Dahlias have become extremely diversified.Dahlias (Dahlia pinnata) are natives of central Mexico in the region of Mexico City. The early forms were mostly single flower types that grew on well-drained soils of volcanic origin. Because of their origin, dahlias require well-drained soils, fairly sunny locations, and, of course, proper fertilization and protection from pests. Dahlias provide one of the widest arrays of flower colors, sizes, and forms. Flower forms include daisy-like single types and fully double types with intermediate forms such as collarettes and anemone types. Dahlias come in nearly all flower colors except true blues. With centuries of hybridizing and selections. Dahlias are heavy feeders, so prepare the garden bed by spading or rototilling to a depth of as much as 8-10 inches. Working comport or manure into the garden will provide for a desirable slow release of nitrogen for dahlia growth. This is also a good time to work in a fertilizer such as 5-10-15 or 5-10-10. Apply it at about 2 pounds per hundred square feet. If soil tests indicate low pH, add lime (ground limestone) at this time also. Dahlias utilize large amounts of potash for root development, so add extra potassium if soil tests indicate low levels. Testing your garden soil is recommended procedure for dahlias and many other garden crops.