Frost on Gunnera

I took this photo in November last year at the Cambridge Botanic Garden.

Each year the gardeners at the Cambridge Botanic Garden stack Gunnera leaves in stooks like this.

They are not exactly stooks, because that word is specific to sheaves of grain stood on end in a field to dry out. Not that farmers put stooks out any more, probably not since before the Second World War.

But I am going to play fast and loose with the word and call these Gunnera stooks.

I mentioned to a friend in the Cambridge Botanic Garden recently that unlike previous years the Gunnera had not turned purple in the cold weather. We speculated it might be a function of when exactly the frost strikes – while the plant is full of sap, or when it has dried out.

The Royal Horticultural Society website entry for Gunnera it says “Frost can damage the crown of the plant.” So I guess a late frost could nip the crowns.

Now here are two more photos, the first taken on the 12th January this year and the second on the 18th January. Can you see the frost in the second photo? And the colour.

Gunnera In High Season

Gunnera amazes me. It puts so much effort into growing so big each year. I wonder whether I can encourage the Botanic Garden to put a plastic greenhouse over one plant for just one year, and not cut the leaves and ‘stook’ them – but leave it be so we can see what is happening over winter.

Gunnera manicata and Gunnera tinctoria

Gunnera manicata or Gunnera tinctoria, that is the question. Telling the two apart is not that easy.

I found a website – Lizzie harper: Natural history illustration for books, magazines & packaging – and an article she has on Telling Gunnera species apart. She very considerately points to another website, about which she says “For a really good article on comparing these amazing invasive plant species, please look at La Palmeraie. It was really useful when researching my illustrations.”

I looked at the illustrations and the photographs, and I am still not 100% sure which plant it is at the Botanic Garden.

If it is G. Tinctoria then according to an article last December in the Guardian newspaper, it has been banned from sale in the EU since 2017.

Moreover, all Gunnera are under suspicion because

” a study by the Royal Horticultural Society, which involved molecular and morphological analyses, as well as a historical investigation, has revealed that G manicata appears to have been lost from cultivation not long after it was introduced. In its place, the researchers found a hybrid between G manicata and G tinctoria, which has been named Gunnera × cryptica that is similarly invasive to G tinctoria and will now be banned.”

So is the plant at the Botanic Garden a relic of the no-longer existing Gunnera Manicata? Or is it Gunnera Tinctoria, or is it Gunnera × cryptica?

Update: It’s Gunnera Manicata

This is from a signboard in the Garden

What’s under the tents?
If you visit this part of the Garden in summer you will see the enormous leaves of the Giant Rhubarb (Gunnera manicata), which isn’t actually a rhubarb, but in its own plant family. The leathery, spiky leaves can grow to well over 1.5m in diameter. The plant has tiny red flowers which grow on thick, club-like, 50cm-long spikes.

Just like Ginger, Iris and Bamboo, the Giant Rhubarb grows from rhizomes – thick underground stems from which roots and shoots emerge.
Propagating the plant is as simple as cutting a chunk from an existing rhizome and burying it in damp, rich soil.
Over winter, the large buds from which the next year’s leaves will grow can be damaged by heavy frosts. In late autumn, our horticulturalists detach the leaves and cut the stems into shorter lengths, then use them to build wigwams to protect the buds from low temperatures.