For most uses, harvest herb flowers just as they start to open. As with the rest of the plant, their freshness peaks and falls off quickly. Essential oils that provide flavor, fragrance, and healing qualities are all at their peak as the bud is swelling. Cut the flower off with a bit of stem (which helps keep flowers from falling apart) above the top set of leaves.

For dry arrangements, wreaths, or crafts in which you use entire flowers, you achieve a more natural-looking result if you pick flowers at different stages -- unopened, partially opened, and completely opened. Harvest them with at least 6 inches of stem. Potpourri, too, has a more interesting texture if you include a few tight buds along with petals. If you're going to press flowers, let them open a bit more before you cut them -- enough that you don't have to wrestle them to lay flat. After they've fully opened, don't leave them in the garden, where their color will fade, or where insects can damage them.