Susan Iverson, a 66-year resident of Alaska, noticed a rose bush (Rosa acicularis) in her yard that bloomed in early September this year. She has noticed the roses blooming in September in her yard a few other times in the past 10 years. It seems like it just wants to keep on going! This year there were about 150 other buds still there, but only 2-3 that opened in September of 2017. Susan asked if there are chemicals being released by the plant that make the flowers want to keep going.
This observation was recorded with permission after a phone call with Susan, Jan 26, 2018.
Pamela Diggle with the University of Connecticut writes:
Plants rely on a variety of signals so that they go dormant at the right time. Going dormant at the right time is critical for flowers or leaves. If they delay too long, they risk being killed by low temperatures. The type of rose you saw typically begins to form its flowers in the summer, but those flowers go dormant and then expand into fully formed flowers the following spring. The flowers that you are seeing in the fall are not getting the appropriate signals to dormant. One of the goals of "late bloomers" is to understand what those signals are. Temperature is probably very important and temperatures probably do cause the plant to make some chemical signals, but those signals are not necessarily released by the plant into the environment. Rather, they remain inside the plant and cause the flowers to open prematurely.
Comments from LEO Editors:
LEO has received one other observation of a late-blooming rose, also in Fairbanks, during October of 2017. This observation has been added to the Late-Bloomers LEO Project, which is collecting observations of flowers blooming during late-summer and fall around Alaska, to better understand a possible interaction between warming temperatures and plant response. According to the US Forest Service Species Profile, Rosa acicularis typically blooms in June and July, and hips turn red in August.
Pictured below is three figures documenting temperature changes in Alaska. The Mean Annual Temperature Departure chart shows temperature variation trending toward warmer temperatures beginning around 1974. The Total Change in Mean Seasonal and Annual Temperature table breaks down the change in mean temperature by season between 1949-2016, showing warming winter temperatures. That same chart, but for a shorter time frame of 1977-2016, shows less drastic warming trends than the 1949-2016 time frame, but does show consistent seasonal temperature increases in northern Alaska communities such as Barrow, McGrath, and Kotzebue.
Mean Annual Temperature Departure for Alaska (1949-2016)