Forget the flowers. Everything you need is in your own backyard.
Leave the flower garden alone, and simply trim a bunch of leaves and grass from your yard. Gather different shapes and shades, such as fern fronds, palm branches, and holly and magnolia leaves. For a centerpiece, arrange the tallest green pieces in a cylindrical glass vase, and then place the vase in a tray of wheatgrass.
Arrange white pillar and votive candles around the table. (Place them in glass jars on windy days.) Tuck leaves underneath the candles, or tie grass stems around their centers.