Harvest bittersweet when the first yellowish capsules of the fruit split open and you see the orange-red fruit inside. Cut stems to the length you desire, tie them together into small bundles, and hang them upside down in a warm, dry location out of direct sun. As the fruits dry, more unopened capsules will split to reveal the fruits inside. Bittersweet can self-sow and produce plants everywhere. If you have plants where you don't want them, pull them out or transplant them in spring to a more suitable location. Bittersweet produces separate male and female plants, so you'll need at least one male plant nearby to pollinate female plants for the berries. Unfortunately there's no way to determine the sex of an immature plant, so plant several vines to ensure that you have at least one male among your plants.