The dust like things are the seeds.
From the link:"Seed - sow spring in a greenhouse and only just cover the seed. The seed usually germinates in 1 - 3 months at 10°c. When they are large enough to handle, prick the seedlings out into individual pots and grow them on in the greenhouse for their first winter. Plant them out into their permanent positions in late spring or early summer, after the last expected frosts."

BTW, my seedlings didn't survive as I didn't winter them over in a greenhouse.

Here is a link that might be useful: More info