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 regimen 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