Siberian iris

Arkansas blue star (Amsonia hubrichtii), also called threadleaf bluestar or Hubricht's bluestar, is a clump-forming native perennial from a tiny wild range in the Ouachita Mountains of Arkansas and Oklahoma that has become one of the most dependable foliage perennials in temperate gardens. It builds a soft, rounded, knee-to-waist-high mound of upright stems clothed in very fine, needle-like, thread-thin leaves, so the whole plant reads as a feathery green cloud through summer. In late spring the stem tips carry loose clusters of small, pale powder-blue, five-pointed star flowers, a quiet but pretty show that draws butterflies and other pollinators. Its headline act comes in autumn, when the fine foliage turns a clear golden-amber that lights up the border and earned it the Perennial Plant Association Plant of the Year for 2011. It wants full sun to part shade and is famously tough, adaptable, and deer-resistant, though it will flop open in too much shade or overly rich soil, so give it sun and a light shearing after bloom if you want it to stay upright.

Sweet iris (Iris pallida) is the plant behind orris root, and the first honest thing to say is that the romance and the garden plant are two different subjects. Orris is the aged rhizome of this species: the roots are lifted at around three years, peeled, dried and then stored for years more, and only during that long slow cure do the odourless triterpenoid precursors in the tissue oxidise into the irones that smell of violets, face powder and warm wood. Wikipedia's orris-root account puts the ageing at five years or more for perfumery grade against two to three months for potpourri, and the yield at roughly two kilograms of orris butter per tonne of root, the volatile fraction being 0.1 to 0.2 percent. That is why orris is one of the most expensive materials in perfumery, why it turns up as a fixative in fine fragrance and as a botanical in gin, and why nothing you do with a garden clump will reproduce it. What the garden actually gets is the second reason to grow this species, and it is the better one: silvery grey-green glaucous fans, to about 24 inches, that stay upright and presentable right through summer, which is precisely what most bearded irises cannot manage once the flowers are gone and the foliage browns and flops. The flowers are pale lavender-blue with yellow beards on sparsely branched scapes in May and June, and genuinely sweetly scented rather than merely fragrant on paper. Three caveats. Almost everything sold under this name is a variegated cultivar - 'Variegata', 'Argentea Variegata' - grown for foliage, not the straight species. It is a BEARDED iris, so the rhizome sits at or above the soil surface and rots if you bury it or mulch over it, which puts it in direct opposition to the water irises in this group. And in eastern North America the iris borer will find it.

A large, hairy, clump-forming North American native perennial of wet meadows, low woods, stream banks, and prairies. Its most distinctive feature is the perfoliate foliage - pairs of wrinkled, opposite, lance-shaped leaves whose bases fuse around the hairy stem, so the stem appears to pass through the leaf. From July to September, flat-topped clusters of small, fluffy white flowers feed a wide range of bees, butterflies, and other pollinators, while all parts of the plant are toxic and bitter.

Bergenia cordifolia (often treated by botanists as a synonym within B. crassifolia) is a tough, evergreen perennial native to the Altai Mountains, southern Siberia and Mongolia, grown for its bold, heart-shaped leathery leaves that flush red-bronze through winter and its deep pink flower spikes in early-to-mid spring. It is one of the most tolerant groundcovers in cultivation - enduring deep shade, poor soil, drought, and hard continental cold (commonly rated to USDA Zone 3 in US horticulture; RHS rates it H7, hardy below -4°F). The honest catch is its shallowly creeping rhizomes: in mild, moist climates they can colonise well beyond the intended planting, and the large, persistent leaves trap fallen debris and are notoriously attractive to slugs and vine weevils.

Liriope muscari is an evergreen, grass-like perennial native to the shady forest understories of China, Japan, and Korea, where it grows at elevations of 330 to 4,600 feet. In gardens it forms dense, weed-suppressing clumps of arching dark-green foliage topped by spikes of lilac-purple flowers in late summer, followed by ornamental black berries - earning it the RHS Award of Garden Merit. It is drought-tolerant and remarkably adaptable, but the honest catch is its behaviour outside its native range: in parts of the eastern United States it is a documented invasive species, spreading by rhizomes and self-seeding into natural areas, and it provides minimal wildlife value compared with native groundcover alternatives.

Creeping cotoneaster is a deciduous spreading shrub native to the mountains of central and southwestern China, Nepal, and Taiwan, prized for its distinctive flat herringbone branching, tiny pink-white summer flowers, and masses of vivid red autumn berries that sustain birds through winter. It holds the RHS Award of Garden Merit and tolerates poor, dry soils on banks and walls where little else will perform. The honest catch is twofold: the berries are mildly toxic to humans and pets (cyanogenic seeds, GI-irritant flesh), and the plant self-seeds freely enough that it is naturalising widely in the UK and Ireland and is considered potentially invasive - a real concern before planting near wild margins or hedgerows.