I don’t pretend to understand the environmental factors that determine when flower buds are formed on plants, or how quickly reblooming plants reset flower buds. It seems that temperature is the primary influence for many plants to set flower buds, but other plants are more effected by hours of daylight.
I’m quite certain that I’ve heard someone (or lots of someones) declare for the past fifty years that whatever year we’re in has had the most unusual weather ever. Of course, there’s always something peculiar about that year’s weather, but by year’s end most are very average. Except this year! In this statistically warmest year ever, far above average winter and early spring temperatures have caused many plants to flower weeks ahead of schedule, and for plants that rebloom this has added complications.
In last year’s unusually mild late autumn Encore azaleas flowered through November, and ‘Autumn Amethyst’ had a few blooms remaining in early December in my northwestern Virginia garden. Still, the Encores set new buds to flower in late March, a month earlier than normal. In the deep south Encore azaleas flower early enough that they often reset buds to bloom again in mid summer, and then again in the autumn, but in more northern areas they flower in the spring and again in late summer extending into early autumn.
In early August the flowers on ‘Autumn Twist’ are struggling with the extreme heat. ‘Twist’ is the most dependable and longest lasting autumn bloomer in my garden, but the flowers melt quickly in one hundred degree heat. Occasionally, I’ve had flowers on a few Encores late in the month, but these are several weeks early. Fortunately, other Encores are not flowering yet, so there will still be a good floral display in September and October. Is ‘Twist’ flowering early enough to reset buds by late autumn? Perhaps if November and December are as warm as the months were last year, but I wouldn’t bet on it.
The reblooming hydrangeas typically flower late in the spring, and often have sporadic blooms through the summer. With the extreme heat this year they have been slow to reset buds for the late summer bloom, so I expect this will be a bit later this year than is usual. I’m quite certain that the lack of bud set is a result of the hot temperatures. In a few mild summers the hydrangeas have reset buds to flower through July and August, but this year blooms have been scarce in the summer months.
In the past week temperatures have turned a bit more moderate and rainfall has picked up, so I expect the hydrangeas to get going setting buds that will flower late in September, only a little tardy. With less severe heat the Encore azaleas with fat buds but no flowers are likely to pop into bloom very soon.