Herbaceous Perennial Plants
When you receive your order, open the bags and check the stock immediately. Roots and crowns should be firm and pliable. Surface mold is harmless and will not affect the plant’s future performance. Store plants in their packaging in a cool (35–40°) location until you are ready to plant. If it’s going to be awhile, you can pot up your perennials.
Do not plant bare-root perennial plant crowns directly outdoors before danger of frost has passed. Wet and/or cold conditions for an extended period may cause rotting.
For more info:
About planting bare-root perennials.