You can build populations of desirable “weeds;” for example, native petunia (Ruellia humilis), pink evening primrose (Oenothera speciosa), wild columbine (Aquilegia canadensis), Blue mist flower (Conoclinium coelestinum), or Plains coreopsis (Coreopsis tinctoria) are all ecologically valuable self-sowers that will move around in a garden and fill gaps.