Within one or two months, your vine should measure 6 to 10 feet and your first moonflowers should bloom. The first flowers will be small -- 3 to 5 inches across -- but eventually your moonflowers should measure up to 6 inches across. By late June or early July, the plant should be covered with blooms. Moonflowers may take five or six months to bloom after planting, which is why you should plant the seeds in late February or early March. Gather ripe seed pods after they turn brown, beginning in October.