The general rule is to start your canna rhizomes indoors 4 to 6 weeks before the average last frost date in your area. For Washington County, the last frost date is still June 1st, so after mid April is the time to take them out of cool storage. The accepted storage temperature for dormancy is between 45 F and 55 F. Once they start to warm above that, they usually will quickly begin to grow.
Plant the cannas in large clean pots. The rhizomes should be covered with 3 to 4 inches of good sterile potting soil. Then move the transplants to a warm sunny location and water thoroughly as needed. Fertilize once the leaves appear and be sure to harden off the plants before moving them outdoors.