If you’re obsessed with foliage, you’ve probably always longed to grow your own Gunnera manicata (GUN-ner-ah man-ih-KAY-tah), commonly called giant rhubarb. The gigantic, often heart-shaped, lobed, toothed leaves are stunning. While you’re more likely to see the colossal perennial on a trip to South America, depending where you live in Canada, you’ll spot the plant in places such as Vancouver and even Halifax. Gunnera is rated at Zone 8, but it can be nurtured in Zone 7 and even Zone 6.
Of the 45 or so summer-flowering species in the genus, there are drastic differences in leaf size. Gunnera manicata, native to the southeastern Brazil, is perhaps the largest species, with leaves typically five to six feet wide. Small species such as G. magellanica, sport leaves two to three inches wide on stalks three to six inches long. You’ll definitely need to assess space requirements carefully before taking one of the large varieties. The biggies do make gorgeous architectural plants for the edge of a pond or stream, or a bog garden, while smaller ones are interesting additions to a rock garden.
## 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 (see below); all varieties are unsuitable for high heat and humid climates.
* Gunnera manicata demands a virtually unlimited water supply in 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’t 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 large plastic container, such as a tub, and another 20 inches of straw (fresh wood chips or sawdust may work even better). Come late March or early April, protection can be removed (save the straw for mulch).
* 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.