If you have a large space that needs to be filled in your landscaping and want a conversation piece, then the Gunnera plant may be just what you need. Gunnera plants are tender perennials in zones 6 to 8 that resemble the rhubarb, but grow giant dark green leaves that can span 6 feet across. There are over 40 species of gunnera, and not all of them have the gigantic leaf size, so one should fit into your landscape needs.
Gunnera plants can be started from seeds, bulbs or purchased plants. Plant seeds or bulbs after the threat of frost has passed, but wait another month before planting the purchased trousers. The soil needs to be very humus-rich, loamy and well-draining. Work a good quantity of animal manure into the soil to increase the compost and humus level. Gunnera seeds should be planted 1 inch below the surface; bulbs about 6 inches. Remember, these plants are expansive and can be 10 to 12 feet wide, so leave 6 to 9 feet between plants. Gunneras are fast-growing, under the right conditions, and will fill in the space quickly.
Location, Watering and Feeding
Gunneras grow well in full sun, as long as the temperature range is between 23.9 to 29.4 degrees Celsius. They do thrive in partial sun or shade. If you live where there are periods of extreme high heat in the summer, it is advisable to plant your gunnera where it will be shaded during the heat of the day. Too hot of an environment will cause the leaves on a gunnera to turn brown on the edges. Always thirsty, gunneras need consistently moist soil and are often around a pond or near streams. If not planted by a natural water source, make sure you water your gunnera often so the soil never dries out. Continue to infuse the soil with well-rotted manure and a general liquid fertiliser every month throughout the growing season. Because of the gunnera's water needs and rapid growth, it needs more feeding.
The larger-leafed gunnera does not tolerate wind, particular dry wind, so plant in a protected area.
In the fall, after the gunnera has stopped flowering, or after the first frost, cut off the leaves to the crown. Be very careful doing this. The stem and leaves have small prickly hairs that will cut and jab you. Also, direct contact with the leaves, for some people, will them give an allergic reaction. Use the leaves to cover the crown for winter protection, or use a thick layer, over 12 inches, of mulch and straw. In the spring uncover and remove the leaves or mulch.