Eupatorium purpureum: seeds

Eupatorium purpureum, known in English as sweet Joe Pye weed and in French as eupatoire pourpre is a perennial native to eastern and central North America, bearing fluffy umbels of pink-mauve flowers.

This is my first time growing Joe Pye weed. I bought these seeds from the North American Native Plant Society at Seedy Saturday. I am cold-moist stratifying them in the fridge to simulate a North American winter.