Gunnera manicata, often known as Giant Rhubarb or Dinosaur Food, is a striking perennial plant. Native to southern Brazil and Colombia, this herbaceous giant can grow up to 10 feet tall and 14 feet wide, creating a dramatic focal point in any landscape with its massive, puckered leaves that can reach 6 to 8 feet across. Its imposing presence and prehistoric look have made it a sought-after specimen for gardeners. Successful cultivation depends on understanding its specific environmental requirements, particularly its hardiness zone, to ensure it thrives.
Gunnera Manicata Hardiness Zones
Gunnera manicata is winter hardy in USDA Hardiness Zones 7 through 10, though it can survive in Zone 6 with substantial protection. The USDA Plant Hardiness Zone Map categorizes regions by their average annual extreme minimum winter temperature, guiding which perennial plants survive winter. Each zone represents a 10-degree Fahrenheit difference, with subzones (a and b) refining increments by 5 degrees Fahrenheit.
The plant’s cold tolerance dictates its zone limitations, as it is sensitive to prolonged freezing temperatures. While Gunnera manicata can endure temperatures as low as -12°C (10.4°F), its crown and rhizomes are vulnerable to deep or extended freezes, which can lead to damage or plant loss. In Zone 6, winter survival requires significant protective measures. Local microclimates can also influence a Gunnera’s success, potentially allowing it to thrive slightly outside its typical zone if conditions are favorable.
Ideal Growing Conditions for Gunnera Manicata
Beyond temperature, Gunnera manicata requires specific environmental conditions for vigorous growth. The plant prefers full sun to partial shade. In hotter climates, providing afternoon shade prevents leaf scorching.
The soil should be consistently moist, rich in organic matter, and well-draining. Good drainage is necessary to prevent root rot from waterlogging. Gunnera manicata tolerates various soil pH levels. It demands abundant, consistent watering, making it well-suited for boggy areas, pond margins, or beside water features.
Given its massive size, ample space is important for its root system and leaves to spread without overcrowding. Due to its rapid growth, Gunnera manicata benefits from regular feeding. Incorporating compost or well-rotted manure improves fertility, and a balanced, slow-release fertilizer applied in spring supports its development.
Winter Protection Strategies
Protecting Gunnera manicata during winter is important, particularly in colder zones like USDA Zone 6 or 7. The goal of winter protection is to shield the plant’s crown and rhizomes from freezing temperatures. These measures help ensure the plant survives the dormant period and returns in spring.
An effective method involves mulching the crown with a thick layer of organic material after the first hard frost. This can include the plant’s own dead leaves, straw, or other dry organic matter, acting as an insulating blanket. Gardeners often cut back dead foliage in autumn and pile it over the plant’s crown. Covering the mound with burlap or frost cloth provides extra insulation and helps keep the mulch dry.
Good drainage around the plant remains important to prevent waterlogging, which can lead to rot if the ground freezes. Winter protection should be applied in late autumn after the first frosts and removed in early spring once the threat of severe freezes has passed.
Common Growing Challenges
Even with careful cultivation, Gunnera manicata can face challenges. One common issue is leaf scorch or browning, which indicates too much direct sun exposure in hot climates, insufficient water, or low humidity. Providing afternoon shade and ensuring consistent moisture can help mitigate this.
Stunted growth can occur if the plant is not receiving adequate water, is planted in poor soil, or is outside its ideal hardiness zone without proper protection. The plant is robust, but it can occasionally be affected by pests such as slugs and snails. Root rot can also be a problem if the soil has poor drainage. While leaves naturally die back in winter, damage to the crown or complete winter dieback is a sign of insufficient protection in colder zones.