Thistles

“Andy, can you cut that plant on the drive down! It’s in the way and spiking me when I put Dusty in the car!” “Err, well, maybe I can cut it back a bit.. It’s the only spear thistle we have in the garden..” “Hmm..” is the response.

Why do I care about this thistle? Apart from it being architecturally impressive, standing at over 2m tall. Having beautiful purple inflorescences emerging from lovely grey-green prickle covered bulbs below (called involucres) and wonderfully fluffy thistle down seed heads (called pappus) that are highly valued by birds for their nests, and the attached seed for goldfinches to eat; being one of the best resources for pollinating insects and vital as the primary food source for the caterpillars of the painted lady butterfly that is 66% in decline since 2010. No reason at all really..

I do understand that most thistles aren’t particularly user friendly. But like most of us, once you get to know them they reveal themselves to be little softies, just don’t try to hug them, they really don’t like that!

Interestingly the spear thistle is a monocarpic perennial, this would seem to be an oxymoron as to be monocarpic, a plant flowers, produces seeds, and then dies, all within a single reproductive cycle. So it’s an annual right? Well no, many plants carry out their life cycle over two years as a biennial, in the same way that foxglove or mullein do, or as veg growers will know, a great many of the vegetables we eat are grown and harvested before they ‘bolt’ or produce a flower spike in the second and final year. 

Spear thistle Cirsium vulgare and the other thistles mentioned here are among less common company as plants that can live vegetatively for more than a year before flowering and ending their lifecycle. Actually the spear thistle does generally behave as a biennial, but it has a neat ability, if it has had a bad year and has not reached a sufficient size or has had poor environmental conditions, damage etc, it can delay flowering for another year. 

Probably the best known monocarpic perennials are some of the bamboo species that once they flower and seed, they die. Not only that, All bamboo’s of the same genetic makeup flower, seed and die at the same time, regardless of when they were planted or where in the world they live! And it can, in some cases, take over a 100 years. I’m drifting off subject..

Back to thistles, In a 2014 study to find which flowers are the best source of nectar. The AgriLand project, funded by the UK Insect Pollinators Initiative found that Marsh Thistle Cirsium palustre was the top plant for producing nectar per unit cover per year (kg of sugar/ha/year) and spear thistle was the 6th. To put that in context, there are 3842 plants in the wild. As an aside - only 1692 of those are native to the British Isles. Not just that, a staggering quote from the report states that: ‘The plant species that contribute the most at a national scale were White clover, Marsh thistle and Heather, which together contribute almost 50% of the national nectar provision.’

Well, WOW and yay to thistles!! 

I have used up my wordcount really but I am not going to go without mentioning a super cool thistle that I have hopefully propagated successfully from the wild (that is to say, the verge of a main road not too far from here). It’s in its first year of growth, so will flower next year hopefully. The woolly thistle Cirsium eriophorum, is an impressive one. Not quite as tall as the spear thistle but it has fantastic flower heads the size of a fist with downy webs on its spiky involucre and when it’s producing seed has a terrific amount of down. It grows on chalk usually so my garden may not be it’s favoured site, but it’s doing ok so far..

Photo by Carl Tronders