I read that they are invasive. How do they spread, and just how invasive are they? Are they the type of invasive plant (and yes, I know invasive can mean different things to different people/situations) that can be kept in check easily?

I have also read they need constant moisture. How true is this? Do they die if not given enough moisture, or just wilt until given extra water? Does the foliage scorch in too much sun?

I love the look of these plants. The bigger species/cultivars are amazing, though I certainly don't have the room for them. There is one kind, P. frigidas var. palmatus 'Golden Palms' that is a bit smaller at 2ft tall 4ft wide. It is z6-9, but it looks like something I might be able to get away with a little zone pushing.
I don't know if I will ever be able to get a Petasites, but I would love to know more about them anyhow.
Thanks!
CMK

Hope that helps. My advice is: Proceed with caution. I've heard the variegated one is less aggressive, but can't confirm that.

They are pretty things, but I think I might pass on them. I have learned my lesson when it comes to planting possibly invasive plants, especially in a garden with limited space.

Oh, I love the look of bog gardens! What did you replace the Petasites with?
CMK

There are other large-leaved plants that I'd love to try growing here in my new garden, many of them also like boggy conditions, but are less aggressive spreaders than Petasites. I don't know if you're familiar with them, but here's a list of plants I'm planning to try, if I can get my hands on them. I think a couple of them are hardy in your zone.

Astilboides tabularis
Darmera peltata
Gunnera manicata

The Petasites did give the area they were planted in a very lush, tropical look, but it wasn't worth the headache they posed.

-dawiff, great looking list! I am familiar with them (though I have only seen the Darmera once before...). My ex-neighbor used to grow Astilboides. Really interesting plant. But hers stayed small and only had a few leaves because she moved it around so frequently.
You must have a lot of room in your new garden to grow a Gunnera! Those get about 12ft or more around in time don't they? Your garden will really look stunning with all of those big foliage plants.

Have you ever tried an Ornamental Rhubarb? One, Rheum palmatum 'Atropurpureum' is really awesome. I just have a regular old rhubarb, but I do love the foliage.
CMK

Darmera is native to this side of the Cascades. There is a large patch of it growing naturally in the ditch just up the road from me. The best part is how it looks in early spring when it blooms, before the leaves emerge. But I don't think I'd want to have it in my garden unless I had a LOT of space.

Never knew Darmera was native. I have never seen them before when I was over your way, though then again I have never taken rambles deep into the blackberry patches in search of it ;-)

I think I might end up going with a Rodgersia or Syneilesis aconitifolia. They are not too big but still have interesting foliage.
CMK

Not a big fan of Ligularia. The soil over here dries out too fast for them.
CMK

Again, as mentioned previously, they did receive some supplemental irrigation. I would give them more shade if irrigation was minimal or not possible. Mind you, WA in May or June is likely very different than ON!

I planted Astilboides, darmera and petasites three years ago in an area that gets about 4/5 hours of full sun and where the soil stays on the moist (read NOT wet) side. I love the Astilboides and the Darmera. I hit the petasites with roundup last year when it started popping up in my lawn. The main plant is gone, but I'm still battling them coming up elsewhere in the yard.

Alexis