Arisumi looked at the effects of temperature on daylilies. Unfortunately he only looked at one cultivar but below is a photo of the effects of five temperatures on daylily growth.
The temperatures left to right were 55, 65, 75, 85 and 95F (click on the photo to see all five plants).
He described the effects of the different temperatures.
"At 55° F. growth was retarded and the plants did not attain maximum size during the experimental period. The plants were full grown in approximately 3 months at 65° and in 2 months at 75°. At 85° and 95° the plants grew rapidly during the first 3 to 4 weeks and then became progressively chlorotic and the older leaves dried prematurely.
and
"Except for 4 plants at 85° F, flowering was obtained only at 75°."
and
"None of the plants forced at 65° bloomed during the experimental period. However, when the experiment was discontinued on April 10, 50% of the plants brought in the greenhouse in November and December had immature flowering scapes. These plants bloomed from 2 to 3 weeks after April 10 when the prevailing temperature averaged 75°. From these bloom dates it can be reasoned that at 65° it would have required at least 170 days to first flower for plants forced in November and 140 days for those forced in December.
At 85° most of the flower buds were blasted and only a few misshapen flowers bloomed. The scapes were weak and about half the size of those formed at 75°."
"The flowers pollinated at 75° and 85° were maintained at the same temperature until the seeds were harvested. Most of the capsules matured within 40 to 50 days after pollination. Seed set was good at 75° and poor at 85°."
I would guess that the optimum temperature for daylilies is about 80F or less.
