Giant Rhubarb: A Spectacular Architectural Plant
Gunnera manicata, commonly known as “giant rhubarb,” is one of the largest and most eye-catching herbaceous plants you can grow in your garden. It’s a member of the Gunneraceae family and is native to South America.
Appearance and Size
Giant rhubarb can grow up to 8 feet tall and 15 feet wide, making it a truly impressive specimen. Its massive, deeply lobed leaves resemble those of rhubarb, but they are much larger and can measure up to 6 feet across.
Growing Conditions
Giant rhubarb prefers moist, boggy soil and can tolerate full sun, partial shade, or dappled shade. It’s hardy to USDA hardiness zones 7-10.
A Note on Hybrids
A study by the Royal Horticultural Society revealed that many plants previously identified as Gunnera manicata are actually a hybrid of Gunnera manicata and the invasive Gunnera tinctoria. This hybrid has been named Gunnera × cryptica.
Invasive Potential
Gunnera × cryptica is considered invasive in some areas and has been banned from sale in certain countries. Gardeners with existing giant rhubarb plants should take steps to prevent them from spreading beyond their gardens.
Smaller, Non-Invasive Gunneras
Smaller gunnera species, such as Gunnera magellanica and Gunnera perpensa, are not invasive and are still legal to grow in most areas. These species are more compact and can be grown in smaller gardens.
Removal and Control
If you need to remove giant rhubarb from your garden, the best method is to cut it back completely and then dig it out. To prevent it from spreading, you can also cut off the flowerheads in summer before they produce seeds.
Similar Plants
If you’re looking for a plant with a similar effect to giant rhubarb but without the invasive potential, consider Rheum palmatum or Crambe cordifolia. These plants are non-invasive and offer bold, architectural foliage.
Wildlife Value and Toxicity
Giant rhubarb has no known value to wildlife in the UK. It is also non-toxic to humans and animals, including birds, cats, dogs, horses, and livestock.
Additional Tips
- Giant rhubarb is a fast-growing plant, so be prepared to give it plenty of space to spread.
- Water giant rhubarb deeply and regularly, especially during hot, dry weather.
- Fertilize giant rhubarb monthly during the growing season with a balanced fertilizer.
- Giant rhubarb can be propagated by division in spring or autumn.
