Sleeping giants (and a little one) awaken
Gunnera manicata. Also known as the ‘Giant Rhubarb’, it is a colossus.
I first came upon the Giant Rhubarb in 2015 in the grounds of Winterbourne House, which is now part of the University of Birmingham Botanical Gardens, UK. Ah … Winterbourne House! The gardens …! The gardens were designed by the then lady of the house, Margaret Nettlefold after the homestead was built in 1903. What an inspiration! I must go back there this year … Forgive me, I digress.
In the gardens, I was awe-struck by the huge size of the Gunnera manicata leaves and the sheer scale of the plant in general. Standing amongst the leaves in the setting within which the plants grew was almost a surreal ‘other world’ experience. I felt as if I’d been transported back to the dinosaur age.
Prior to that day, I had no idea that such a plant existed. I just had to grow it!
But where? How?
A Gunnera manicata at Winterbourne House, Birmingham, UK. This photo doesn’t really do justice to the sheer size that the plant can attain. I don’t seem to have snapped the full-sized specimens within the grounds. Probably too awe-struck! : (
Please Google ‘Gunnera manicata’. You’ll see what I mean.
Gunnera manicata is a robust herbaceous, clump-forming perennial that can grow to a height of over 300 cm and a spread of 420 cm! The plants grow to their largest proportions when located in close proximity to open water. However, they can be grown successfully in drier soils as their roots penetrate to depths of over one metre. In dry conditions, regular, even daily watering, may be necessary.
Gunnera manicata is native to south-eastern Brazil. Yet more names include ‘Giant Brazilian Rhubarb’, ‘Chilean Rhubarb and ‘Prickly Rhubarb’. It is the largest of the 40 species in the genus Gunnera. The species is distributed across much of the southern hemisphere from South America and the Antarctic Islands, through South Africa and Madagascar to New Zealand. The smallest species, Gunnera monoica, is a New Zealand native with leaves only 3 cm wide.
Gunnera manicata has lobed, rounded, dark-green, rough-textured leaves, a staggering 100-300 cm in width, borne on tough spiny stems that arise from a stout crown. In summer, it produces tiny red-brown flowers borne in erect panicles to 100 cm in height, followed by orange fruit bearing seeds in the autumn. In jungle habitats the leaves can form vast canopies, providing shelter for man and wildlife. In Chile, the stems of the somewhat smaller Gunnera tinctora, also (rather confusingly) called Chilean Rhubarb, are used in cooking.
Gunnera manicata are striking, imposing architectural plants. However, the sheer size of the plant and its deep root system mean that Gunnera manicata is not suitable for long term container growing or small gardens.
Note! Gunnera manicata is listed on Schedule 3 of the EU (Birds and Natural Habitats) Regulations 2011 in the Republic of Ireland as and invasive non-native species. The Royal Horticultural Society (RHS) advice to growers is they care is taken in managing the growth of the plant and with the disposal of unwanted material. While the sale and growing of Gunnera manicata is not prohibited in Northern Ireland, the RHS does encourage gardeners thereto grow plants that are not listed on Schedule 3.
As it happens, I’ve discovered that Gunnera manicata or Giant Rhubarb isn’t really a rhubarb at all - Giant, Brazilian, Chilean, Prickly or otherwise!
So, will the ‘real’ rhubarb please stand up?
The ‘real’ culinary rhubarb is Rheum x hybridum, a hardy rhizomatous perennial which generally grow to a height of up to 90cm. There is a biggie about though, rhubarb Rheum x hybridum 'Victoria' which can reach a height of 250 cm and a spread of 150 cm after 2-5 years. Not quite Gunnera manicata, but pretty impressive nonetheless.
2019: One of my large rhubarb Rheum x hybridum plants, not at its best. It needed a lot of watering during dry spells in early summer. The leaves show some snail and slug damage. I won that battle in the end! The stalks were excellent.
As you will see, the leaves of Gunnera manicata and Rheum x hybridum are similar in shape. But that’s as far as it goes.
Like Gunnera manicata, the leaves of the ‘real’ rhubarb Rheum x hybridum are dark green too, but smoother, and significantly smaller, though, depending on the variety, they may grow to relatively large for a vegetable, average 30-45 cm in width. The stalks are not spiny.
Rheum x hybridum is a member of the Rheum genus of plants, but is of unknown origin. We know that rhubarb or ‘The Great Yellow’ root has been used in China for medicinal purposes for thousands of years. While Dioscurides documented (50-70 AD) a medicinal root brought to Greece from beyond the Bosphorus that may have been rhubarb, the commercial importation of rhubarb root into Europe did not become securely established until Islamic times. Rhubarb appears in medieval Arabic prescriptions.
Commercial trade via the Silk Route in Islamic times brought rhubarb root to parts of Europe in the 14th century through the ports of Aleppo and Smyrna. During this time, it became known as "Turkish rhubarb". Later, the same vegetable also came to Europe via Russia, and became known as ‘Russian Rhubarb’.
The high cost of transportation of rhubarb to medieval Europe and increasing demand from apothecaries resulted in efforts to cultivate the vegetable on European soil, in countries including England and the Netherlands. Rhubarb cultivation was introduced to Scotland by the traveller Bruce of Kinnear in the 18th century. The culinary rhubarb that is grown today is believed to be a hybrid of other Rheum species grown during these early times.
