All stalks produced a single flower from last-years multi-flower seeds. Back where we started from on height, hoping for few centimeters improvement next year -- HOWEVER the tallest 99" stalk collapsed from the weight of the flowers and the seeds were not muture. Not sure if they will sprout next year, or if I'll have to resort to the second tallest at 94". Since the experiment is to select for height and not other factors like sturdiness, next year I will stake the tallest stalks.
Very dry, hot year -- record number of days over 95°F / 35°C.
Only planted seeds from last year's tallest sunflower, and most sunflowers appear to be hybrid of last year's 2 varieties: striped seeds but with smaller, secondary flowers on most stalks.
First year. Planted "Jumbo" sunflower seeds from a single packet, but 2 varieties of sunflowers appeared: Jumbo sunflowers with a single flower per stalk, and smaller multi-flower sunflowers that yielded seeds with solid-black shells, unlike the striped shells of the jumbos that you see sold as foodstuffs.