Effect of Planting Date
As expected, the earliest planted sunflowers (25-May) bloomed earliest, by 27-July. Sunflowers planted
on 1-June bloomed by 2-August and the latest planted sunflowers by 8-August. Essentially for every one
week delay in planting there was approximately a one-week delay in bloom.
The 1-June planting date resulted in a significantly higher plant population compared to the other dates
(Table 3). Having all been seeded at a rate of 32,000 seeds per acre, this means that the establishment
rates for the three planting dates varied from 53% to 81%. Sunflowers planted on the third planting date
(7-June) were the tallest (55.4 inches) and also had the widest seed head (7.5 inches).