Trillium undulatum is a perennial herbaceous plant that spreads by means of underground rhizomes. There are three large leaf-like bracts arranged in a whorl about a scape that rises directly from the rhizome. Bracts are ovate, each with a definite petiole.
As long as they have been planted in a suitable location, you need only keep the soil evenly moist, but not soggy. They may also require water in dry weather.