Sunflower
in the cotyledon stage have survived temperatures down to 23°F. At later stages freezing
temperatures may injure the crop. Temperatures less than 28°F are required to kill
maturing sunflower plants.
Optimum temperatures for growth are 70 to 78°F, but a wider range of temperatures (64
to 91°F) show little effect on productivity. Extremely high temperatures have been shown
to lower oil percentage, seed fill and germination.
Sunflower is often classified as insensitive to daylength, and photoperiod seems to be
unimportant in choosing a planting date or production area in the temperate regions of
North America. Oil from northern regions tends to be higher in linoleic acid and has a
higher ratio of polyunsaturated to saturated fatty acids than oil produced in southern
latitudes.
Sunflower is an inefficient user of water, as measured by the amount of water transpired
per gram of plant above-ground dry matter. Levels were 577 (g H2O/g DM) for
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