I grow 'Wild Cat', a big sprawling thing that I'm very fond of, though it might not be to everyone's taste. I've also grown "Little Trudy', which has proven not to be very much, at least in my garden.

I have N. subsessilis and the shorter variety 'Blue Dreams' in my garden -- love them. The pink forms 'Pink Dreams' and Sweet Dreams' are also cool.

I also have subsessilis. Love it, as do the hummingbirds and bees. Goldfinches swarm over it for the seeds. It reblooms sporadically if deadheaded. It is tall, about 4 ft. Sturdy, does not flop.

Here is a pic for you taken this summer. It has been with me for 5 years. 3 plants in this spot.
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N.sibirica has a running habit. N.clarkei lacks vigour. N. subsessilis is a clumper,has to be watched carefully for selfseeding, the foliage smells unpleasantly for my nose. It is robust for me. Ornamental value is average to below average , the flowers should be bluer in my opinion, and there should be more of them.