It is interesting in fact, to see that this particular Iris prefers to be in the shade.
If you take a short walk through the Dunedin Botanic Gardens' Azalea Garden to the top of the Cherry Walk you will see one patch of I. japonica growing in open sun.
In this situation the leaves are yellowish green and the flowers too are bleached with faded markings and smaller in size compared with those growing in the shade of some large rhododendrons only a few metres to the left.
Flourishing in shade
In the shadier position, the rhizomes sprout fans of three or four dark, glossy, evergreen leaves up to 60cm long and spread through their allotted space to form a lax, undulating ground cover punctuated by the upward-pointing blades of younger leaves.
Stiff, narrowly branched flower stalks rise above the foliage in early October and unfurl a succession of delicately frilled white blooms, tinged lilac with darker mauve spotting.
Contrasting with these more subtle tones is a golden yellow crest in the centre of the falls.
Appealing contrasts
For me, the overall appeal of Iris japonica lies in its combination of contrasting features - the lax and upright foliage, the gold against mauve on the flowers and the way that they are held in an airy scattering above the dark mass of foliage below.
In turn, the narrow pointed leaves and relatively small flowers contrast with the bold foliage of large-leaf rhododendrons forming the backdrop.
Ideally, Iris japonica requires semi-shade in well-drained soil and does not need much feeding.
However, it grows in various positions in the botanic garden's Rhododendron Dell that range from free-draining loam to heavy waterlogged clay, as long as its rhizomes have a surface layer of compost to spread through.
Doug Thomson is Dunedin Botanic Garden Rhododendron Dell curator.
