Beardless Iris
Initially, Dr. Tomas and Christina Tamberg focused on tall bearded irises. However, the garden’s acidic soil proved less suitable for tall bearded irises, which also required frequent division to maintain vigor, leading to space constraints. As a result, the Tambergs shifted their efforts to beardless irises, for which the soil conditions were more favorable and breeding progress had been comparatively limited at the time.
Inspired by Currier McEwen in the United States, Dr. Tomas Tamberg began experiments with chromosome duplication using colchicine treatment. He successfully converted diploid Siberian irises to tetraploids. More significantly, he applied this technique to sterile diploid hybrids, restoring fertility in the resulting tetraploids. This approach enabled new crossbreeding possibilities and led to the creation of fertile tetraploids from four hybrid groups. His work also produced novel hybrid categories, including Chrysata, Chrytosa, and Chrythenica hybrids.
Sibtosa hybrids are interspecies crosses between Siberian iris (Iris sibirica) and Iris setosa. At the diploid level, such hybrids typically have an unbalanced chromosome count (e.g., 2n=33), rendering them sterile due to differing parental chromosome numbers. Dr. Tamberg’s tetraploid conversions restored fertility, allowing further breeding advancements within this group.
Decades of breeding have resulted in highly regarded beardless iris cultivars, particularly Siberian (Iris sibirica) hybrids (both diploid and tetraploid) and vigorous Sibtosa hybrids (tetraploid crosses involving Siberian and other beardless species, notably Iris setosa). These plants are valued for their beauty and performance in sunny garden locations.
Examples of beloved varieties planted at Lilla Frescati Koloniförening include:
Iris sibirica Hybrids (Diploid)
‘Kleiner Schmetterling’ (registered 2010)
‘Hohe Warte’ (registered 2001)
Sibirica Hybrids (Tetraploid)
‘Prussian Blue’ (registered 1993)
‘Plissee’ (registered 1995)
‘Lavendelwein’ (registered 2001)
‘Rauchblau’ (registered 2007)
‘Lavendelturm’ (registered 2017)
Sibtosa Hybrids (Tetraploid)
‘Lavender Landscape’ (registered 2011)
‘Berlin Magenta’ (registered 2014)
Dr. Tomas Tamberg has registered numerous Siberian iris and hybrid cultivars, many incorporating Berlin-related names, reflecting his long-term contributions to beardless iris breeding.
Further details on his work with beardless irises can be found at:
Tamberg’s own homepage under the section ’Iris breeding’ (in German):
https://tamberg.hier-im-netz.de/iris-zuchtung.htm
Tamberg entry in the Iris Encyclopedia of the American Iris Society:
wiki.irises.org
Image: Iris sibirica ’Rauchblau’ by Dr. Tomas Tamberg. Photographed in Stockholm.
