Planting trillium flowers successfully can be difficult. Seeds take up to two years to germinate and must be sown immediately upon harvesting, making them impractical for most gardeners. Trillium also does not transplant well, although container-grown plants are found occasionally at garden centers. For the best results, plant and grow trillium from dormant rhizomes, which can be ordered from gardening mail-order establishments or purchased from nurseries. Once you get them started, trillium plants need almost no maintenance or care and will thrive under the right conditions.
Plant trillium rhizomes in late summer. Choose a planting site with moist, fertile, well-draining soil that receives filtered sunlight throughout the day. Trillium flowers are native to woodland areas, so planting beneath large deciduous trees in your yard is ideal.
Prepare the planting area by cultivating the soil to a depth of at least 6 inches. Use a garden tiller for large areas or a garden spade for smaller sites. Add a 1- to 2-inch layer of organic compost and incorporate into the soil before planting.
Dig planting holes for your trillium rhizomes about 24 inches apart and 2 to 4 inches deep. Place a rhizome inside each hole with the "eye" facing up, and then gently cover with soil. Water the area immediately to initiate growth and compact the soil.
Apply a 2- to 3-inch layer of mulch to the planting site to protect the newly planted rhizomes over winter. New growth will appear the following spring, usually around April, and continue through summer, although blooming will take several years.
Water trillium plants only if they are in an area that dries out during the hot summer months. Otherwise, they need no supplemental care and will soon colonize the area where they were planted, creating a thick, attractive ground cover.