My understanding is that only American or a Canadian plum can pollinate Pembina. Do you have a patch of native land close by or someone else that may have one or the other?

In the past many nurseries promoted nanking cherry as a pollinator of hybrid plums. If they both bloom at the same time I believe it will work. In my experience most years nanking cherry blooms before Pembina and only a small amount of overlap occurs. Most sources now promote using a native plum to pollinate the hybrid plums. As Wayne says that would be a Canadian or a American plum. The native plums are slow growing so you may want to hang onto the nanking cherry till you have a native plum with flowers on it.

It’s a myth about Nankings being a pollinator for plums.