Effects of day length and temperature on flowering of summer and August-flowering chrysanthemums.
J. hort. Ass. Japan 21: 251-5
The results of experiments with summer-flowering chrysanthemums, which flower in June, and August-flowering chrysanthemums, which bloom from the end of July to the middle of September in the Tokyo district showed that both of them are able to differentiate flower buds and bloom normally, though slightly late, in long days, but, whereas summer-flowering varieties differentiate flower buds when the temperature rises above about 8 degrees C., August-flowering varieties need temperatures exceeding 12 degrees to 15 degrees C. for flower bud formation. The conclusion is reached that although these two kinds of chrysanthemum are both day-neutral, they differ in flowering season owing to different temperature requirements for flower bud formation.