Eryngium pandanifolium, Giant Sea Holly, is one of the largest of the Eryngiums and is native to Argentina, Uruguay, Paraguay and southern Brazil where it tends to grow in damp ground and along riverbanks. A magnificent rosette-forming triffid of a thing with long sword-like silvery glaucous-green leaves, Eryngium pandanifolium establishes a dramatic architectural presence in the garden that simply can't be ignored. It is an exceptionally quick-growing plant and its attractive spiky-margined arching foliage - resembling a Puya - will, by mid-summer, have begun to send up its tall flowerspike that rapidly reaches up to 3m in height, the small tufty flowers slowly turning from pale green to pinkish-purple as the season develops. Because of this extraordinary height it is best situated in a sheltered but sunny position where it has some protection from the prevailing winds.

Hardy in those parts of the UK that enjoy a milder climate its geographic range can be significantly extended by wrapping its base in horticultural fleece during the worst of the winter weather. We grow it outside at our Surrey nursery and it has survived frost and snow for many years. It forms a large clump by creating offsets and at the end of each autumn when the flower-spike has begun to turn brown some of these offsets can be separated and kept in pots and placed in a glasshouse or on a windowsill as an insurance in case of a brutal winter. Given a good thick mulch it will sprout again in the spring.

A wonderful plant and always a talking point.