How to Grow Gunnera Plants in your Garden

Gardener's HQ Guide to Growing Prickly Rhubarb and Giant Rhubarb

Members of the Gunnera genus are hardy perennials that can reach up to 1.8 metres in height, and are often wider.

They have very large leaves that are both lobed and toothed.

Though they bloom in summer and the start of autumn, it is the attractive combination of foliage and flowers that Gunnera plants are usually grown for.

The flowers grow to be cone shaped and may be red, yellow or green. A commonly grown member of the genus is Prickly Rhubarb.

Gunnera
Gunnera by saxifrage.

Gunnera Plant Growing and Care Guide

Common Names: Gunnera, Prickly Rhubarb, Giant Rhubarb.
Life Cycle: Hardy perennial.
Height: 100 inches (250 cm).
Native: Southern America.
Growing Region: Zones 6 to 9.

Flowers: Middle of summer to early autumn.
Flower Details: Red, yellow. Small. Cones. Massive.
Foliage: Herbaceous. Lobed. Toothed. Large leaves may reach over 9 feet (275 cm) in length. Succulent stalks.

Sow Outside: Cover seed. Following the last frost. Spacing 48 to 120 inches (120 to 300 cm).
Sow Inside: Germination time: two weeks to two months. Temperature: 60 to 70°F (16 to 21°C). Seven or eight weeks in advance. Transplant outdoors a few weeks after the last.

Requirements and care: Full sunlight or partial shade. Soil should be prepared beforehand so as to be deep. Boggy soil, Moist soil, rich soil. Regular watering during dry periods. Regular liquid feed. Leaves should be cut back to the ground in autumn. Then cover the crowns with a leaf mold. Propagate: by dividing in the spring.
Miscellaneous: Gunnera is considered to be an invasive species in many areas, especially parts of New Zealand.

How to Grow Prickly Rhubarb and other Gunnera Plants in the Garden

When growing prickly rhubarb and other Gunnera plant species outdoors from seed, sow just after the last frost. Lightly cover the prickly rhubarb seeds once sown.

They are very large plants so space the Gunnera plant at 1.2 to 2 m (4 to 7 feet) apart. The larger, Gigantic Gunnera species needs to be grown at least 3 metres (10 feet) apart.

Plants are able to grow in both sunny and partially shaded parts of the garden.

Due to their massive size it is important that Prickly rhubarb and similar plants have a very deep soil in which to grow. The soil should also be rich and moist.

If starting off indoors, sow Gunnera seeds about eight weeks in advance. The seeds should typically take from two to ten weeks to germinate at a temperature of 15 to 20 degrees centigrade (59 to 68°F).

Caring for Gunnera Plants

As Gunnera plants such as Prickly & Giant Rhubarb are very large plants, they require a lot of water and food. Water them frequently and supply regular feeds of liquid fertilizer.

Once they have finished flowering in the autumn, cut off their leaves. Then cover their crowns with a mulch of leaf mold.

If you require more plants then propagate plants in the spring by division.

Common Questions

How many members does the Gunnera genus have?

The Gunnera genus consists of about 40-50 species.

Do members of Gunnera make a good garden or landscaping plant?

Yes, Gunnera are often used for dramatic effect in gardens due to their large, prehistoric-looking leaves, making them excellent for waterside planting.

Which Gunnera species are most frequently grown by gardeners?

Gunnera manicata, also known as Giant Rhubarb, is a popular choice for its massive, architectural leaves.

Are members of the Gunnera plant genus fragrant?

Gunnera plants are not known for having fragrant flowers.

What is the perfect location to grow Gunnera?

Gunnera thrives in a location with full sun or partial shade and rich, moist soil. They're particularly suited to waterside locations.

Is Gunnera invasive in the USA, if so in which states?

Presently, Gunnera is not listed as an invasive plant in the USA.

How do I remove Gunnera plants from my garden?

To remove Gunnera, cut back the plant and dig out the root system. Dispose of plant material responsibly as it can spread from pieces of root.

Summary

The Gunnera genus, part of the Gunneraceae family, originates from the cool and damp regions of South America. Often known as Giant Rhubarb, these perennials are remarkable for their enormous, rhubarb-like leaves and spiky flower clusters.

Plant Gunnera in spring or fall, in a location with part shade to full sun and rich, deep, well-drained soil. They prefer a spot near water bodies as they need ample moisture to thrive. Protect the crown with the dead leaves during winter in colder climates.

I hope that you enjoyed this guide on how to grow Gunnera plants. You may also enjoy my gardening guides on how to grow Cornflower, Celeriac, Cyclamen plant, and Bulbinella plants.