Siberian Flag grows well planted in full sun, although it grows quite well in part shade. But do not count on abundant flowering then. The plant reliability depends on its modest requirement if it comes to soil: sand, chalk, clay or loam, they do not matter very much providing the roots get plenty of water during growing season. That is why it is better to opt for a good garden soil or enrich the growing site with well- rotted natural manure where the soil contains a lot of sand. Iris sibirica shows a natural affinity for water and looks great planted near ponds, streams or other water bodies, but the roots should not stay directly in water as such a situation might pretty soon question or even terminate the advertised eternal growth of Siberian Flag.
Iris sibirica forms dense clumps of leaves reaching 60-90 cm (2-3 ft) high. The clumps spread up to 1m (3 ft). Newly planted irises do not produce many flowers but well-established ones give a real show every season. But after a few years, when we can observe a hollow centre appear, it is a sign for us to divide the clumps. It should be done in late August or very early in the spring when the new leaves start to emerge.
As I wrote before, Siberian Flag is mainly appreciated for the the various tones and shades of the blue and purple colours. However, the pure white and yellow cultivars are also worth considering. You can try them out mixed with the blue ones and add some red, pink or yellow roses to create a unique garden landscape. And when the flowers are gone, switch your attention to handsome leaves and wait until they turn yellow. The next switch is only a few months ahead .