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Featured Conservation Plants: October 2014

October 2014:
Iris x robusta ‘Dark Aura’

Iris x robusta is the name given to hybrids between Iris versicolor and Iris virginica. It was registered under the name x robusta because that group have low fertility, setting little seed. Although ‘Dark Aura’ does produce seed there is no evidence on its viability. Jenifer Hewitt – HPS member and Iris breeder introduced the plant originally under the informal name ‘Virginica de Luxe’ and it was first listed under that name by a German nursery (Friesland Stauden Garten) and was then registered as ‘Virginica de Luxe’ in 1987 with the American Iris Society.

However it was later discovered that the name was invalid according to the International Code of Nomenclature for Cultivated Plants (ICNCP) and in 1996 it was re-registered as ‘Dark Aura’ and attributed to Iris x robusta.

The new foliage in Spring is deep purple-red then leaf tips soon become green but as summer progresses the leaves develop purple-red bases. Flower stems are purple-black and flowers are rich purple with white signals on the falls. Stems grow to just under a metre (3ft) high given the right conditions and these are branched, carrying 4-5 flowers opening in succession. It is clump-forming and presents an attractive feature with such a combination of leaves, stems and flowers.

It performs best when planted in 5-10cm (2-4ins) of water but can be grown in soil that does not dry out or in a bog garden although growth may be slower and resulting height different from that stated.

Neutral to acid soil types also suit it best as chlorosis (yellowing of leaves) is likely if grown under alkaline conditions.

In order for the plant to be true to its registered name it must be propagated vegetatively as any seedling that may arise may not come true to the parent plant.

Division is the best method for propagation but does not necessarily have to be done immediately after flowering. What is important is that the plant is only propagated when the clump is big enough and the new divisions taken off the main plant should have at least 2 and preferably 3 rhyzomes not singles otherwise they may not survive. It is also important that the new divisions are kept moist and not allowed to dry out.


The Conservation scheme involves HPS members in growing these plants and documenting the best way to grow and propagate them. The plants are distributed across the country with many local groups and individual growers being involved.

The scheme is open to all HPS members. More information about the scheme can be found here.

Since the present scheme started in 1998, we have been successful in conserving over 30 plant varieties that are, in our opinion, all worthy of being grown in British gardens. However, there are still a large number of potentially garden worthy plants in need of conservation.

If you are a interested in making this (or any other of our conservation plants) available on a commercial basis, please contact the National Coordinator.


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