegetation creates a picturesque backdrop for baseball games. It represents a living part of the stadium’s architecture, softening the hard brick surface beneath and introducing its own set of rules into the game.
Identifying the Iconic Wrigley Field Vine
The verdant tapestry on the outfield walls is composed of two distinct types of clinging vines. The primary covering is Boston Ivy (Parthenocissus tricuspidata), a vigorous climber that provides the majority of the dense foliage seen throughout the summer. This vine is identifiable by its glossy green leaves that are typically simple and three-lobed.
Interwoven with the Boston Ivy is the Virginia Creeper (Parthenocissus quinquefolia), a native North American plant. This second species is distinguished by its compound leaves, which are composed of five separate leaflets radiating from a central point. The combination is practical: Boston Ivy offers dense coverage, while Virginia Creeper is hardier and contributes resilience. Both species belong to the grape family (Vitaceae) and are not “true” ivy.
How the Vines Thrive and Cling
These vines adhere to the brick surface without damaging the wall by utilizing a specific biological mechanism for attachment. Instead of using root-like aerial roots, which can compromise mortar, both Boston Ivy and Virginia Creeper climb using specialized tendrils. These tendrils feature small, disc-shaped pads, often referred to as holdfasts or sucker disks, at their tips.
The disks secrete a mucilage that acts as a powerful adhesive, gluing the vine securely to the brick. This self-clinging method allows the vines to cover the wall while minimizing structural harm to the masonry. The vines are deciduous, meaning their leaves turn scarlet in the autumn before being shed for the winter season. This annual leaf drop is an adaptation to survive the Chicago winters and allows the brick to absorb solar heat.
Rules and Game Play Interactions
The dense vegetation on the outfield wall requires specific ground rules for game play at Wrigley Field. These rules address situations when a batted ball becomes lost within the thick mass of vines. If a fair batted ball hits the wall and becomes permanently lodged in the ivy, the umpire immediately calls a dead ball.
The lodging results in an automatic ground-rule double, awarding the batter and all runners two bases. Fielders are discouraged from attempting to retrieve a lodged ball, as the play is considered live if they reach into the vines. The ivy also provides natural padding over the hard brick, allowing the stadium to be grandfathered into not requiring standard padded outfield walls.