Most books and catalogues do class them as zone 4, but I grow a few here in zone 2b.
You just have to find a perfect spot for them. The soil should be fertile, humus compost rich, moist and well drained. They also like mulch around the plant to keep the roots cool and moist. They absolutely do not like hot windy dry sites, brown, curled leaf tips are a sure sign that plants are unhappy with their site.

It's also a good idea to make sure to cover with loose straw around freeze up time just in case you don't get any snow.

Astilbe 'Bella' is a arendsii hybrid.

Sharon

Dominion Seed House also has seed, just titled 'astilbe mixture' and they list the seeds, as well as any rooted astilbe plants that they sell as hardy to zone 4.

I had a few plants, north side of the house, that survived a few years before dieing out, but my conditions were anything but ideal (the part shade, moisture, and good snowcover were good, the heavy clay soil wasn't).

My Mom had astilbe growing at the lake, zone 2b, on the east side of the house for a few years as well, but if I recall correctly it died out after she moved it to a colder spot in the yard.

To me it sort of behaves like a zone 4 perennial in our zone, surviving in an ideal location, or with good snowcover. There is an astilbe in Dominion's catalogue named 'ostrich plume' that I was debating on getting.

Ironically, however, Dominion lists astilbe as zone 4 and hardy hibiscus syriacus, the large flowered ones, as zone 4 as well. I've tried both and astilbe seems to survive a few winters, hibiscus not at all, so maybe their zone ratings are a bit out of whack, at least with regards to hibiscus.

Glen

Thanks for the info Sharon & Glen. I ordered the seeds anyway. I need as many part shade choices as I can get now. I keep seeing it listed as a "full sun" plant, I guess that depends how hot and dry your sun is. Glen, interesting about the hibiscus... ah don't we wish.

Astilbes do about the same for me here too. I've had 2 plants for probably about 6 or 7 years, but they don't get very big. They tend to only bloom, usually only stock, in wet years too.

Why don't you try Aruncus dioicus or goatsbeard? It's ideal in part shade, and it looks like a huge astilbe. I've had one for at least 7 years, and it's close to 5 feet tall and 3 feet wide and it's a mass of blooms come summer. Last year I picked up another one for my "troubled" shade bed, hoping it'll do as well in there. I picked it up at Canadian Tire I think for $2 or $3. It was a small pot, probably 3", but they grow quickly.

If you're looking for part shade seed, I've got some hosta seed, 'Elegans' and 'Frances William', and some ligularia seed if you'd like to give them a go. Just let me know.

I have two kinds of Astilbe for years. One is a tall variety and the other low growing and spreading. I have them at the end of my front foundation bed. These two have been very reliable.....especially in a spot where not much else will grow. They are about 3 feet from the foundation, so really are not protected that much by it. They get sun in the morning till about noon.

Sierra

Laurie, Aruncus is beautiful and I plan to get some too, but I wanted Astilbe for the red and pink options. Also, even if it doesn't bloom it has nice leaves. And I would absolutely die for some ligularia and hosta seeds, oh yes please yes please :0D LOL (only if you're not going to use them) I will e-mail you.

Sierra, wow I wish I knew what kind you have, I would get that because you have colder winters than me. I think. Mine will be getting morning sun too.

Thanks again for the ideas.

Gillian, I have some Primula cortusoides seed which is a good part shade candidate (see the first garden photo in the bubble thread - pink/lavender blooms). They're easy from seed. Email me if you're interested.

Gil, I just got back from Wal-Mart and noticed that McKenzie seeds sell A. arendsii hybrid seed for only $1.69.

Thanks Sharon, McKenzie's the brand I grew last year and had a few seeds left. I bought the one from Stokes too. Took forever to germinate last year, I already started the ones I had left. So I guess I will have two different x Arendsii hybrids. They're probably the same thing. LOL.

northspruce, I've had several astilbes for years, none hybrid: light pink, medium pink, dark pink, white, and almost red. Some are tall, some medium. I've never lost a one. Maybe they're hardier than the hybrids? Mine are in part sun, well drained rich compost, mulched for winter with Oak leaves and pine needles. I've traded all the seed except for some medium pink, which you're welcome to. Send me your addy and they're yours.

I do have one hybrid, the 'Amethyst', which is in its 3rd season and doing well. It's in a protected location.

Constance.

Did you start 'Amethyst' from seed? I've coveted that one for awhile, but hesitated because of the iffy zone ratings. My astilbes are in part sun as well (late afternoon). I've only had them since the fall of 2005, so they aren't really tested well with last winter being so mild.

Constance, thanks so much for the offer, but I have two packs of seeds on the go now, I don't think I have room to start any more right away. If I have trouble with these not being hardy, I will certainly try the species like you have.

Gillian