Common Name: giant rhubarb
Type: Herbaceous perennial
Family: Gunneraceae
Native Range: Southern Brazil, Colombia
Zone: 7 to 10
Height: 6.00 to 10.00 feet
Spread: 8.00 to 14.00 feet
Bloom Time: June to July
Bloom Description: Reddish-green
Sun: Part shade
Water: Medium to wet
Maintenance: Medium
Suggested Use: Rain Garden
Flower: Showy
Fruit: Showy
Tolerate: Wet Soil
Culture
Winter hardy to USDA Zone 7 where it is best grown in fertile, humus-rich, consistently moist to boggy soils in part shade. Leaves often becomes stressed in full sun locations. Soils must never be allowed to dry out. Plants are intolerant of extreme heat of cold. They rarely succeed in hot or dry climates. Remove damaged or dead leaves as they appear. In the northern parts of this plant's growing range, plants should be sited in protected areas sheltered from drying winds and given a substantial dry winter mulch. North of USDA Zone 7, plants are not considered to be winter hardy. Bare roots should be lifted before the first fall frost for storage in cool areas (40 degrees F.) in a dry medium such as peat or vermiculite. Bare roots may be replanted outside in spring after last spring frost date. Plants may also be grown in containers that are moved inside to a cool, frost-free location such as an unheated garage where they will go dormant for winter. Apply minimal moisture to the soil every 10 days. Plants may be propagated by division or seed.
Noteworthy Characteristics
Gunnera manicata, commonly called giant rhubarb, is one of the largest herbaceous perennials on earth, typically growing in a rounded clump to as much as 10' tall and to 14' wide. It is native to southern Brazil and Columbia. Huge, puckered, toothed, palmately-lobed, prominently-veined leaves (to 6-8' across) with rounded to reniform (kidney-shaped) blades are borne on stiff, prickly, reddish-hairy stalks to 8' long. Leaves are peltate, tilting to the horizontal. These dinosaur-sized leaves give rise to the additional common name of dinosaur food for this plant. Tiny, reddish-green flowers in thick, club-like spikes (3-6' conical panicles) rise up from the crown in early summer. Flower spikes are often somewhat hidden by the foliage. Flowers give way to reddish-green fruits (tiny berry-like drupes). Although botanically unrelated to rhubarb, the coarsely-textured leaves of this gunnera are considered by some to be reminiscent of the leaves of rhubarb.
Genus name honors Johan Ernst Gunnerus (1718-1773), Norwegian bishop (at Trondheim) and botanist, the author of Flora Norvegica (1766-1772).
Specific epithet means with long sleeves.
Problems
No serious insect or disease problems. Watch for slugs and scale.
Uses
Primarily grown for its gigantic leaves, but the flower spikes are also attractive. Wet areas of the landscape. Water gardens. Pond peripheries. Bog gardens.