Superbloom occurs only about once every decade or so. It is very unpredictable though. It can happen for two or even three consecutive springs. Alternatively, it may not happen for two decades. It can be as early as late February, or as late as late May. It can last one or a few weeks. Superbloom is as variable as the environmental factors that influence it.

Actually, all bloom relies on influence from variable environmental factors. That is how it knows how and when to bloom. It is also why many species are so irregular about doing so. Various species prioritize reliance on various environmental factors. Therefore, some may bloom early or late while others adhere to stricter schedules. It can get complicated.

Warmth is undeniably the most significant of environmental factors that influence bloom. Cool weather inhibits bloom, even as growth resumes at the end of winter. Then, warmth accelerates bloom, mostly during spring, but also into summer. Many species continue to bloom as long as the weather stays warm. Very few prefer to bloom during cool weather.

As mentioned, the influence of environmental factors can get complicated. Many species actually require sustained winter chill, or vernalization, to bloom well. It is how they reset their growth seasons to begin in winter. Peony is unreliable here because of inadequate chill. After unusually cool winter weather though, flowering cherry and lilac bloom better.

Humidity is another important environmental factor. Although it does not stimulate bloom for more than a few species, it can prolong bloom. Some flowers, particularly from humid climates, can desiccate with aridity. Conversely, even flowers from desert climates retain hydration better with humidity. Also, rain provides water for areas that lack any irrigation.

Species from mild but not tropical climates might rely more on photoperiod than weather. Poinsettia in the wild does not experience sufficient chill to distinguish winter. It monitors the photoperiod, which is the duration of daylight, instead. It knows to bloom when nights are longer than days. A few species use the same very consistent technique to bloom for other seasons.