Never grown them from seedlings but they root very readily from softwood cuttings. You can grow them by the dozens that way. Use a somewhat gritty mix.

Thanks for the response, I have rooted a couple (don't tell the patent police!) and really like them, but I was just wondering if the seedlings will offer up any kind of range.

I weeded today and found a couple green seedlings too. Maybe I'll start a ninebark patch and see how they all turn out. Apparently coppertina is a cross of Diablo and Darts Gold so I suppose in theory I could get anything in between.

Yes, that is the cross for 'Mindia' (Coppertina). I've already gotten in trouble on here for alluding to growing patented plants from cuttings! I have never sold or even given away one. I propagate for Master Gardener sales and we are very careful to check patents and trademarks. Have fun!