Harvest sweet Annie in midsummer. Wait until you see tiny open blossoms along the branches; from a distance the plant will have a yellow cast. Sweet Annie harvested before the blossoms open will not be as attractive in arrangements and will taste bitter in a tea because the sugars would not be fully developed.
Snip only one or two sweet Annie branches from each plant. Harvesting too much could kill a plant. Cut the branches with pruning shears near the base of the plant. The stems will be thick and sturdy; force is necessary to successfully cut the branches.
Tie the cut ends of the branches together, putting no more than eight branches together in a bundle. Leave a long strand of twine hanging from the bundles. Gently gather a brown paper bag over each bundle. This will prevent you from losing dropped flowers and protect the branches from light.
Use the long twine to hang each bundle in a cool, dry place. A closet, dry basement or pantry are good choices. Leave the bundles alone for about two weeks. Check on them and touch the flowers. If the flowers are not brittle and crumbly, let them dry for another week.