The better the soil, the better your flowers will grow. Most plants do best with a loose, fertile loam, which is described as rich, dark brown and smells earthy. A fistful of loam will form a loose, friable (will crumble) ball when squeezed. Clay soils form a dense rock like ball. Light soil like sand will not form a ball at all, but trickles through the fingers. Both light and heavy clay soils can be made more loam-like by adding organic matter. Organic matter improves the soil's texture, helping heavy soils drain better and light soils hold more moisture, while adding nutrients. The amount of organic matter you need to add depends on the quality of the soil. If you already have loamy soil, you won't need to add much. Excellent sources of organic matter are aged compost, leaf mold (composted leaves) or rotted manure. These can be purchased or made with trimmings and leaves from your yard.
Becky Hamilton, Smith County Master Gardener
Texas Cooperative Extension
Landscape Index
Gardening Tips For NorthEast Texas Index
East Texas Piney Woods Gardening Home Page