Some plants make us think of particular times of year, and when it comes to December, the poinsettia is a prime contender
We’ve used poinsettias for years to bring a touch of decadence to our festive displays, and this year we have the most stunning arrangement featuring three Christmas tree-shaped towers of them in The Glasshouse.
Our display is mainly of red and white, with the odd marbled pink in there too. But the colour comes not from flowers – they’re rather tiny green or yellow things in the centre – but from modified leaves called bracts.
You can find them in all sorts of colours - shades of red, pink, white, yellow and burgundy, some strong colour throughout, some marbled or speckled, or with coloured margins or splashes. (The Plant Centre here at RHS Garden Wisley has some that look like they’ve been flicked with paint!)
Poinsettias are also known as the Mexican flame leaf – they’re native to Mexico where they grow as straggly shrubs up to 3m (10ft) tall – so how did they come to be associated with Christmas? One legend is about a Mexican girl, called Pepita. She wanted to place a gift to the infant Jesus at the altar of her church, but was very poor and had nothing of value to offer. Her brother Pedro suggested she gathered a bouquet of weeds from the fields near her home. She arranged them as best she could, took them to the church and put them at the base of the crib. By Christmas morning they had turned brilliant red. They were, of course, poinsettias. Based on this legend, they are called Flowers of the Holy Night.
A word of warning, though. The Latin name of this plant is Euphorbia pulcherrima (‘pulcherrima’ means most beautiful) and all euphorbias contain a milky sap that can cause severe irritation if it comes into contact with the skin.
But what’s the origin of the name poinsettia? The species was given this common name poinsettia after the American Minister to Mexico, Joel Roberts Poinsett, who found the plant growing along a Mexican roadside in the 1820s and took cuttings back to his greenhouse in South Carolina. From there they were widely distributed. The Americans love them, and celebrate National Poinsettia Day on 12 December, the anniversary of the death of Joel Poinsett.
So, how do we get them to grow? In our displays we have 600 plants in each 'tree', grown from rooted cuttings which we potted in early July and encouraged to grow by placing on heated benches.
Wanting to create bushy plants, we pinched them out in early August to three to five nodes. But the bit everyone always wants to know is how to get them to colour up. This is the critical part… to initiate flowering, and the associated bract colour, poinsettias need 12-14 hours of complete darkness daily for two months. Like other plants that flower at this time of year, they are known as short-day plants because shortening daylength is the cue for flowering to start.
Finally, poinsettias are brilliant if you keep them cosy and warm (think Mexico). That’s why they like The Glasshouse! So beware of drafts and dropping temperatures when you buy one to take home.
The only thing left is to decide on the size and colour….
Next time, read Olive’s blog on how the team in The Glasshouse put the display together.
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