Thistle do nıcely!

Far from being just a prickly nuisance, thistles can be a spectacular asset to your garden, says Monty Don – and some are edible too

Thistles tend to be branded as spiky weeds thanks to their ability to reproduce themselves voraciously if allowed to seed. The ones that trouble gardeners most are the creeping thistle, Cirsium arvense, which has mauve flowers and vicious prickles and can spread fast; and the spear thistle, C. vulgare, which has large, deeply lobed leaves edged with spines, as well as spines on the stems. However, the seeds of the creeping thistle are an excellent food source for finches, and the foliage is important for the caterpillars of more than 20 types of butterfly.

Then there are the sowthistles, Sonchus asper and S. oleraceus, the leaves of which are high in vitamin C and can be used in salads.

Not all thistles are weeds, and there are plenty that look superb while being very manageable. Cirsium rivulare ‘Atropurpureum’ delights in damp or heavy soil. It grows to just over 1 metre tall, with plum-coloured flowers that first appear in May and continue throughout June. The leaves are hardly prickly at all, making it very border friendly. It is a shortlived perennial so is liable to suddenly disappear just when it is looking superb – usually after three years – and is sterile so will not produce seedlings, which means it is a good idea to lift it every couple of years and take root cuttings.

The globe thistle, Echinops ritro, is a tough herbaceous perennial, happiest in poor soil as long as it gets some sun, and although its leaves are horribly prickly, the blue pompom flower heads justify the occasional painful encounter. But it does need lifting and reducing every few years – keep the outside sections and discard the rest. Echinops bannaticus ‘Blue Globe’ is darker and E. bannaticus ‘Taplow Blue’ is a very good, intense blue.

Perhaps the most popular ‘thistle’ is not really a thistle at all, but a distant cousin of

the carrot – although it does have a powerful armoury of spikes and prickles. This is the giant sea holly, Eryngium giganteum, commonly known as ‘ Miss Wilmott’s Ghost’ after 19th- century gardener Ellen Wilmott, who used to secretly scatter its seed in other people’s gardens so they might enjoy it too. It is silver, tinged with blue. Eryngium ‘Silver Ghost’ is smaller and more silvery white. It is a short-lived perennial and, like all eryngiums, likes poor, very well- drained soil and full sun.

Cardoons ( Cynara cardunculus) start life in spring as a fountain of lovely glaucous cut leaves that make a superb backdrop for flowers but then grow enormous with their thistle flowers carried on a candelabra of stems as thick as your wrist. This means they need extensive propping up, but if you have the space they’re worth the trouble because they add real stature to any border. They are herbaceous, so disappear in winter, although the flower stems need a powerful shredder to convert to compost.

I’ve saved the biggest and best until last. The cotton thistle, Onopordum acanthium, is a magnificent plant on an epic scale. It has huge grey leaves coated with a milky down and fringed with wicked spikes, and boasts candelabras of flowering stems growing to at least 3 metres, with a spiny spread of around 1.5 metres. It is biennial and, like all thistles, seeds itself everywhere. Decades ago I planted five in my small London garden. An older, wiser friend said I was mad. Perhaps I was – but I’ve remained mad about these lovely thistles ever since.

Monty with his cardoons ( Cynara cardunculus)