Eryngium (Sea Holly)

Cones of tiny florets surrounded by a ruff of spiky bracts, the whole thing in metallic steel-blue, above branching silvery-blue stems at 70 to 90cm. It reads as sculpture more than as a flower, which is exactly why it works next to soft rounded things.

The colour arrives in June and the central florets finish by August, but the bracts stay blue and hold their shape well into autumn, so the structural value runs far longer than the flowering. Dried, it keeps that metallic blue for years, and we use a good deal of it in the dried range here.

It is as drought-tolerant as any perennial we sell and it tolerates salt, so it is a genuine coastal plant. What it will not tolerate is wet feet in winter, which is what kills it in a heavy garden. It makes a long taproot early, so it hates being moved and does best sown where it is to grow, or planted out young. Expect two years before it looks like anything.

The bracts are genuinely sharp. Wear gloves to cut it.