Lawn and Garden Shop
Garden Improvement Information Series
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Lawn and Garden Shop
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Gunnera is a genus of herbaceous flowering plants, some of these are gigantic. The genus Gunnera, was named after Johann Ernst Gunnerus (1718–1773), a Norwegian botanist.
The genus is the only member of the family Gunneraceae. The 40-50 species vary enormously in leaf size. Of the 45 or so summer-flowering species in the genus, there are drastic
differences in leaf size.
DESCRIPTION: These perennials are mainly grown for their beautiful foliage. Gunnera (commonly known as the Giant or Prickly Rhubarb)
isn't hardy in very cold climates; they are natives of South America, South Africa, Tasmania, Abyssinia, Java, New Zealand and Hawaii. The natives of South America eat the thick leafstalks of Gunnera manicata and
Gunnera chilensis either raw or cooked; they are known as Pangue. The Rhubarb plant used to make pies, tarts, etc. is Rheum rhabarbarum.
PROPAGATING GUNNERA MANICATA:
Propagation can done by dividing the rootball or by the method most commonly used which is by dividing rhizomes, tubers, corms or bulbs, including offsets.
Another propagation method used is by planting their tiny seeds. Tiny red-brown flowers are borne in erect panicles to 1m in height. followed by small red berry-like fruits.
Sow these seeds in gentle heat as soon as ripe, seed quickly loses viability.
Germination may be improved by maintaining very moist, but not wet, conditions and temperatures of 75-85 degrees Celcius. Germination should happen within two weeks.
Germination may be slow and erratic, so prick out individual seedlings as they become large enough to handle and transfer to pots or trays. Over-winter in a cool, frost-free shed or greenhouse and plant out in April or May.
Gunnera has roots that are host to microscopic blue-green algae, which convert atmospheric nitrogen into a soluble form of nitrogen that the plant can use for growth.
NOTE: In Nature, water is the main way that the Gunnera seeds spread and colonize other areas. Birds are secondary.
GROWING TIPS:
Gunnera species grow in deep, permanently moist, humus-rich soil in sun or partial shade.
Large varieties need shelter from cold, drying winds and winter protection; all varieties are
unsuitable for high heat and humid climates.
Gunnera manicata demands a virtually unlimited water supply in their growing season
that’s why it’s ideally planted along the edge of a stream or a pond). Plant it right after the
last frost in spring and add as much compost, well-rotted manure and slow-release fertilizer as
possible to the soil. Even after the plant has settled in, massive amounts of compost, manure and
fertilizer are needed.
Unprotected crowns can not survive temperatures below -8°C. The crowns of smaller varieties
should be protected with dry mulch. The leaves of larger varieties should be cut off after the
first hard frost.
Inverted, the leaves provide excellent coverage for the resting crowns. Another method to help
keep out moisture is to remove leaves after the frost, cover the crown with 20 inches of straw,
cover with a burlap tarp, or large plastic container, such as a tub, and than add another 20
inches of straw. Seasoned wood chips or sawdust will work even better. After all danger of a
hard freeze is gone, in late March or early April, protection can be removed. Then be sure to
mulch the Gunnera plant.
Sow seeds in containers as soon as they are ripe and keep them cool but frost-free through the winter.
Germination is slow. Large species can also be increased by taking cuttings of leafy, basal buds in
spring. Divide small species in spring.
Gunnera plants may be planted in large containers for their first few years, depending upon their
need for deeply cultivated, moist, fertile soil, in a sheltered location. Gunneras are
great for waterside planting and other moist places. The crowns of these plants should be protected
in the winter by mulching with dead leaves.
The larger Gunnera make gorgeous architectural plants for the edge of a pond or stream, a waterfalls setting, or a bog garden,
while smaller species make interesting additions to a rock garden.
Cyanobacterial Symbiosis:
In nature, all Gunnera plants form a symbiosis with a nitrogen-fixing cyanobacteria,
thought to be exclusively Nostoc punctiforme. The bacteria invade the plant via glands
found at the base of each leaf stalk[1] and initiate an intracellular symbiosis which
is thought to provide the plant with fixed nitrogen in return for fixed carbon for the
bacterium. This intracellular interaction is unique in higher plants and may provide
insights to allow the creation of novel symbioses between crop plants and cyanobacteria,
allowing growth in areas lacking fixed nitrogen in the soil.
Scientific classification:
Gunnera albocarpa
Gunnera arenaria
Gunnera densiflora
Gunnera dentata
Gunnera flavida
Gunnera hamiltonii
Gunnera magellanica
Gunnera magnifica
Gunnera manicata
Gunnera masafuerae
Gunnera monoica
Gunnera perpensa
Gunnera prorepens
Gunnera tinctoria
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This web site was first published November 08, 2003.
This page was last updated September 22, 2018.