The message from Hettie® contains these words:
The nyger seed sold for goldfinches, is a tropical thistle from Africa. It's not the same plant as the Scottish thistle, at least, it won't germinate here in Scotland :-)
For some weird reason, birds are very fussy about where they eat nyger seed from. For a long time I tried in vain to tempt goldfinches with niger seed, which I put in conventional seed holders, or on the bird table. Every bird in the garden refused to touch it and many other gardeners I know, had the same experience.
Then at a friends house, I was astonished to see a dozen or more goldficnches flocking to a special nyger-seed holder which is a plastic tube with very narrow holes at each feeding-station. I bought one at Petsmart, and now we have flocks of goldfinches. They still won't touch nyger seed served any other way.
Janet.