RARELY a month goes past without this column mentioning architectural plants. These are statement plants selected for impact, those that offer something more than just colourful flowers.
They may boast bold foliage or eye-catching bark, and they are usually big, often maintaining their imposing statuesque shape even after their leaves or flowers have died back.
If I were to nominate a wildflower that fits this bill it would be the spear thistle, one of our most common, persistent and bodacious weeds.
Cirsium vulgare is a biennial that tends to appear on neglected ground and in arable fields. The seeds from which it reproduces are soft and cotton-like, dispersed on the wind. A majority of the thousands each flower produces are eaten by birds and small mammals, but where it does germinate, the plant will overwinter as a rosette.
The following year it develops into a tall (1m-plus), robust downy plant with leaves and stalks covered in sharp jags.
Between July and September, it produces sweet smelling purple flowers that are attractive to bees and then goldfinches after the seed sets in the autumn.
The thistle’s use in Scots heraldic tradition is thought to date back to long before King James II created the Order of the Thistle in the late 17th century, popularising the flower as a Scottish emblem.
The spear thistle – Feochadán colgach, as Gaeilge - despite being a native wildflower and important for biodiversity, is among a number of plants classed as ‘noxious weeds’.
Every year, Stormont’s Department of Agriculture, Environment and Rural Affairs (DAERA) reminds farmers and landowners of the need to control noxious weeds, which also include ragwort, creeping thistle, broad leafed docks, curled leafed docks and wild oats.
Given the department’s poor record in prosecuting farmers for polluting waterways or trashing areas of special scientific interest, you’ll not be surprised to learn that nobody has ever been brought to book under the Noxious Weeds (Northern Ireland) Order 1977.
But unless you’re going for the full rewild, it’s still advisable not to encourage Cirsium vulgare in your garden.
There are, however, some alternatives that will deliver a similar architectural impact without the jags.
Onopordum acanthium, the cotton or scotch thistle, is a taller, non-native biennial that’s deployed only by the most daring gardeners, as it requires plenty of space and some complementary context. Growing up to 3m, it is the ultimate in feature plants, with big lilac flowers sitting on stiff velvety stems.
Not strictly speaking a thistle, but similar in flower shape is Centaurea montana, sometimes known as perennial cornflower. Popular, as it’s unfussy and easily propagated from root cuttings, this flowers early in the summer and will withstand a chop to improve its appearance and encourage a second flush. It can cope with semi-shade or full sun and is drought tolerant.
The easiest to manage and most effective substitute is Echinops – or globe thistles. Bred from species that originally hail from around the Mediterranean, this member of the Aster family is too drought tolerant and not particularly fussy about soil quality, as long as it’s not damp. Grown from dormant rhizomes, they should be planted en-masse, in full sun to ensure erectness, ideally among grasses and other prairie plants
Echinops ritro, is a arguably the most common variety and has the RHS’s Award of Garden Merit. Echinops bannaticus ‘Taplow Blue’ is another good beginner’s plant, while the recommended variety if you don’t have too much space is Echinops ritro ‘Veitch’s Blue’.
