I had groups of blue, white and yellow irises mixed together, but now there seems to be only blue ones in those positions. The few yellows or whites I see are alone. Do the blues kill off the opposition ( I’m told the European bluebell does this to the native Irish one by secreting a toxin into the ground – is this true?), or are they just better at surviving/longer lived?
The blue kinds do not kill the opposition, but plants with more vigour survive better. In the case of Spanish bluebell, there is some evidence that it is hybridizing with the native kind and thus diluting its genetic purity, but not poisoning it.