Answer: In sandy soil, the most important thing you can do is to add organic matter such as compost. This will help the soil to hold moisture and nutrients better. Also be sure to use an organic mulch year round. This will help reduce the need for watering and will also help feed the soil and provide organic matter as it breaks down over time.
For a full sun location, you might try perennials such as yarrow (Achillea), sea thrift (Armeria maritima), Baptisia, Dianthus, poppies (Papaver orientale), blacy-eyed Susan (Rudbeckia fulgida), perennial salvias, and sedums.
Some annuals to try would include marigold, zinnia, cleome, and annual salvias.
I hope this gives you some ideas.
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