Answer: Sunflower seeds should be planted after all danger of frost and when the soil temperature has had a chance to warm, otherwise they may rot in the ground. They may also rot if they are kept too wet. At my house, the birds and critters tend to steal the seed so that is another possible explanation. Other problems can be lack of water or uneven water because once the seeds have begun to swell they must not be allowed to dry out -- if they dry out they will die. Finally, it pays to prepare the seedbed thoroughly by incorporating plenty of organic matter and working the soil to a fine texture so there will be good seed to soil contact.
There are so many choices for planting a sunny spot I can't begin to make specific suggestions. Instead you might want to look at a book or two to help you with your planning. One I particularly like is "Gardening for Dummies" by Michael MacCaskey ISBN 1-56884-644-4. In it you will find many suggestions for plants to try as well as information about soil preparation and overall planning tips.
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