Question: Why do dandelions often rebloom in the fall?
Answer: Dandelions (Taraxacum officinale) bloom massively between March and mid-June in most parts of the northern hemisphere, covering fields and lawns beautiful bright yellow flowers, but cease flowering during the summer. Then they often bloom again, at least to some degree, in the fall. Why?
Various studies suggest that the bloom of dandelions is mostly influenced by a combination of day length and temperature. Flowering is initiated by days 12 to 13 hours long, but then the buds actually mature and open more or less quickly as temperatures warm up, usually blooming most heavily when the average daily temperature reaches 60˚F (16˚C). That’s why they can start blooming massively as early as March in warmer regions but as late as June in colder ones.
When the days are long in the middle of summer, no flower initiation normally takes place, but in the fall, when the days shorten to between 12 and 13 hours again, they often bloom a second time; that is, if the weather permits. This second flowering either peters out as days shorten further or ceases with the first severe frosts.