When you say montbretia, do you mean the wild form of Crocosmia, the basic C. masonorum, or are you talking about one of the more modern hybrids?

Thin them out - they do stop flowering when too congested. Bin the old ones as if they are the old variety they are invasive and must be kept out of the wild.

Thank you both. It is the common Crocosmia and will dig it up and thin it out and hope for better results next year.