Exploring the Mysteries of Bloom Season & Height: Siberians

By Bob Hollingworth

It's really quite strange that we have never standardized how we communicate the bloom time or height for irises, even though these are required characteristics in registering an iris with AIS.  

The situation of bloom time as it refers to Siberians is exactly like the bearded irises as described by Jim Hedgecock in his recent post. To me the registration should indicate when this cultivar blooms in relation to other cultivars in the class, hence the E, M or L designations, maybe with a V(ery) added to indicate unusual earliness or lateness.  However, clearly some hybridizers use these terms not to indicate peak bloom time but duration of bloom with the designation EML, meaning, I suppose, that it starts early and blooms throughout the season and not that it can start bloom at any time in the season (which is quite unlikely, since relative bloom time is quite reliable with Siberians).

'Who's On First' (Hollingworth, 2008)

'China Spring' (Bauer-Coble, 1999)

The introduction of  I. typhifolia to US hybridizers about 20 years ago moved up the bloom season for Siberians since these typically bloom 2-3 weeks before the more familiar sanguinea/sibirica hybrids (although a few sibiricas can bloom quite early too). So the meaning of Early has changed a bit with time.  Cultivars with some I. typhifolia genes will likely bloom well before the pack, such as 'China Spring' and 'Who's On First,' or Dave Niswonger’s “China” series.  

The season used to end for us when derivatives of Bill McGarvey's later whites including heritage from 'Esther C. D. M.' and 'Gull’s Wing' opened up, such as 'Hooked Again'  or 'Blushing Violet' . But I believe we may have a new winner for latest to bloom - 'Pool Party'. The last two years this has bloomed for us so late you wondered if it would ever open - after many early cultivars were already bloomed out. However, this may not be typical since 'Pool Party' is registered as an ML bloomer not VL. We don’t grow 'Worth the Wait' (Schafer-Sacks, 2002) or 'Last Act' (McEwen, 1985), but the names suggest that they should be very late bloomers too.

'Hooked Again' (Jim Copeland, 2006)

'Blushing Violet' (Hollingworth, 2005)

'Pool Party' (Cole, 2008)

Unfortunately, it seems that nothing is ever that simple and there are a significant number of Siberians that repeat bloom (mostly rather sparsely) a few weeks after first bloom. If the repeat bloom period is clearly separated by a flowerless period, it is easy to characterize, but a few irises stagger along between these two seasons and never seem to be entirely out of bloom for several weeks. This characteristic probably this led to the most convoluted registration I know ('White Prelude', McEwen, 1993) which is registered as VE-EML-VL & RE!

Whether to indicate the “repeat” bloom in the registration (and advertising) is a matter of judgment for the hybridizer – but if this happens most years and gives a display that attracts attention, it certainly is justified. There is a genetic basis for this tendency.   Nevertheless, the nature and environmental conditions that govern "continuous bloom" and "repeat bloom" are still quite mysterious. It also seems that some Siberians repeat bloom more readily in some regions than others, which makes their characterization even more difficult.

Height is in some ways a bigger problem, since here we are giving absolute values (e.g. 25 inches) rather than relative ones (dwarf, median etc.) and of course this is going to vary from year to year and from place to place as growing conditions vary.  

With Siberians a good clump will often have blooms at several heights - shorter around the outside and taller in the middle.  This gives a desirable bouquet effect as seen in the photos above.  So which height to choose? And then again, the flower stems elongate during the bloom period and may end up several inches taller on the last blooms compared to the first ones.

I expect different hybridizers use different methods to handle this variability. I generally record the height of taller stalks (ground to top of flower) for several years before introduction and use the tallest year as the registration height. Why not the average? Because this way seems to me to best represent the genetic potential (under ideal  growing conditions) of the variety. What does everyone else do?

'My Little Sunshine' (Schafer-Sacks, 2010) 

In fact, since there are no size classes for Siberians as there are with bearded irises, exact height is not critical and it would be just as good to have relative classes for height as we do for bloom time.  Dwarf, median, and tall are convenient, but that’s not how the current system works, in part because “dwarf” has a specific meaning in the bearded world that does not translate to Siberians. We do have irises that regularly bloom much shorter than most others  ranging from the old sibirica nana alba (which is actually a sanguinea in all probability!) to more recent ones like 'My Little Sunshine' that bloom at around 12-15 inches.  Compare this to the giants of the Siberian world at 48 inches or taller!  Let’s leave  with the thought that the long and the short of the Siberian iris world might make a good topic for a future post.