I have a few buddlejas in my very small garden but, I have to say, the butterflies are not particularly attracted to them. They much prefer smaller-flowered salvias and verbenas. I presume the one you photographed earlier in the thread is
'Black Knight'? I took a cutting from my sister's last autumn and it struck. Although only one stem of about a foot long, it sent out a flower head which I let grow and die off. Time to plant it out, I thought and decided which tub it was going in. I then promptly snapped it! The air was as blue as the flower but every cloud has a silver lining. It has sent out 2 or 3 new shoots from the base.