Silver

Eryngium bourgatii - stellar

Onopordum acanthium - three thistley ghosts

My (male) neighbours at the allotment find space to grow some striking, spikey ornamentals, pictured here in mid-June.

Eryngium is a clump-forming perennial about 50cm high, so this view of its stellar bracts can be made a point of interest. If you plant it by a path, feel confident your guests will have their gardening trousers on. Hardy, so long as it's on free-draining soil. 

The Scotch thistle - a native plant and un-cultivared - being up to 3m tall, is often placed at the back of a traditional herbaceous border. Here it is displayed in all its glory, making full use of the toning mortar and contrasting brick behind it. It's a biennial that successfully self-seeds (such fun for weeding) and does well against this south-ish facing wall on unimproved soil