| Trilliums grow naturally in cool, moist, humus rich soil in shady forests. Your area for them has too much sun; the raspberries may be providing some shade but the area is likely too hot and too dry for trilliums. Trillium will go dormant and disappear especially in dry conditions. They grow slowly, taking about 10 years from seed to get to blooming size. See below for more details. |
Here is a link that might be useful: Trillium growing tips