Iris Is a Long-Day Plant That Normally Flowers in the Spring

Multiple Choice

Iris is a long-day plant that normally flowers in the spring. Which of the following regimens would be the most effective in making an iris bloom in late fall?

A) interrupting the plant's nights at 2:00 am with a flash of far-red light
B) interrupting the plant's nights at 2:00 am with a flash of red light followed by a flash of far-red light
C) interrupting the plant's nights at 2:00 am with a red flash, then a far-red flash, then a red flash
D) interrupting the plant's days at 2:00 pm by putting it in the dark