Not an expert but I have tried several times different sea hollys and have never had them return the second year. The last one I brought I paid 15 bucks from Garden Crossings. So a lot of wasted money for me.

If I had to choose I would go for the Thistle because that survives for me.

I highly recommend the inclusion of a "Sea Holly" or two in any perennial garden. Its texture and colour are incredibly unique and they are butterfly magnets. I have several varieties in my gardens. I believe both plants shown below are Big Blue from this past summer (I hope you can see the monarch butterfly in the second picture). I have not yet had any issue getting any of my "Holly" surviving my Z5 winter. Once established they thrive in my hot dry clay soil. They are outstanding perennials.

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Wow, thanks for sharing those pictures; I esp.love the swallowtail butterfly pic. Now I'm thinking that I don't have enough sun for the sea holly, but I sure love that blue!

prairiegirlz5, I know this plant calls for full sun but mine receive for sure less than 6 hours and do just fine. Do an experiment and try one to see how it does.

Neither I'm afraid. Lol! I haven't been able to grow Eryngium well at all. My 'Jade Frost' was a terribly tipsy (these can flop even more if the soil is rich) plant that needed staking while in bloom. Think it might have rotted out this year, not sure. Eryngium have long tap roots that, in my experience, do not transplant well (learned the hard way, RIP E. 'Blue Hobbit' LOL!).

Echinops has been a nightmare for me. It reseeds profusely and the seedlings are difficult to dig out, what with the long and brittle tap root. To prevent reseeding you have to deadhead immediately after the blue flowers fade. If you don't get them right away and go to cut later you will find the seedheads shatter easily, dropping their seeds anyway.
To make matters worse for me, my skin gets VERY irritated from the prickly foliage of this plant! Last spring I decided to finally get rid of my big 'Blue Glow' Echinops, so dug it out and chucked it. When I checked the spot later in fall I was dismayed to discover the thing had come back. Appearnatly, leaving any amount of the roots will result in it re-growing :-(
Another negative of this plant is that the bottom foliage can be ratty looking and yellow a bit even before bloom.

If you still want to go with one of the two plants I would probably say go with the Sea holly. At least that one isn't a pesky reseeder! Who knows, maybe you will even get lucky and end up with plants as nice and happy looking as Rouges ;-)
CMK

christinmk wrote: My 'Jade Frost' was a terribly tipsy (these can flop even more if the soil is rich) plant that needed staking while in bloom.

That was experience also with "Jade Frost" and with "Blue Glitter". One option is to surrounds closely either of these plants with other tall perennials for natural support. Otherwise dont select these particular varieties. "Big Blue" is for sure self-supporting as seen in the pictures above.

I'm with Christin--neither. I've heard nothing but negatives about globe thistle reseeding and the sea holly I bought from Bluestone, planted in full sun and watched for three years got shovel-pruned in 2010. It never grew more than about 18 inches tall, bloomed early then the whole plant looked brown & ratty the rest of the season. I never did see a butterfly go near it.

I planted balloon flower in its former spot so I get the blue color but without the ugly, dead-looking, prickly foliage. Balloon flower blooms late in the season too and in my experience has a longer bloom period. I brought the balloon flower with me from where I lived previously so the plant is 10 or 12 years old by now. Other than whacking it back to about 10 inches the end of May (so it doesn't flop), I do nothing else to it the whole season except harvest seeds in the fall.

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I'm with rouge21 on this, although my Eryngium planum 'Blaukappe' does fall over if not staked or otherwise supported and it will reseed. That said, I would not be without them. Every size and shape of nectar lover comes to it. Bees of all sorts, butterflies, you name it. They too get about 6 hours of direct sun. One other caveat is the smell of the blooms. Best described as, well, a marathon runners socks..in august.

tj

Here is a link that might be useful: Blue Cap

EVERY PLANT reseeds if given a chance(unless sterile). This is the meaning of flowering: to attract pollinators and setting seeds. It is actually very easy to remove spent flowers if taken simple precautions. I have both echinops and eryngiums and I cannot recognize the HORROR stories at all. Yes, echinops can regrow if dug up, but so do phloxes, papavers, eryngiums and many others with long deep roots. But it takes time for the seedling to make a root deep enough to regrow, so digging to China is a bit of a stretch in my opinion. My advice is : if you like the look of them , plant them and enjoy their beauty, just taking care of preventing reseeding in good time. Out of eryngiums, I found E.alpinum to be the most ornamental, but not particularly long lived in wet winters. Out of Echinops, E. ruthenicus is hard to beat(EVERYTHING is ornamental on this plant)

For me eryngium is super easy to grow. It also reseeds a bit too much, but not wild crazy. They have a beautiful steely color that is quite striking.

HOWEVER . . . it STINKS! Horrible! Every time I pass it I think "Whoa, did I just step in some cat poop?" and then realize I have passed the sea holly. So I have been ripping it out of all beds except the one that is viewed from a distance. Too bad, it's so pretty and easy. Will mail plants for postage if anyone wants them.

Sure is pretty though :-) Here it is with echinacea and phlox in the background, so they have a nice overlapping bloom time.
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gottagarden that is beautiful. I wish they would grow in my garden.

-wieslaw, yes, but a plant may be passive in one location of the globe and a pest or even invasive in another. I don't feel I exaggerated in the least. I'm simply reviewing my findings in my little part of the world and my experience has found Echinops to be pesky devil, lol. ;-) Perhaps the seedlings are easy to extricate in some soils, but in my rather hard packed tough soil they certainly aren't!
Anyway, forewarned is forearmed and at least folks can know it does have the potential to become an annoyance...

-Brenda, fantastic! What a gorgeous grouping. What variety of Eryngium is that? Is that 'Vera Jameson' Sedum at his feet? Lol! I had no clue they smelled so much like cat poop! I do have a couple plants that smell like skunk though. In the early days of their residence here (when I didn't know it was them making the stench) I really thought that a skunk must be living (or dying) around here! Lol.
CMK

Don't remember which eryngium, I've had them for many years. The sedum is Bertram Anderson, much darker than Vera.

Skunks smell nicer than this plant :-0

Well, seeing that spectacular photo made me think I might want to rethink eryngium but then I read about the skunk smell and will therefore happily stand behind my original instinct to shovel-prune my original plant. Balloon flowers have no scent, pleasant or otherwise. Stokesia 'Klaus Jelitto' is another no-care/no problem late summer bloomer with blue flowers that adds a bit of (soft) spikey texture to the perennial border. I'm new to lobellia siphilitica so can't say how it behaves yet but the blue color (and lack of scent) have me hoping it doesn't become a problem since the bees love it.

Winter sown Lobelia siphilitica/Great blue lobelia
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Thanks to everyone that replied and esp. to those who shared photos. I know I want the phlox and the lilies are on order, so maybe that will satisfy my need for "new". I'm very sensitive to smells, that rules out the sea holly. How could I forget I have Rozanne geranium too? I was "planning" (more like I was thinking of) edging both sides of a grassy path between two sides of the yard with the geraniums and the calamint, with lady's mantle and the daylilies in the middle of one side, with ageratum to spread the blue and contrast with the peachy daylily color. The coneflowers, phlox,lilies and agastache should be plenty to start with. I also forgot I have a blackberry lily that could be tucked in. I do like the balloon flower, a lot, hmmm...

I just saw Eryngium big blue and am tempted to get it based on these pics. How tall does it get for you folks? I have a spot with great drainage just for it.

I have had Echinops 'Veitch's Blue' for a few years. I cut some flowers for inside the house and deadhead faded flowers, though not necessarily right after the flowers fade. I have never had a problem with self-seeding.