In the shade garden, plant them in compost amended soil in groups. Again, don't plant them near other perennials that might overtake them in time. Some good companions in the flower garden include any of the other spring ephemeral flowers such as trout lilies, foam flowers, woodland phlox,solomon's seal andcolumbine They also look beautiful planted near narcissus, Siberian squill and Species Tulips.
Overwintered primulas, pansies and violas often will be in full bloom when trilliums are flowering and these shade lovers compliment the trillium flowers well.
Some shade perennials have colorful or interesting foliage that contrasts nicely with trillium. Look for red-foliaged epimediums, Japanese painted fern, and fern-leaf bleeding hearts. You can also plant trilliums in among evergreen ground covers, such as vinca and ivy. The colorful flowers will bloom above the ground cover foliage in spring.
Trillium spreads by clumping and self-sowing. However, it's not easy to germinate trillium seed. It's best to purchase nursery propagated and grown plants. Seed grown plants can take up to 10 years to bloom.
Small trillium plants bought online or at the local garden center should bloom in a few years. As clumps spread and more flowers are produced, it might be tempting to use the trillium flowers as a cut flower indoors.
While this won't kill the plant, it will reduce flowering in subsequent years because you're most likely removing the leaves as well. The leaves only have a few weeks to store energy in the roots for next year's bloom cycle.
Since trillium plants go dormant and disappear by midsummer, mark where you'll want to plant more trillium in fall or early spring in the forest or your shade garden. The last thing you want to do is dig up established clumps because you didn't know they were there.