Answer: What a great project! Sunflowers are warm season plants so you should plant them after all danger of frost is past and the soil is beginning to warm up (about the same time as local gardeners plant tomato and pepper plants). They grow perfectly well in average soil but should definitely be grown in full sun (at least six hours of sun a day). After they are up and growing, fertilize with a general garden fertilizer once a month. Don't be tempted to give them more fertilizer than the directions on the package, because it will cause the plant to produce more leaves, possibly at the expense of the flower.
In order to force a sunflower to make a huge flower, pinch off any side shoots that develop. And, be prepared to put up a substantial stake to support the plant. Since you are going to have a gigantic flower head, you may even need to be ready with some sort of support for the head itself. Have fun with this!
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