Gunnera is a group of herbaceous perennial plants primarily known for their enormous leaves. The largest and most well-known Gunnera is G. manicata, commonly called giant rhubarb or dinosaur food, which has leaves that can reach over 6 feet in width, according to an article published by Fine Gardening. On the other hand, G. magellanica has leaves that are only a few inches across. Caring for Gunnera plants requires only basic culture.
Gunnera plants are native to South America and prefer warm, humid weather. They grow best outdoors in U.S. Department of Agriculture (USDA) hardiness growing zones 7 through 10.
Some Gunnera plants can be started by seed, although they take a long time to germinate. Others start from bulbs, and still others are best purchased as young plants. The larger the leaves, the slower these plants tend to grow. Wait a month until the last frost has passed before planting. Plant plants as deep as the root ball, and bulbs 6 inches below the surface. Seeds can be pressed an inch into the dirt. Remember to leave plenty of space between plants--at least 6 feet--if you are growing one of the giant varieties.
Soil and Water
Gunneras prefer loamy soil rich in nutrients. Amend your soil with hummus, leaf mold or other organic material before planting. The soil should be very moist. These plants are often found growing along streams in Brazil, according to information published by Desert Tropicals, and thus should be kept moist at all times. Or plant your Gunnera near your own stream or pond.
Gunneras will grow in sun or partial shade, according to information published by Gardening Life. They thrive in high heat and humidity but need protection from cold, drying winds. The larger the variety, the more protection it needs, so plant it near a south-facing wall or fence if possible.
This plant requires massive amounts of nutrients, according to Gardening Life. Mulch it well with organic mulch and manure. Fertilize your Gunnera with a balanced (10-10-10), slow-release fertilizer in the spring according to the directions on the label for the size and age of your plant.