A good source for understanding the way hybridizers register for bloom season and other traits is the Registration Guidelines.
http://www.daylilies.org/AHSre...
For calculating bloom season there is a guide which spaces out when a cultivar has it's FFO (First Flower Open) or begins blooming. From EE to VL is a stretch of approximately 8 - 9 weeks, a big difference if you are looking for cultivars to begin the season or end it.
From the Registration Guidelines.....
"* SEASON OF BLOOM
Bloom season begins with the first cultivar to bloom, and ends when the last cultivar begins blooming. Bloom season is a bell curve, with the largest number of daylilies commencing bloom in the middle of the season. This is identified as MID-SEASON or PEAK BLOOM. Other bloom season dates approximate a time frame on either side of mid-season. Do not consider rebloom when determining bloom season. Calculate when peak bloom is in your area and determine how your seedling falls into the bloom sequence.
Use the following symbols:
EE - Extra Early.
A very few daylilies commence bloom earlier then 2-4 weeks before mid-season. These are Extra Early.
E - Early.
Daylilies that commence bloom 2-4 weeks before mid-season are considered Early.
EM - Early Midseason.
Daylilies that commence bloom 1-2 weeks before mid-season are Early-Mid.
M - Midseason.
Daylilies that commence bloom at "peak bloom" time are Mid.
ML - Late Midseason.
Daylilies that commence bloom 1-2 weeks after mid-season bloom are Mid-Late.
L - Late.
Daylilies that commence bloom 2-4 weeks after mid-season are considered Late.
VL - Very Late.
A very few daylilies commence bloom later than 2-4 weeks after mid-season. These are Very Late."
I also record the FFO on the cultivars in the garden each year. Early morning I take a notebook out with me and as I'm walking write down each cultivar showing an FFO for that date. I use a notebook because I also might record other notes, branching, etc. Later in the evening I transfer the FFO dates to an excel sheet with all the registered cultivars for that year. There is a third record that I do during the winter that includes each cultivar's FFO with each year it has been in the garden. This tracks the FFO habit by years.
