A biennial which spreads by seed carried in the centre of spherical hairy parachutes during the autumn when they ripen, though most separate just a few feet from the parent and the seeds are carried on foot or are excreted after consumption in fodder. Most germinate in the autumn or the following spring when conditions are suitable, but they can remain dormant for up to three years in the soil. The plant grows at first as a rosette close to the ground with a tap-root and can survive mowing, becoming a monocarpic perennial if the flower spike is prevented from forming.

The dark green leaves have spines around the edges and on the surface, and are lighter underneath due to a dense covering of fine hairs. They are deeply lobed with a long spine at the apex of each lobe. The base of the leaf extends along the lower surface as a supporting wing.
In the late spring of the second year, it 'bolts' producing winged multi-stems which have spines up their length and can reach 1.5 metres in height. These produce many compound flowers with tufts of purple petals protruding from spheres of spined bracts.
In the film Braveheart a young girl picks a thistle flower and gives it to the young William Wallace, which is as believable as the accuracy of the history portrayed, unless she had hands of steel. The flowerhead can be harvested and when stripped of the spines and pappus, the bases can be treated like globe artichokes, eaten lightly steamed or raw.

After fertilization the seeds mature and the petals loose their colour. As the flowerhead dries up it splits open to release the pappus with a seed at their centres. The dried stems can remain for a few years if they are not disturbed, all the while releasing seeds.

The rosettes can be dug up and providing the crown is removed the tap-root will not regrow. Any plant which reaches the mature stage should be removed before the flowers lose their colour.
Selective weedkillers such as MCPA, 2,4-D and dicamba, are best used at the early rosette stage. Glyphosate can be used as a spot weeder.
Spear Thistle is an Injurious Weed and is specified in the Weeds Act 1959. It is therefore an offence to allow it to spread, though in practice this is not enforced. Indeed the Roads Authority is one of the major offenders by allowing Thistles to grow on road verges and shower the countryside with seed as they are wafted by passing traffic.