>>1109024That's about right. I harvested mine when the back side was starting to turn yellow and the petals were withered brown (pic related). Though, the length of time is dependent on the cultivar. The trick is to plant a new set of sunflowers every week for a few weeks. Then you have continued overlapping blooming for quite a while. This is done with several flower/vegetable types. However, some plants can't be done like that since their life cycle changes are triggered by temperature changes and/or daylight length (all of them end up blooming at the same time regardless of when planted; like lamb's quarter).
