This huge but slightly odd genus offers multiple choices for the rock garden or alpine house, says Miranda Kimberley.

S. striatum - image: Floramedia
S. striatum - image: Floramedia

Sisyrinchium is a bit of an odd genus. One species suits the herbaceous border and is the only one that is really well-known — S. striatum, with its pale-yellow flowers. But it is a huge genus, with between 90 and 140 species classified.

There are many choice species for the rock garden or alpine house, generally lower-growing than striatum but still pretty hardy in a cool, temperate climate, although there are a few species that do require protection.

They are small to medium-sized herbaceous perennials or rarely annuals with fibrous or fleshy roots, usually arising from a short rhizome. They are found in North, South and Central America with one species in Greenland and one in Ireland.

Part of the iris family, close relatives include Libertia and Olsynium. The leaves can be either sword-shaped like iris or grass like, with flowers that are purple to blue, yellow or occasionally white. The star-, cup- or trumpet-shaped flowers come in spring or summer.

S. striatum, with its popular cultivar ‘Aunt May’, a form with nicely variegated leaves, is certainly the most well-known species in cultivation. It is a strong-growing plant for the mixed or herbaceous border, providing medium to tall structural interest. It is semi-evergreen and likes full sun.

There are quite a few other hardy species though that are smaller in stature. One is S. idahoense ‘Album’,
a low-growing variety with stiff, grey-green leaves and open starry white flowers with a yellow throat.

Another is the Irish native S. angustifolium, which has slender green leaves that are still iris-like in appearance and bright-blue star-shaped flowers with yellow centres from late spring. It is naturalised across Europe. 

S. californicum brings the sunshine of California to us with its cheery, bright-yellow, star-shaped flowers. There are several nice varieties that may have inherited the lovely colouring of S. micranthum, with their purply-brown eyes or streaking, among them the rather oddly named S. ‘Quaint and Queer’.

Most of the Sisyrinchium in cultivation can be grown outside, with the exception of S. convolutum, which needs a minimum of 10°C.

S. angustifolium, S. micranthum and S. chilense need the protection of the cold glasshouse or alpine house because they do not cope when the temperature drops below freezing.

S. idahoense and S. montanum are the toughest of the genus, thriving even down to -20°C.

Ideally, you should plant Sisyrinchium in full sun, although most will tolerate shade for some of the day. They prefer a freely draining, sandy loam soil, incorporating additional organic matter such as leaf mould. S. bellum, S. californicum and S. angustifolium are best on moist soils but like it well-drained.

Species such as S. angustifolium and S. bellum will self seed if conditions suit. Propagate by seed in spring or autumn or by division in early spring.

S. angustifolium - image: Floramedia

What the specialists say

Sarah Conibear, owner, Westcountry Nurseries, Devon

"Sisyrinchium is a useful little plant, opening in the sunshine, providing a delicate blue colour not found in many flowers. Commonly called Californian blue-eyed grass, from the iris family, this genus of about 90 species is native to America.

"They are rhizomatous, semi-evergreen and compact, producing clumps of short iris-like foliage in a fan shape with many flattened, sword-like winged stems bearing clusters of large star-shaped flowers, each with a yellow eye. Little blooms are produced in April and May.

"They need to be planted in a sunny, well-drained, neutral to alkaline soil but not in a dry position. I like S. ‘Devon Skies’.

S. angustifolium is another excellent blue, while S. arenarium is the yellow-flowered form. All make good ground cover and are easy to grow, with few problems."

S. californicum - image: Floramedia

In practice

John Winterson, deputy buyer, RHS Plant Centres

"We sell a small range of Sisyrinchium with the most popular being the small plants sold from
our alpine sections. ‘EK Balls’ is the most popular, making a neat tuft with very pretty mauve-purple flowers. This, along with ‘Devon Skies’ and ‘Californian Skies’ are sold from our alpines A-Z section as well as from tables with blocks of plants in flower for impulse sales. They are easy to grow and have a decent flowering period, which makes them easy to maintain on the planteria.

"Our next most popular is S. striatum, which are sold in two- or three-litre pots from our herbaceous perennial section. The straw-yellow flowers look impressive up the grass-like stems, making a great feature for your garden. A block in colour on the beds attracts the customers to them and, again, they are easy to maintain. It used to be a strong seller but seems to be harder to get hold of nowadays."

S. ‘Devon Skies’ - image: Floramedia

Species and varieties

S. angustifolium, or stout blue-eyed grass, has bright-blue star-shaped flowers with yellow centres in May and June along with fine, semi-evergreen, iris-like foliage. Height: 30cm.

S. ‘Californian Skies’ is a short perennial with tufts of upright grass-like foliage and clusters of starry, clear sky-blue flowers with a dark throat and yellow eye all summer. Height: 20cm.

S. californicum has grey-green sword-shaped leaves and starry bright-yellow flowers in late spring or summer that sometimes turn orange as they dry. Height: 40cm.

S. convolutum is a pretty South American species with bright-yellow flowers between June and August. Height: 20-50cm.

S. ‘Devon Skies’ is a cute little plant that forms a low clump of grassy green leaves, bearing soft
sky-blue flowers in late spring with a dark-blue throat and yellow eye. Valuable in the rock garden as
well as for edging in the border.

S. idahoense var. bellum is an American species that forms a low clump of grassy green leaves, bearing starry violet-blue flowers with a tiny golden eye. Will tolerate moist to wet locations. Height: 15cm. Spread: 20cm.
S. idahoense var. macounii ‘Album’ Award of Garden Merit has stiff, grey-green leaves and open starry white flowers with a yellow throat. Height: 12cm. Spread: 15cm.

S. ‘Janet Denman’ is a lovely low plant with narrow, upright variegated foliage topped with creamy flowers that have a yellow centre and gorgeous purple striping. Height and spread: 20cm.

S. ‘Marion’ is a recent introduction that features large lavender-purple blooms, the petals streaked with a darker shade and a yellow centre. A vigorous, freely flowering selection. Height: 15cm. Spread: 30cm.

S. micranthum features white or blue flowers with yellow centres and an attractive purply-brown eye or streaking.

S. palmifolium is also known as the "bird-of-paradise" Sisyrinchium because it produces clusters of bright-yellow, star-shaped flowers at the end of the branching flower stems, over a long period of time. Height: 38-45cm.

S. ‘Quaint and Queer’ has stiff branching stems that sprawl around with creamy flowers that have pinky-brown markings and yellow centres. Flowers throughout midsummer to autumn. Height: 38 cm.

S. ‘Raspberry’ is a clump-forming perennial with narrow dark-green leaves. It has upright stems topped with pretty matt yellow and reddish/purple-veined flowers in summer. Height: 18cm. Spread: 15cm.

S. striatum, the yellow Mexican satin flower, is a clump-forming perennial with fans of grey-green, narrow, linear to lance-shaped leaves. In summer, stiff upright stems carry clusters of pale-yellow, star-shaped flowers along their length. Height: 40-80cm.
S. striatum ‘Aunt May’ is a very popular pale-yellow-flowered form of Sisyrinchium that flowers in the summer and has iris-like grey-green leaves boldly striped with creamy yellow. Less vigorous than the species and will not set seed. Height: 50cm. Spread: 25cm.

Thank you to Floramedia, which supplied the images afor this article from its photo library

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