Ornamental grasses have become a popular feature in modern landscaping, offering texture, movement, and a strong vertical element to garden designs. These plants, which belong to the Poaceae family, range dramatically in size, from small tufted varieties to massive specimens used as screens or focal points. When selecting a variety, the final height is often the deciding factor for gardeners looking to maximize visual impact.
Identifying the Tallest Ornamental Grass
The tallest ornamental grass is Arundo donax, commonly known as Giant Reed or Spanish Reed. This massive perennial grass typically reaches heights between 20 and 33 feet under ideal growing conditions, making it one of the largest herbaceous plants in the world. Its sheer size sets it apart from all other widely cultivated ornamental varieties.
The plant’s physical structure is reminiscent of bamboo, featuring thick, hollow, cane-like stems, or culms, that are sturdy. Its leaves are broad, grey-green, and sword-like, growing rapidly to support the plant’s height. The growth rate is exceptional, with the plant capable of adding several inches of height per day in peak season. In late summer, the Giant Reed is topped by large, feathery plumes that transition from soft tan to silvery-white.
Cultivation Requirements for Maximum Height
This species thrives in full sun exposure, requiring six or more hours of direct light daily to fuel its rapid growth. The grass naturally occurs in riparian zones, meaning it demands consistently moist or even wet soil conditions. While it tolerates a wide variety of soil types, it performs best in fertile, well-drained loamy soil that retains moisture. The application of fertilizer can increase the plant’s biomass and overall height, though it is not always necessary in rich soils. Arundo donax is hardy in USDA Zones 6 through 10, requiring mild winters to survive and flourish. The plant’s aggressive growth habit is a consideration, as it spreads vigorously through tough, fibrous underground rhizomes. Without proper containment, the Giant Reed can quickly become invasive and outcompete other vegetation in the landscape.
Alternative Giants for the Landscape
While Arundo donax holds the height record, several other impressive species offer substantial size without its extreme growth habit.
Giant Miscanthus
Miscanthus giganteus, or Giant Miscanthus, is a popular alternative that typically reaches heights of 10 to 13 feet. This sterile hybrid is valued for its non-invasive nature and superior cold tolerance, often surviving in colder climates down to USDA Zone 4. Its thick, upright stems provide a dense screen, remaining attractive and architectural throughout the winter months.
Pampas Grass
Cortaderia selloana, commonly called Pampas Grass, grows to a height of 10 to 12 feet when its plumes are included. Pampas Grass is instantly recognizable by its huge, feathery plumes that range from silvery-white to pale pink, creating a dramatic visual impact. However, its evergreen foliage has sharply serrated edges that require cautious handling.
Ravenna Grass
For gardeners in colder regions seeking a similar look, Saccharum ravennae, or Ravenna Grass, is an excellent choice that offers comparable height. This hardy alternative can reach 8 to 12 feet, producing purplish-bronze plumes that fade to silver-gray in the fall. Ravenna Grass is significantly more cold-tolerant than Pampas Grass, thriving in zones as low as USDA Zone 5.