I want some tall, dark blue violet spikes that grow well but are not highly invasive. Any suggestions? There are so many varieties I don't know where to begin!

Are you tied to bellflowers or are you willing to look at others?

All suggestions welcome!

Not sure what zone you are in, but for dark blue violet you can't beat May Night sage/salvia. Bellflowers are notoriously invasive. I have been digging out creeping bellflowers on my corner for about 10 years and they still keep coming. The only tall bellflower I would recommend is Sarastro, and that isn't spiky...it has big purple bells. Some of the Veronica spicata cultivars might work also. If you want REALLY tall, like 4-6 feet, go for delphinium.
There might be more, but that's what I can think of for now.

Thanks! I did have salvia may night but it doesn't seem to be very tall any more. How does the invasive bell flower propagate? Running rhizomes? Seeds? I have some Penstemon Mystica which self sows like crazy, but it is really pretty and I just dig it up wherever I don't want it. I am in zone 4B.

Bellflower has running rhizomes. They can go really deep... so you keep thinking you dug them all up, but there are always more. There's no way you can dig them up and actually get rid of them. I have Dark Towers penstemon which is similar to Mystica - I love it. I usually cut the stalks once it is done blooming, so I haven't had any issue with it self-sowing. I wouldn't mind if it did!
Another campanula you could try would be nettle-leaved bellflower 'Bernice'. That again has bell-shaped leaves but gives somewhat of a vertical effect. I have posted some photos of it on this site. Still, none of these have the deep color of May Night, and the bellflowers would not either. They are usually a lighter shade..
There might be newer cultivars of the salvia that are taller than May Night. Madeline or Caradonna maybe? I haven't looked lately.

foraygardengirl said:Bellflower has running rhizomes...

For the record, "bellflower" is the common name for the genus Campanula which has over 300 species and most don't have running rhizomes... just pointing out that this is not an accurate generalization. The genus contains a lot of excellent garden plants and should not be condemned on the basis of a couple of invasive, though unfortunately commonly-grown, ones.

Lori,
You are entirely correct. I do not know details of every kind of campanula, certainly, but in my experience, the tall varieties of which I am aware are invasive with a couple of exceptions.

I suppose maybe a google search would be in order at this point?

Caitlin - absolutely, I would research the heck out of this subject before planting. However, I highly recommend you don't plant campanula rapunculoides, which is the one I have been trying to dig out of my garden for years.

foraygardengirl said:However, I highly recommend you don't plant campanula rapunculoides, which is the one I have been trying to dig out of my garden for years.

Absolutely! This is, in particular, the one campanula that could give the innocent others a bad name! This is one of the worst weeds in North America and no one should ever intentionally plant it... yet I used to participate in a forum where people happily passed it around, despite the warnings... brrr!!!

I ordered a Campanula Persicifolia and also an Adenorpha from Bluestone to plant this fall. They are not the most invasive, according to various snippets I read here and there on google.

Perscifolia will spread quite a bit but should be okay. Be aware it is slug candy...they love campanula. The other one makes me very nervous because it looks identical to rapunculoides...

Thank you for the caution! I can always contain it if it gets too rowdy.