From what I have read they are cold hardy to zone 3 so leaving it out should not be a problem. I am in zone 4 and planted one this year and expect it to come up next year. Mine has about 4-5 stalks just starting to open now.

I divided one this spring, that would have had more than fifteen stalks. And it doesn't get any protection, is in a low spot by a downspout. I make sure the crowns aren't covered. Others survived on a slope, with better drainage. Why are you so doubtful that your well-drained cardinal flowers won't survive in zone 6? People in zone 4 have cardinal flowers. Bringing in a plant that's used to winter dormancy might not be good for it at all.

Leave them be just don't cover them up in the winter and don't pull them in the spring thinking they are dandelions which I have done. They like lots of moisture they will spread I think by seed too because mine are scattered all over the place and I know I didn't put them there. Sarah

kept hearing from people that it wasn't that hardy and that significant winter protection was HIGHLY recommended.
if everyone is having success outside, that's reassuring. i will just leave it outside

thanks

Mine was just starting to really grow. It is about 6-8 inches tall. Today, or last night, something bit the top off about three of the plants. What could have done this. The tops are missing, so it must have eaten them.

Oubliette, I also have tried several attempts at growing this hummer magnet. Down here in the deep south, there is some kind of moth or skipper that lays eggs on this particular plant. At this time of year the eggs have hatched and the fast growing worms or caterpillars have reached a size that the plant is devoured almost overnight. They are unnoticable and small at first as their color is almost the same as the plant. They grow fast and quickly make a salad out of all of your plants.
I don't know if this is the cause of your problem but I would suggest a close examination of your plants as soon as possible. I have never had any cardinal flowers to get large enough to bloom as they were eaten before it could happen. Insecticides are not what I wanted to feed my hummers and the worms were too numerous to pick off.

That's a shame up here we have japanese beetles and big green june beetles in july that eat everything in sight so everyday I try to catch and kill as many as I can they have eaten some of my cardinal flowers too! but the june beetles have eaten a good bit of my salvia guaranitica's Sarah

Thanks, Jim. I will check this out today. It did look as if it could have been worm damage. I really hate to hear this. These were from seeds that Penny sent me and I have been caring for these plants since March. Because I couldn't find a spot that seemed to provide enough moisture, they were in pots on the deck so they could get a good watering every day.

This is one plant that I do not have but just saw some at LOWES"---they are quite large plants there and I was temped to purchase one but was not sure where to put-----the tag said shade and they were in full sun at LOWES"--------what do they need sun or shade????----thanks---ED

Mine are in sun they like moisture. I had some in true shade several years ago . They didn't do as well. Sarah

I have one with dark red, almost purple leaves, and one with bright green leaves. they were tagged the same, lobelia cardinalis. are they both really lobelia? which kind is preferable? thanks.

My cardinal flowers survive the winter just fine. I do have problems with the deer eating the tops off of them. They do have a tendency to wilt the year I plant them, but after the first year they are pretty hardy. They usually last about 3 or 4 years.

Richard

I think the dark leaved ones are the mexican kind or a hybrid of cardinalis and splendens. it's not as hardy. Sarah

I've had sawfly larva play hell with some plants - one rose especially, native azaleas , and blue Stocking Monarda. they might be your worms. Bt doesn't work on them but insecticidal soap should. Hand squashing or simply flinging them into the grass to meet their fate also works if you get them soon enough. and I heard wrens can do the job - my rose had no problems the year I had a wren house near it. so that's going back next year.