How to Plant and Grow Gunnera

One of the largest perennial plants on earth, gunnera is also known as giant rhubarb or dinosaur food. It can form a clump 10 feet tall and up to 14 feet wide. In late spring, corncob-like flower stalks 2 to 3 feet tall emerge near the roots that will turn into tiny berry-like (inedible) fruits. Gunnera is a tropical plant native to southern Brazil and Colombia. Consistently wet soil and a moderate climate are key to great gunnera growth.

Where to Plant Gunnera

 Select a location in partial shade where gunnera has ample space to grow and does not interfere with other plants, as its leaves create broad canopies. Also, keep it away from buildings and other structures.

The soil should be consistently moist but not soggy and can be slightly acidic, neutral, or alkaline.

Ideal places are near water gardens, rain gardens, ponds, or bogs where soil is always moist. Gunnera's bold presence makes it an excellent focal point in the garden. Pair it with plants that can stand up to it with their own eye-catching attributes.

How and When to Plant Gunnera

Plant gunnera in early spring after there is no more danger of frost. Dig a hole about twice the diameter of the root system and as deep as the nursery container. Backfill with original soil and tamp it down. Water well and continue to water plants regularly, especially if the soil is not naturally wet, to encourage a strong root system.

Even if the planting space is large, because of the enormous size of the plant, it is better to start with a single specimen and see how fast it fills the space before planting more.

Gunnera Care Tips

When the conditions for moist, humus-rich soil and shade are met, gunnera is easy to grow and spreads to form a lush clump.

Light

Gunnera is best planted in partial shade. However, it will tolerate full morning sun if it's protected from direct afternoon sun, and the soil is never allowed to dry out.

Soil and Water

While gunnera is adaptable to different kinds of soil and acidic, neutral, and alkaline pH, ample moisture is a must. If it is not planted where the soil is naturally moist at all times, be prepared to water it regularly in the absence of abundant rain. Especially young plants need frequent watering until their roots are at least 1 foot deep.

Temperature and Humidity

Gunnera does well in a warm, frost-free climate but does not tolerate hot or dry climates. If you grow it in Zone 7, select a location that is protected from cold, drying winter winds. Also, use the dead leaves to protect the crown from the winter cold (see Pruning). A 2-inch layer of hardwood mulch around the crown provides additional protection in colder climates.

Fertilizer

If grown in the right conditions, gunnera usually does not need a nutrient boost. If it seems to languish, apply a balanced slow-release fertilizer in the spring, following product label directions.

Pruning

Remove damaged or dead leaves as soon as they appear. In the fall, when the foliage has died back after the first frost, cut the leaves down to ground level and place them over the crown like mulch; remove them in the spring before new growth starts. This protects the crown from the winter cold.

Potting and Repotting Gunnera

Because gunnera is so large, growing it in a container can be challenging. If you live below Zone 7, growing it in a container allows you to move it inside to a frost-free location, such as an unheated garage or basement. The plant will go dormant during the winter. It should only be watered minimally during this time, about every 10 days.

Choose a container that is large and deep enough to accommodate the roots of the plant plus at least 6 to 12 inches for future growth. Use rich organic potting soil and keep in mind that potted plants need more frequent watering and fertilization than plants in the landscape.

Not repotting gunnera when it has outgrown its container lets you control its growth for a while. Nonetheless, every other year or so the plant will benefit from fresh soil.

Pests and Problems

Gunnera is rarely affected by serious pest or disease problems. Slugs and scale insects might feed on the plant.

How to Propagate Gunnera

Gunnera seeds are not commonly available from seed companies. The recommended method of propagation is from the roots yet this is not the typical division. As the plant is so large that digging it out and lifting it out of the ground is often not possible, you can just cut a portion of the crown in the early spring before new growth starts. Replant it at the same depth in a new location where it has ample room to grow and keep it evenly moist.

Types of Gunnera

Chilean Gunnera

Reaching 5 to 6 feet in height and width at maturity, Gunnera tinctoria is smaller than Gunnera manicata. Its leaves have spines. It is also a potentially invasive plant. Zone 7-9

Creeping Gunnera

Also known as devil’s strawberry, Gunnera magellanica grows only 8 inches tall and serves as a semi-evergreen groundcover. Zone 7-9

Gunnera Companion Plants

Hardy Hibiscus

With its vibrant, dinner plate-size blossoms and deep reddish-green to burgundy foliage, hardy hibiscus is a showstopper. It grows easily in moist to wet soils with exposure to lots of sunlight. Zone 4-9

Canna

Canna, which—like gunnera—boasts a tropical appearance and bold leaves, blooms for more than six weeks beginning in midsummer. In their native habitats, cannas are often seen growing close to and even in the water, which makes them ideal candidates for landscaping around a pond. Zone 7-10

Ligularia

With giant, coarse-textured leaves, perennial ligularia makes a foliage-heavy addition to shade gardens. Plant it in moisture-retentive soil; you may even consider placing it alongside water gardens. Zone 4-9