Outstanding perennials (1999):
Notable perennials (Summary from Allan Armitage talk, 1999).

Growth Regulators:
Growth regulators for containerized herbaceous perennial plants (Growertalks, 2020-2021).

Clematis:
Plant evaluation notes:  Clematis for Northern landscapes (Hawke, 1997).
Clematis (Iowa Extension Service, 2013).
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