Herbaceous Perennial Plants
When you receive your order, open the bags and check the stock. Roots and crowns should be firm and pliable. If they are slightly dry, add a little water or, if they are going to be potted up soon, wet the roots. Generally, a little surface mold is harmless and will not affect the plant’s future performance. If you cannot pot them up immediately, store them in a cool (35–40°) location for a short time.
Do not plant bare-root perennial plant crowns directly outdoors.
Pot up the rootstock using well-drained potting mix in a deep 6" pot or a 1-gallon container. Avoid coiling the roots in under-sized containers.
Grow newly potted perennials for a few weeks in a protected location in indirect light at 50–60°. Wet and/or cold conditions for an extended period may cause rotting.
Transplant outside once they show some top growth and the danger of frost has passed.
For more info:
About planting bare-root perennials.