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Dahlias bloom about 8 weeks

Dahlias bloom about 8 weeks after planting. They prefer to planted in the spring so they hit flowering mid-July or so. However, they may flower for you by September or October before the frost. Otherwise, you could just put them in storage through the winter. Since you live in NY, you'll need to dig them up either way in the fall and store over the winter. Pack in sawdust or peat moss in a cool, dark place. Don't let them get moist or they'll rot.