Wrigley Field in Chicago is one of baseball’s most recognizable venues, largely due to the iconic green expanse covering its outfield walls. Planted in 1937, this unique horticultural feature instantly sets the park apart from all others in Major League Baseball. The vines transform the hard brick surface into a living backdrop, changing from bright green in spring and summer to deep red and orange in autumn. The wall is home to a combination of plants chosen for their hardiness and ability to thrive in the Chicago climate.
The Primary Vine Identity and Characteristics
The dominant plant species creating the famous green wall is Boston Ivy (Parthenocissus tricuspidata). This clinging woody vine belongs to the grape family and is native to eastern Asia. It is well-suited for covering masonry because it attaches to surfaces using specialized suction-cup-like disks on its tendrils, which do not penetrate or damage the mortar.
The original selection was driven by a desire for an “outdoor, woodsy motif” for the park, not solely for padding. Boston Ivy is deciduous, meaning its leaves fall off seasonally, causing its dramatic color change and eventual bare state during the cold months. This species was chosen partly for its ability to endure the Chicago winters, a major factor in its long-term success on the outfield walls.
The Strategic Dual Planting System
The wall’s full appearance is maintained through a blend of plants, not just the dominant Boston Ivy. A second species was initially planted alongside the Parthenocissus tricuspidata to ensure complete and rapid coverage of the brick. The original planting included Japanese Bittersweet (Celastrus orbiculatus), a fast-growing vine.
Later reports suggest the presence of Virginia Creeper (Parthenocissus quinquefolia), a close relative of Boston Ivy common in Chicago landscapes. Virginia Creeper is distinct because its leaves are divided into five separate leaflets, while Boston Ivy leaves are simple and have three lobes. The dual planting strategy ensures the wall maintains a dense, uniform green aesthetic throughout the season, providing resilience and varied texture.
The Role of the Ivy in Baseball Ground Rules
The ivy-covered wall is not only a decorative feature but also an active component in the unique ground rules of the ballpark. The brick wall itself is not padded; Wrigley Field was grandfathered into an exception to Major League Baseball rules requiring padding on all outfield walls. Although the dense growth appears to offer some cushion, fielders can still be injured when running into the hard surface beneath the vines.
The most famous rule governs what happens when a batted ball disappears into the foliage. If a fair batted ball hits the wall and becomes lodged within the vines, the play is immediately ruled a ground rule double. This awards the batter and all baserunners two bases from their position at the time of the pitch. To signal this ruling, an outfielder must raise their hands to the umpire to indicate the ball is stuck and unplayable.
If an outfielder attempts to retrieve the ball or the ball bounces back out onto the field, it is considered in play, and runners can continue to advance. This creates a high-stakes decision for fielders: immediately signal the unplayable condition for the double, or try to locate the ball at the risk of allowing more runs to score.