Iris

The classic German or common-flag iris - the presumed parent of most modern bearded-iris cultivars, probably native to southern Europe and the Mediterranean and naturalized widely. Each stalk carries up to six large, usually fragrant flowers in spring: three erect lilac standards above three purple falls marked with brown veins, white bases, and the signature yellow "beard." It has no bulb, spreading instead by creeping rhizomes that form large clumps, with sword-shaped basal foliage to about two feet.

A native eastern + central North American wetland iris producing striking violet-blue flowers with yellow + white throat markings in late spring + early summer. Tolerates wet feet better than most irises - among the best perennials for rain gardens, stream edges, and pond margins. Long-lived; clumps slowly expand. ALL parts of the plant are toxic (irisin glycoside) - wildlife typically avoid it; humans + pets can experience GI distress + skin irritation from sap contact.

A diminutive native woodland iris forming spreading mats of low sword-shaped foliage topped briefly in spring by delicate light-blue flowers with bold yellow + white "crests" running down each fall. One of the most charming native perennials for partly shaded sites. Among the smallest native irises (6-9" tall) - works beautifully as a groundcover under deciduous shrubs + along path edges. ALL parts toxic (typical iris caveat).

Iris ensata is a beardless water iris native to Japan, China, Korea, and the Russian Far East, prized for some of the most spectacular midsummer flowers in the perennial garden - wide, flat blooms in purples, whites, and bicolors on upright stems to 30 inches. Fifteen cultivars hold RHS Award of Garden Merit recognition, and Japanese breeders have refined three distinct strains (Edo, Higo, Ise) over five centuries. The honest catch is demanding site requirements: it needs consistently moist, reliably acidic soil (pH 5.5–6.5) and resents lime; even slightly alkaline or dry soil leads to chlorosis, poor bloom, and eventual decline, making it unforgiving in gardens with alkaline tap water or drought.

Two honest caveats before the good news. First, almost nothing sold as Siberian iris is this species: several hundred registered cultivars stand between the buyer and the wild plant, a great many of them hybrids with Iris sanguinea rather than Iris sibirica at all, so a garden centre label is a series name more than a binomial. Second, it is slow and it does not want your help. The Royal Horticultural Society gives two to five years to ultimate height, and the standing advice is to avoid dividing a clump unless the centre has actually died out - the opposite of the reflex most gardeners apply to perennials. There is also a quiet irony worth stating: a plant this common in gardens is Extinct in the Wild in Slovakia, Vulnerable in the Czech Republic, Hungary and Ukraine, and rare and endangered in Poland, because the wet hay meadows it belongs to have been drained. Now the good news, which is most of the record. This is the low-drama iris of the group. It is beardless, with a thin creeping rhizome about a centimetre thick rather than the fat surface knuckle of a bearded iris, and it is planted BURIED - rhizome tops 1 to 2 inches under the soil, exactly the depth that would rot Iris pallida. It wants ordinary good garden soil that stays moist through spring and early summer and is merely ordinary by August, so unlike Iris pseudacorus and Iris virginica in this wave it is not a water plant and will not thank you for a pond margin. Its narrow ribbed grassy foliage stays clean and upright all season where bearded-iris fans go rusty by July, it never needs staking, it is long-lived and clump-forming, and it carries far less of the iris borer burden that defines rhizomatous iris culture in eastern North America. If you want one iris out of this group and you want it to behave, this is the one.

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.

Virginia iris (Iris virginica) is a marsh plant, and the commonest way to fail with it is to buy it as a border perennial. Missouri Botanical Garden puts it in wet, boggy, acidic, sandy soil in full sun, rates its water need medium to wet, and lists water plant, rain garden and naturalise as its uses; the Lady Bird Johnson Wildflower Center rates water use High, soil moisture Wet, and CaCO3 tolerance LOW. Read together that is a plant which wants saturated ground or shallow standing water and dislikes lime, which is close to the inverse of an ordinary well-drained bed on builders' subsoil. Planted in one it does not die dramatically; it thins, stops flowering and fades out over three or four seasons, and the gardener concludes irises are difficult. Sited properly it is among the best things a pond margin can hold: 1 to 3 feet of bright medium-green sword foliage that often lies out over the water, and violet-blue flowers in late spring carrying a bright yellow, conspicuously HAIRY signal patch on each fall. That signal is also the field mark - Iris versicolor, its near-identical northern counterpart already in this catalog, carries a flatter greenish-yellow signal with few hairs and heavier purple veining. The reason to know this species specifically is the sibling it replaces. Iris pseudacorus, the yellow flag in this same wave and the same botanical series, is a European wetland iris that has escaped into North American marshes and is regulated as a noxious weed in several states. If you want an iris standing in water at a pond edge, this and Iris versicolor are the two answers that do not get out. Two cautions carry across the whole genus: the rhizomes contain irisin and iridin and cause vomiting and diarrhoea if eaten and dermatitis on handling, and iris borer (Macronoctua onusta) is the pest that decides whether a rhizomatous iris planting survives in eastern North America.

Yellow flag iris (Iris pseudacorus) is one of the most damaging aquatic invasive plants in North America, and this record exists mainly so you can identify it and decide whether to remove it. In Europe and northwest Africa it is a genuine native, a handsome 3-to-5-foot beardless water iris of ditches, fens and river margins, and one of only two irises native to Britain. Everywhere it was carried to as a pond ornamental it behaves differently. It builds rhizome mats that can connect several hundred flowering shoots into a single clone - clumps measured to 66 feet across in Ireland - and those mats trap sediment, narrow stream channels, choke irrigation ditches and dry a marsh out from underneath. On Theodore Roosevelt Island it replaced native green arrow arum, the wood-duck food plant, and suppressed willows; in Massachusetts it displaced two native irises; in Californian marshes it took over from cattail. The seed floats, and floats for a long time: essentially all of it is still afloat after a week and a quarter of it after a year, so one garden pond seeds a whole watershed downstream. It is listed as noxious, prohibited or invasive in Washington, Oregon, Montana, Connecticut, Massachusetts, New Hampshire and Wisconsin among others, and as a provincial noxious weed in British Columbia, yet it is still sold as a pond plant in places where no rule bans it. Missouri Botanical Garden carries the flag on its own page - listed as a noxious weed in one or more Midwestern states, should not be moved or grown where dissemination is a danger - and tells readers outright not to plant it along streams, ponds or lakes. If what you wanted was a tall yellow-and-green vertical at a pond edge in eastern North America, plant Iris virginica instead: same beardless water-iris architecture, same wet feet, native. And handle this one with gloves either way, because the rhizome and sap are poisonous and blister some people's skin.