I have some Primulas I would like to propagate, specifically Primula elatior and Primula veris. What is the best method, and when is the best time?
The timing will depend on the propagation method you choose. The American Horticultural Society’s Plant Propagation (edited by Alan Toogood; DK Publishing, 1999)says that division is done in early spring or after flowering; however, this method is not recommended for any species except Primula vulgaris and Polyanthus primroses. Although division is a healthy practice for some species, it can weaken others.
You can raise your primroses from seed, which has the benefit of being a virus-free propagation method. This is done in either mid-spring or in late summer to fall(the later time period is rated as easier than the earlier). However, Primula elatior, Primula veris, Primula vulgaris, and candelabra-type primroses may hybridize if you do not isolate them. Depending on your outlook, this could be a problem or an opportunity. The seeds are best sown when fresh, in a well-drained, moist soil mix rich in organic content.
There is some propagation information in this Alaska Master Gardeners article by Mary Jo Burns, entitled Growing Primula in South-Central Alaska. You may want to see if your area has a chapter of the American Primrose Society. Members of the Society have access to informative articles about all aspects of primrose cultivation.