Here is a list of the latest blooming, longest lasting registered lilies we currently grow. All varieties on this list are asiatic or asiatic cross hybrids. List currently needs updating as it was last modified in about 2006!
You must realize that this list applies to average bloom times for these varieties in my garden - yours may be completely different, even if you are just a few miles away. How can this be? It all depends on trees, buildings, terrain such as slopes or flat land which all affect the microclimate in every garden. It is not uncommon to have a zone 5 microclimate in a typical zone 3 area, when extra protection such as buildings, trees, wind blocks, heavy snow cover in winter (like right beside your steps where you always shovel) are provided or nearby.
Weather patterns year to year make a difference too; an early spring can mean earlier than normal blooming overall. A normal spring with a heat wave lasting 1-2 weeks at end of June or beginning of July will push bloom to appear sooner than normal. A colder than normal spring that extends into June can delay blooming, just like drought or lack of adequate moisture can do the same.
I'm still trying to figure out various weather pattterns and how they affect the lilies, but like everything else with weather it is highly unpredictable! For example, in 2013 we saw some varied bloom periods that were baffling in some cases. We had a ton of snow very early in Fall 2012, which remained all winter long and as a result the ground was not frozen under it all winter long. The lilies all responded by coming up sooner than normal which was expected, but for the first time the OT varieties were sprouting the same time as everything else, when they are normally a week or 3 behind. Their earlier appearance lead to them blooming sooner than their average. Typically they are the last class of lilies going strong here from mid August to mid September but summer of 2013 saw them finish only a week or so later than the latest asiatics, and that is probably related to the fact that they last longer or they would have been done the same time. There appeared to be no rhyme or reason to the blooming of the asiatics as we had late bloomers blooming the same time as early short varieties, and early short varieties blooming mid season. As with most things gardening, just when you think you have something figured out, you realize you don't! So take this list with a grain of salt and don't expect that anything listed here will for sure, every year without fail, bloom later or earlier than anything not listed here.
Port Alberni Tiger