July 2005 issue of the Cornell Flower Bulb Research Program Research Newsletter:
While considering problems with regrowth of perennials, we conducted several experiments looking at planting depth of the bare root. Commercial recommendations often state “plant the crown 1 to 1-1/2 inches (3 to 5 cm) deep”. Our results very clearly show that such planting depths are almost always bad for regrowth. When the crown is planted so the buds are at or slightly above the soil line, superior growth results.
Read the whole article – Starts on page 3.