“Planting time is the trickiest. You can’t plant dahlias too early, when ground temps are still too cold. If it’s looking like a very damp, wet stretch, tubers are prone to rot. In the Northeast, early to mid-May is probably the best time, when the ground temp is about 60 degrees.”Light
“Dahlias like sunlight and should be planted in a sunny location: a minimum of 6 to 8 hours of sunlight a day. Any less and your plants won’t yield as many blooms.”Moisture“Because dahlia tubers are prone to rot, it’s important to make sure that the soil isn’t too heavy. It should drain freely and easily; if not, amend it with peat or sand. If the amended soil is damp, you won’t even need to water until the shoots start emerging.”Sourcing Dahlias
“Dahlia tubers are readily available from many growers online. Tubers are essentially the root stock of the dahlia plant and, once planted, will multiply in the ground every season. A dahlia plant grown from one tuber will yield multiple tubers once dug up in the fall.”Keeping Dahlias“In the Northeast, our winter temps are just too cold, and dahlias’ thin-skinned tubers will freeze. Tubers can be pulled each fall, cleaned, and stored in a cool, dark room until next spring. It’s best to dig them up a couple of weeks after a frost, when the tubers have hardened off.” Packing them in peat moss, wood shavings, or vermiculite in a plastic bag punctured with fine holes will keep them clean and dry.
For more information about growing dahlias, contact the American Dahlia Society: dahlia.org