Gunnera manicata GIANT RHUBARB (10 seeds)

Giant Rhubarb, also known as Brazilian Gunnera, Chilean Rhubarb or Gunnera manicata in Latin, is a majestic perennial plant native to South America, specifically Brazil and Colombia. It belongs to the Gunneraceae family. This gigantic and impressive plant can measure over 3 meters in height and thrives in cool, moist soils in semi-shaded locations.

Its red flowering occurs from August through October, appearing in the form of spikes that rise above the plant's foliage. The individual flowers are small, generally measuring 3 millimeters in diameter, and grow in conical, branched panicles. They eventually produce spherical red-green fruits containing the seeds.

Brazilian Gunnera seeds are brown, round in shape, and measure an average of only one millimeter in diameter.

Its leaves are prickly and exceptionally wide, reaching up to 2 meters in diameter, forming a crown that spans several meters.
Note: Despite its common name, the foliage is unfortunately not edible.

- Uses:

Prestigious Horticulture and Water Gardens

The Brazilian Giant-Rhubarb is a flagship species of ornamental horticulture, famous for its monumental, prehistoric-style leaves.
It structures water gardens and wetland areas with majesty, offering an unparalleled visual impact.

Ecological Role and Bank Stabilization

A true refuge for biodiversity, this plant provides dense shelter for marshland wildlife.
Its powerful roots play a key role in stabilizing loose soil and actively contribute to the structure of riverbanks.

Biological Symbiosis and Nitrogen Fixation

Gunnera is of major scientific interest due to its symbiosis with cyanobacteria.
This unique nitrogen-fixing capacity allows it to grow vigorously, even in soils poor in essential nutrients.

- Germination and Sowing of Seeds:

• The most favorable period to sow Giant Rhubarb is in May.
• Soak the seeds in water for 12 hours before planting.
• Bury them 2 to 3 millimeters deep in small 5 cm pots using a well-draining horticultural potting mix.
• Water using a hand sprayer.
• Place the culture in a greenhouse in a warm, humid spot where the temperature is between 20 and 25°C.
• Germination is relatively slow; expect it to take between 4 to 8 weeks after sowing.

- Soil Type / Substrate:

The substrate must be cool, moist, and rich in organic matter. For pot cultivation, ensure the bottom is well-drained with a layer of clay pebbles. The soil should never be too chalky (alkaline) but rather slightly acidic.

- Exposure / Light:

It requires partial light to thrive. It prefers shaded areas while benefiting from indirect light for optimal development.

- Temperatures / Hardiness:

Once the plant reaches 3 years of age, despite its Brazilian and South American origins, it can withstand temperatures as low as -20°C if given some protection in winter. The optimal temperature for growth is 27°C. Its USDA hardiness zone is 7a.

- Watering / Irrigation:

It loves water and requires a humid, cool environment, though it should not have "wet feet" (standing water), which risks rotting the root system. Water thoroughly twice a day for the first 3 weeks after planting, then once a week during intense summer heatwaves.

- Multiplication / Reproduction:

Reproduction can be carried out in two ways: either by sowing seeds or by dividing the mother plant in spring or late autumn using the same substrate.

- Pests / Diseases:

It is rarely affected by diseases or the usual garden pests. Occasionally, it may face attacks from mollusks such as snails or slugs.

This article was written by Julien on 07/14/2026.