It is believed that Rheum x hybridum was first grown in the United States in the 1820s by the botanist, John Bartram, who planted seeds he received from Peter Collinson, a member of the Royal Society.
Today, Rheum x hybridum is grown mainly for its edible fleshy green, pink and / or reddish-coloured long stalks, that are used is deserts, preserves and beverages in countries where it is cultivated, including the UK, Europe and North America. At some point in the 18th century, rhubarb came into culinary use in parts of Europe, galvanised by the increasing affordability of sugar, a key sweetening agent. Rhubarb Crumble, often served with custard, is a popular dessert in the UK to this day. On the Indian subcontinent, the stalks are used in pickles, curries and other savoury dishes.
Rhubarb has a tart, tangy taste, and is low calorie, high fibre, and high in vitamin K1. It also contains some protein, calcium, potassium, vitamin C and folate.
The ‘stalks’ or ‘stems’ of the garden rhubarb are actually modified leaf petioles. The leaves themselves are dark green, smooth, and depending on the variety and conditions of culture, may grow to a width of over 30 cm. Nothing near Gunnera, but still pretty giant, as far as garden vegetable leaves go in temperate climes. The large Taino or Colocasia leaves grown in the tropics comes to mind.
It surprised me to learn recently that mature leaves of the rhubarb plant contain high levels of oxalic acid, which is potentially harmful to humans. For this reason, only the trimmed stalks are packaged for sale for human consumption in the UK.
Culinary rhubarb likes an open sunny site and moist but freely draining soil. Unlike the Giant Rhubarb, water-logging is a no no for Rheum, particularly in winter. The crown will rot. I try to keep the area around the plant weed free, and mulch with organic matter in spring to support growth and retain moisture. Flowering (pannicles of red flowers) is a natural part of the plant’s cycle but is an unwanted event for growers if the plant is being cultivated for culinary purposes, as it affects the quality and yields of the stalks. Some cultivars are more prone to ‘bolt’ to flowering than others. I haven’t had the ‘problem’ yet, but would immediately cut off any emerging flowers to preserve the crop. Slug and snails can be a problem. They devour young shoots and, if growth proceeds, whole leave surfaces.
I’m try to be proactive when it comes on to slug and snail control and rhubarb. This is because I grow rhubarb for ornamental as well as edible purposes. Two of my plants are mixed in with ornamental flowering plants. My eyes cannot abide large hole-ridden rhubarb leaves in the flower border!
Culinary rhubarb normally crops for a long period from spring through summer. The harvesting period varies with cultivar. Early season cultivars can be harvested from March or April onwards. Maincrop cultivars from late April or May onwards. For all cultivars, cropping can continue throughout the summer. A relatively recent introduction to the market (which I don’t have) is an autumn cropping rhubarb called ‘Livingstone’. If you’re impatient and can wait for the spring, you can you can ‘force’ the plant to produce edible stems 2-3 weeks earlier than normal by excluding light from the crowns from December onwards. I’ve never tried this. I’m can wait.
In autumn and winter, the vegetative growth dies right back. I clear away dead leaves to expose the crown to cold winter weather and frosts. Apparently, Rheum x hybridum plants need 6-9 weeks of cold weather (below 3 degrees centigrade) to crop properly when growth resumes in late winter and early spring.
It’s quite the opposite for Gunnera manicata. The leaves die pack in late autumn / winter too BUT I pile the dead leaves up around the crown to protect it from cold drying winds and frosts. The crown may die otherwise.
Today, I’m the proud owner of a Gunnera manicata plant! I worked out the ‘how’ and the ‘where’, and I’ve had it for three years now (it languished for one year in a pot before I planted it in the ground). It is growing from strength to strength but has not yet reached the jaw-dropping size of the specimens that I first saw at Winterbourne House. I cannot for the life of me find a picture of it in full leaf but I’ll make sure I take lots this year. In the meantime, I can show you photos of the leaf- covered and exposed crown though, taken this winter.
Top: The crown of my Gunnera covered with now rotting leaves for the winter. Bottom: New Gunnera leaves emerging from the crown on 27 February 2020.
Back to Rheum x hybridum now, my large, well-established rhubarb plants of unknown variety are waking up and forming leaves nicely …
01 March 2020: Large Rheum x hybridum leafing out now!
And here’s a little Rheum that’s awoken very early indeed …
02 March 2020: My small culinary rhubarb Rheum plant (is it some sort of dwarf?) has taken off early!
This culinary rhubarb (above) seems to be a not very vigorous ‘dwarf’ one that does not attain the vast proportions of the other cultivars that I have. It started life with me in a pot for one year, but has been in the open ground for nearly three years.
Culinary rhubarb can be grown in pots, best at least 50 cm wide and deep, in moist but well -drained compost. I do think that they are happier in open ground though, and certainly require less watering and feeding!
My small plant produces decent enough stalks for its size. I’m not sure whether it has become stunted as a result of the way I’ve grown it, or whether it is naturally ‘small’. Unfortunately I have no idea what the name of the cultivar is or where I bought it. I’ll keep an eye on it as it develops. Whatever the case, it has certainly got out of the starting block early!
I’m just thrilled to be a grower of ‘real’ culinary rhubarb varieties, as well as the ‘other’ Giant Rhubarb with gargantuan leaves that isn’t really a rhubarb at all.
My once sleeping rhubarbs are all awakening from their winter sleep now. Hoorah!
