Native to Mexico, dahlias probably grew in Aztec gardens as they were already in cultivation when the Spaniards arrived.

Francisco Hernandez, a botanist and physician to King Phillip of Spain, described them in a book published in 1651. But dahlias were not introduced to Europe until 1789 when seeds were sent from Mexico to the Royal Gardens in Madrid. The flower was named in honor of Dr. Dahl a Swedish botanist and pupil of Linnaeus. They were sent to Kew Gardens in England in 1798 by the wife of the British Ambassador to Madrid. 

By 1835, John Wedgewood, the founder of the British Horticultural Society, grew over 200 different varieties of dahlias. They were popular cut flowers with blooms of many sizes and colors. 

If a tuber has a sprout of more than 2" long, clip it off before you plant the tuber. Dig a hole 4-6 inches deep and place the tuber on its side and cover it with soil. Fertilizer is needed every 3-4 weeks and must be low in nitrogen. Do not water until sprouts are visible above the ground and then water deeply 3 times a week. Full sun is best, but plant in part shade if your temperatures go over 100F degrees. 

Dahlias bloom about 3 months after planting. Cut blooms that are 2/3 open and place the stems in hot (but not boiling) water in a plastic container and leave them in it until the water cools.