When I first started researching plants for bees in 2010, solidago - Golden Rod - was a plant I found included on several lists recommending plants for bees. Based on this I tried two species - canadiensis and virgaurea. Both produced quite disappointing results attracting flies, beetles and hoverflies but only a very occasional bee. However, once you have planted a patch its easier to leave it than to dig it out and so the canadiensis has stayed in the research bed, ever since, attracting the same range of non-bee pollinators and I removed it from my sales range.
Then this year, one very warm week in mid-August, I found bees on the plant - not just one but several - honey bees and two different solitary bees. And I found them there daily for about a week. Then the plant began to 'go over' and the bees naturally stopped visiting.
So this leaves me with a dilemma when recommending plants. Do I include solidago, which for one week in five years attracted around 10 bees per square meter making it a medium high attractor....but just for one week? I think that the only solution is to ask others to let me know if they get bees on their golden rod and if possible how many. Emails on the subject very welcome