Just to be on the safe side, I would stake them. I have never seen them get that big before either, but hooray. Sounds like they will have lots of blooms. It's one of my favorite perennials. Such an incredible RED.

I agree it would be safer to stake them. I haven't had this experience with cardinal flower, but I've seen other wildflowers grow to enormous proportions in garden soil. 6' calico asters and 5' northern sea oats come to mind. In the case of lobelia, I think it's a good thing.

DG, I have grown Lobelia cardinalis and seen a great deal wild (which is breathtaking). I have never seen it topple, ever.

However, the wild stuff took seed naturally, and the planted ones were in stable soils. So what do I know? :)

So very red!

Did not get them staked too soon! Had a few less-than-optimal bamboo remnants from another project and rather haphazardly propped up the tallest plants ahead of an expected storm front. When I went out afterwards I found the SHORTEST plant, one I had suspected would not be at greatest risk of "toppleage" had indeed doubled over, but the stalk was not yet fully crimped. I was lucky and got er upright AND STAKED before the damage was irreversible.
I decided to make good use of an unloved phragmites patch over at my mom and dad's and now have more canes drying than I really need. WHen you need some garden stakes and the stuff you're using is invasive anyway, it's hard to stop cutting! I find that good wooden clothespins do a fair job of keeping things anchored to the supports...don't clamp the stems to the canes, rather, use the open end to keep it there, one on each side. THese can be adjusted easily as the plant grows, too.
THe tallest lobelia is now about 6'3 or so, and has shoots coming off every few inches on the stem where I can expect more blooms. I used to think nothing was as red as cannas but I am totally blown away by these beauties. Has to be because of the constant downpours we have had this summer, along with the composted muclch in that bed. The tall bellflower is beyond belief as well, there is just blue everywhere, and it just happened, I did not plant it.

thanks for the replies, everybody.

but, but, but...pictures? Please?

Its pretty common for wildflowers to grow enormous when planted in a garden... where soil has been amended and competition has been reduced.

Joepye...funny thing! I am sitting and admiring my area of joepye weed I set out last year and was thinking about what you said concerning wildflowers doing so well in a "garden" environment. The lobelias are still going for the sky, the joepye is almost through blooming at about 6-7 feet tall and this is only their first full year since most things got set out last summer. One thing does have me puzzled though. I also set out some eupatorium coelestinum-some say conoclinium- (blue mist) and they self-seeded as expected last fall. Trouble is, they are not performing like everything else, in fact I just caved in and offered them a touch of miracle-gro because I was afraid they would conk out altogether. They look as if they were burnt, some are totally dead, as if there was not enough water or they were blighted or something. Perhaps I should have thinned them, but I have seen them is dense clusters naturally and they looked fine.
That should have been one of the easiest things to grow and already my brown thumb is sticking out.