I have produced seeds by crossing an intermediate bearded iris with a tall bearded iris which haven't reached flowering size yet. I yielded 15 seeds, 9 germinated and one of those nine died.
In the 2015/16 Tempo Two catalog it says:
"Median bearded iris - or intermediates derive mostly from crossing Tall Bearded Iris (TBs) with Standard Dwarf Bearded Iris (SDBs). Because of the unusual chromosome numbers that result from these crosses, most varieties are sterile. However, as the bearded iris gene pool becomes more complicated with more generations of seedlings, some modern Intermediates are somewhat fertile. Often seedlings resulting from crossing these fertile varieties have many of their size proportions out of classification: either huge flowers on short stems or very small flowers on tall stems...."
