Iris sibirica Blue Moon

The 'Blue Moon' Iris sibirica, also known as Siberian Iris, offers graceful intense bluish-violet flowers, veined with dark purple and tinged with pale yellow at the base of the petals in May-June. This striking plant forms a vigorous clump of vertical, green-grey slender leaves that remain beautiful for months. This iris adapts to moist and sunny banks and can thrive in well-worked ordinary soil as long as it is not arid, requiring little maintenance.

The 'Blue Moon' Siberian Iris is a rhizomatous and deciduous perennial plant that forms upright clumps starting from spring. It belongs to the Iridaceae family. It is one of the many cultivars obtained from the Siberian Iris, native to central Europe, eastern Europe, and Turkey but absent from Siberia, and the Iris sanguinea, found in China, Siberia, Japan, Manchuria, and Korea. This iris can reach a height of 80cm (32in), 1m (3ft) when in bloom, and the clump will spread over 50cm (20in). Its growth rate is moderate, slower than that of the German Iris. The 'Blue Moon' Siberian Iris has an elegant upright habit with dense clumps. The foliage consists of long, narrow green-grey leaves. In late spring and early summer, the flower stems project above the foliage, bearing 3 sepals and 3 petals that arrange themselves and successively bloom from the top of the stem to the lower branches. They are a vivid bluish-violet, marked with yellow at the throat and veined with darker purple. This iris spreads through rhizomes.

The 'Blue Moon' Siberian Iris tolerates a wet location, such as a bank, as long as it is not permanently submerged. It can also be cultivated in regular garden soil with mulch and watering every 15 days in summer. It prefers an acidic to neutral soil (pH 4.5 to 8), rich and well-drained. Clayey, chalky, or sandy soil can be improved by adding a good amount of humus (well-decomposed organic matter). Alkaline soil can be slightly acidified by adding ericaceous soil, pine needles, or sulfur. Siberian irises need a sunny location to flower, with at least 6 hours of daily sunlight. In the hottest regions, light shading during the hot hours can be beneficial. It is best to plant during the dormant period, from late September to mid-April, avoiding freezing weather. In warm climates, planting can be done in September. In colder regions, planting should be done at the beginning of the growing season, in late March or April. (They will only flower the following year). Planting in August can be an alternative. Plant the Siberian iris rhizomes at a depth of 3-5cm (1-2in). Siberian irises can remain in place without division for longer than bearded irises. They should only be divided every 5 to 10 years when the clump no longer blooms in the centre or forms a crown. Sufficient space should be provided for good clump development. Fertilise with an NPK 10-10-10 type fertiliser at the start of the growing season and after flowering in June. On young clumps, systematically remove faded flower stalks to prevent exhaustion. On well-established clumps, remove the stalks to prevent spontaneous seeding of non-true seedlings around the mother plant. After autumn frosts, yellowing foliage can be cut back to 3-5cm (1-2in) from the ground (and left in place as mulch). Alternatively, this dry foliage can be left during winter as an "architectural" element in the garden. It should only be cut back at the end of winter, in late February, before the new leaves emerge.

In the edge of a water feature or stream, or simply in very moist soil, the 'Blue Moon' Siberian Iris is irreplaceable. It can also be used in any non-arid garden. Its grace is perfect for romantic gardens, English gardens, and other mixed borders. It can be associated with summer snowflakes, camassias, poet's narcissus, montbretias, crinums, daylilies, delphiniums, columbines, ligularias, phlox, asters, herbaceous peonies, and lady's mantle in moist soil.

Good to know: The wild Siberian Iris L. is an endangered and protected species that must be respected. Horticultural "Sibirica" irises are hybrids obtained from different species of the Sibiricae series (I. sanguinea, etc.). Their flowers are larger than those of wild forms and come in various colours. Several hundred named cultivars are registered.