A large aster for wetlands and rain gardens, Swamp Aster easily reaches five feet high in the right conditions. Found in prairie and savanna situations, it thrives in wet to wet-mesic soils. Large pale blue daisy flowers with delicate petals are set in panicles beginning in late summer. Asters are key pollinator plants that provide a welcome source of late-season nectar. Numerous moths use them as larval hosts.