I have a lovely pure white one that grows out of the side of a step. It has never spread😕 The pink ones aren't great spreaders either. The blue ones are a pretty PITA.
Just don't let them seed. I've given up trying to dig them out. My arms aren't long enough for some of them! I slice them off at ground level and forget about them until next year ad infinitum
You can either snap off the flowers as they fade (ie before they produce seed) and leave the leaves and bulbs, if you want them to appear again next year. (The bulbs can also replicate underground so you are likely to get more even if you remove the flowers.) If you don't want them, dig the entire plant up, with the bulb - that's the best way of getting rid of them, again as the flowers fade. You may want to allow a small area to continue, like I do in my garden, and clear the rest. As some others have said, they can remain quite controlled sometimes but invasive in other situations. It depends on whether your soil and conditions are to their liking!
I haven’t had time to smell the bluebells, but they are easy to pull from the flower stalks so preventing seeds should be easy that way. I think the leaves are harder to pull off.
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The pink ones aren't great spreaders either. The blue ones are a pretty PITA.
This is a wild bluebell in the wood at the side of me, see the difference @Voyagerxp .