Bluebells

I dig bluebells out of the flower borders, they were taking over but some are allowed in grass under a silver birch at the front. I'm always torn at this time of year, whether to let the volunteers flower before attacking them.
If you have grape hyacinths in your woodland patch I can't understand why you would have room for bluebells suck it and see, try putting the different colours in first. How about sinking a container of bluebells in an effort to restrict them, like we do with mint.