Giant rhubarb (Gunnera manicata), often referred to simply as Gunnera, is a truly impressive perennial known for its massive leaves and prehistoric appearance. Native to the cloud forests of Brazil, this plant can create a striking focal point in gardens due to its enormous size and dramatic presence. Despite its name, it is not related to the edible rhubarb commonly used in pies and desserts. Giant rhubarb thrives in moist environments and is perfect for adding a bold, architectural element to water gardens, large borders, and naturalized areas. Here’s a detailed guide on how to grow and care for this remarkable plant.
Characteristics of Giant Rhubarb
Leaves
The most striking feature of giant rhubarb is its enormous leaves, which can reach up to 6 to 8 feet (1.8 to 2.4 meters) across. The leaves are deeply lobed, rough-textured, and have a coarse, leathery feel. They grow on thick, spiny stalks that can reach 6 to 10 feet (1.8 to 3 meters) in height, making the plant look like it belongs to a prehistoric era. The leaves are a vibrant green, creating a lush, tropical effect.
Flowers and Fruit
Giant rhubarb produces small, greenish-red flowers in dense, cone-shaped clusters on tall spikes that emerge from the center of the plant in late spring to early summer. The flowers are not particularly showy but add to the plant's exotic appeal. After flowering, the plant produces small, round, orange fruits that are primarily ornamental and not suitable for consumption.
Growth Habit
This plant has a clumping growth habit and spreads slowly over time through its thick, creeping rhizomes. Gunnera forms a bold and dramatic clump that can cover a large area, making it ideal for use as a statement plant in expansive garden spaces. Its fast growth rate allows it to quickly fill out a space and establish itself as a dominant feature in the landscape.
How to Grow and Care for Giant Rhubarb
Light Requirements
Giant rhubarb prefers partial shade to full sun. In cooler climates, it can tolerate full sun if provided with ample moisture. In hotter regions, it benefits from some afternoon shade to prevent the large leaves from scorching. Finding the right balance of light and shade is essential to keep the plant healthy and vibrant.
Soil
This plant thrives in rich, moist, and well-draining soil with a slightly acidic to neutral pH. Gunnera is particularly well-suited to boggy or waterlogged areas where many other plants would struggle. Incorporating plenty of organic matter, such as compost or well-rotted manure, into the planting area can help retain moisture and provide the nutrients needed for vigorous growth.
Watering
Gunnera is a water-loving plant and requires consistent moisture to thrive. It performs best in areas with a reliable water source, such as near a pond or stream, or in gardens with consistently moist soil. Regular watering is essential, especially during dry spells or hot weather, to keep the large leaves from wilting and to maintain healthy growth.
Fertilizing
Giant rhubarb benefits from regular feeding, especially during the growing season. Apply a balanced, slow-release fertilizer in early spring and again in mid-summer to promote robust growth and large foliage. Organic fertilizers, such as compost or fish emulsion, can also be used to enrich the soil and support the plant's nutritional needs.
Pruning
Pruning giant rhubarb is minimal but necessary for maintaining its appearance and health. Remove any dead or damaged leaves as needed to keep the plant looking tidy and to prevent the spread of disease. In late fall, after the first frost, cut back the dying leaves to the ground and cover the crown with a thick layer of mulch to protect it from winter cold.
Pest and Disease Management
Giant rhubarb is generally resistant to pests and diseases, but it can encounter a few common issues:
- Slugs and Snails: These pests may chew holes in the leaves, particularly in damp environments. Hand-picking or using barriers and traps can help control their populations.
- Crown Rot: This fungal disease can occur in overly wet or poorly drained soils. Ensuring proper drainage and avoiding waterlogged conditions can help prevent crown rot.
Creative Uses for Giant Rhubarb
Garden Design
- Water Gardens: Plant giant rhubarb near ponds, streams, or water features where its need for constant moisture can be met. Its dramatic foliage and size make it an ideal choice for creating a lush, tropical atmosphere in water gardens.
- Shade Gardens: In shade gardens, Gunnera can be used as a bold, structural plant that adds a sense of depth and dimension. Pair it with other moisture-loving plants like hostas, ferns, and astilbes for a rich, layered effect.
- Naturalized Areas: Giant rhubarb can be planted in naturalized areas where its size and spreading habit can be accommodated. It works well in large, informal gardens or wild areas where it can create a dramatic impact.
Erosion Control
Due to its extensive root system and large leaves, giant rhubarb can be effective for erosion control on slopes and along stream banks. The plant's roots help stabilize the soil, while its foliage provides ground cover that reduces the impact of heavy rain.
Wildlife Habitat
The dense foliage of giant rhubarb provides excellent shelter for wildlife. Birds and small mammals can find refuge under its large leaves, making it a valuable addition to wildlife-friendly gardens.
A Historical Anecdote: Giant Rhubarb's Prehistoric Appearance
Giant rhubarb has an appearance so dramatic and ancient-looking that it's often referred to as a "dinosaur plant." This moniker is not just a playful nickname; Gunnera has existed since prehistoric times, and its colossal leaves and thick stems give it a primeval look that suggests it might have been a snack for dinosaurs millions of years ago. While we may not find dinosaurs wandering through our gardens today, the presence of giant rhubarb can transport us back to a time when plants ruled the earth with their sheer size and splendor.
With its impressive foliage, adaptability to moist environments, and ability to make a bold statement, giant rhubarb is a fascinating and rewarding plant for gardeners looking to add a touch of drama to their landscapes. By providing the right conditions and care, you can enjoy the majestic beauty and prehistoric charm of this unique perennial.