Monday, February 11, 2013

Exploring the Mysteries of Bloom Season & Height: Rebloomers

by Betty Wilkerson


According to the American Iris Society, rebloomers must meet the same criteria that are stated for their individual classes.  My breeding program deals with tall bearded iris with the occasional cross in other classes.  The height qualification for tall bearded irises is 27 1/2" and above.  There is no upper limit stated, but an iris must stay in balance.  Many tall bearded irises have problems with falling stalks when the height is excessive. 

As you can see in this clump of 'Summer Radiance' (Wilkerson 96) there are stalks of various heights.  The stalks are measured from the ground to the top of the open bloom.  This should be done for a two year period.  The stated height is the average of these measurements in its home garden.

'Summer Radiance' (Wilkerson 96)  

As an introduction moves into the market, there will be some variations in the heights, and the iris may not reach these stated heights in the individual garden.  Soil contents, even micro elements, can change everything about an iris, including the height.  An early, hot season can create variations in height, too.

Spring Bloom Season

Tall bearded irises are the last of the bearded irises to bloom.  Season of bloom is designated within the tall bearded bloom season by VE for very early, E for early, M for medium, L for late and VL for very late.  These are determined in the garden of the hybridizer introducing them, and, based on my personal experience, may not be the same in your garden.  Again, VE means the iris should be one of the first tall bearded irises to bloom in your region and VL means the iris should be among the latest tall bearded irises to bloom.  These dates should be taken as suggestions, and may vary from garden to garden.  

It might seem that all rebloomers are very early (VE) to early (E) in the spring garden since they need time to bloom again, and indeed, most are.  'Star Gate' (Wilkerson 2005) is the only rebloomer I've introduced that isn't an early bloomer.  It blooms in mid season and can easily be used in breeding with later blooming spring only irises.  

'Star Gate' (Wilkerson 2005)  
As a hybridizer, you plan spring crosses during the winter.  The bloom season starts, but new acquisitions don't always bloom as hoped.  I rarely order very early irises because they can have a problem during a late freeze, although  I occasionally receive very early bonus irises.  So far, most of the new irises I've received with the VE classification are bloom EM in my garden.  

Rebloomers have pushed forward the beginning of spring bloom in my garden.  Here, tall bearded season begins with rebloomers and seedlings of mine that contain a lot of rebloom genes.  They will bloom for several days before regular spring blooming irises begin.  

In 2011 we had a light frost at the beginning of bloom season.  The blooms and pollen looked fine, but the pollen was damaged on open and nearly open blooms of 'Matrix' (Earl Hall by Lloyd Zurbrigg 1991)  'Echo Location' (Wilkerson 2007) and other open blooms.  When the frost hit, there were ten to fifteen stalks with open blooms on 'Lunar Whitewash'.  Crosses I made with this pollen did not take.  These are the difficulties faced by hybridizers working with early bloomers. It was three or four days before viable pollen was available.  

'Matrix' (Earl Hall by Lloyd Zurbrigg 1991)

'Echo Location' (Wilkerson 2007)

'Lunar Whitewash' (Sterling Innerst 2003)

By the time the late blooming irises are open, most of the rebloomers have finished blooming.  It’s hard to find anything other than ‘Star Gate’ to combine with late irises like ‘Iconic,’ ‘Haunted Heart,’ ‘Love Lines,’ or ‘Angel Among Us.’ Pollen from rebloomers can be stored in envelopes in the refrigerator for several weeks, but it’s such a busy time it’s often hard to remember to collect it!  

'Iconic' (Ghio 2010) Photo by Kent Pfeiffer

'Haunted Heart' (Keppel 2010)

'Love Lines' (Wilkerson 2006)

'Angel Among Us' (Wilkerson 2007)

Rebloom Season

My favorite rebloomers can bloom any time from the end of spring bloom until a killing frost.  To my knowledge, there is no correlation between the spring bloom season and the rebloom dates.  Rebloom can happen at any time and is determined by the genes of the cultivar, soil conditions, and weather conditions. There are only a few that can do this in my zone 6 garden during a normal season.  A few more can summer bloom in a moderate year, but few produce summer blooms in a hot and dry summer.  Cycle rebloomers are not genetically capable of summer rebloom and only rebloom in the fall when the temperatures cool and some fall rain has fallen.  

Additional information can be found at the American Iris Society website and the Reblooming Iris Society website.  Membership in the latter includes twice yearly publications called 'The Recorder.'  This publication reports rebloom from all over the continental U. S. and any other area that reports to them.

When do your rebloomers bloom?  Have you had summer as well as fall rebloom in your part of the country or the world? 


  1. BONSOIR de très belles fleurs j'aime aussi ces iris mais je ne vois pas toutes ces superbes couleurs ici


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