Do not purchase over the Internet, especially bareroot unless you have ordered previously. Get your plants locally and remember astibles like moisture and filtered sun so amend your soil accordingly.

Here is a link that might be useful: Propagating Perennials

I've found that bareroot astilbe put up nice foliage the first year (and on some, I had one small plume), and then they began to fill the in second (maybe 3 plumes), and come up to a nice size by year 3. Since many garden centers start selling bareroots now, while our ground is still frozen (Z5), I pot them up in late March, only water them when I see some shoots, and let the roots develop well in the pot until late May, even June. This helps me keep an eye on them until they come up to a better size to transplant. They do take a bit of care in this stage, though.

This technique is suggested in The Well-Tended Perennial Garden.

I second the recommendation to get them locally. I got a couple of plants from my MIL and they transplanted great. They may not look the best at the nursery but once they get put the ground they will perk up I bet.