[loubylou29]

I have some sunflowers and was going to put them out and thought I wonder if they may get damaged by any frosts.

[Sadgit]

I am thinking exactly the same.. I have about 20 mini sunflowers about 6 inches in the greenhouse at the mo

[Aunt Sally]

Sunflower is grown in many semi-arid regions of the world from Argentina to Canada and from central Africa into the Soviet Union. It is tolerant of both low and high temperatures but more tolerant to low temperatures. Sunflower seeds will germinate at 39°F, but temperatures of at least 46 to 50°F are required for satisfactory germination. Seeds are not affected by vernalization (cold) in the early germination stages. Seedlings 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.

Complete article here: http://www.ag.ndsu.edu/procrop/sun/sunfst09.htm