Dividing & Transplanting: Trillium don't like to be disturbed and can be hard to divide and transplant successfully, especially from your forest. However, it can be done. In your shade garden, you can dig and divide your own trilliums. Mark where your trillium are growing in the spring.
In late summer, after they go dormant, carefully dig the rhizomes, getting as much of the root system as you can. Gently separate out the individual rhizomes and replant in a location similar to where they were growing well. Keep watered, especially if you have dry conditions.
Digging trilliums you planted in your own forest is harder and less successful because the rhizomes often are growing in among tree roots and other plants. Removing the whole root system without significant damage can be difficult.
Pests/ Disease: Trilliums have few pests and diseases. In the shade garden, watch for slugs and snail damage on the leaves in spring. To reduce damage, remove the mulch away from the plants in spring to reduce hiding places for the slugs.
If possible, avoid killing snails and slugs, because they're helpful in building nitrogen-rich, mineral-laden fertilizer that enhances plant nutrition. To eliminate slugs and snails, you can also use beer traps. Sink a shallow bowl in the soil, so that the rim is positioned at the soil line. Fill it 3/4rds with beer. Each evening the slugs and snails will drown trying to drink the beer. Clean out the bowl each morning. Keep your dogs away from the beer trap because they might like to taste it too.
In the forest, deer may browse on the plants, but usually this damage doesn't kill the plants. If you have a special species you're trying to protect or a new planting, cover it with chicken wire in spring after it emerges.