Mayo62 said:I didn't have any rust this year 
Hopefully that means there are no spores in my plants 
You would have to have daylily rust spores floating around in the air in your garden for your plants to get rust. That's not likely where you live unless you have other daylily growers with rust nearby or you already have it. Did you have rust last year?
Mayo62 said:
Is it clear what combo of temps / rainfall (or moment of watering?) / humidity trigger rust?
Perhaps my summers are just not hot enough to get rust? 
Very hot weather discourages rust but if you don't have the spores in your garden then there's no way the plants could get rust anyway. I don't know what the current status of daylily rust is in the Netherlands, do you know of anyone with daylily rust there this year?
For an outline of the environmental conditions required for daylily rust, see the second question and answer on my rust site's FAQ page here:
http://web.ncf.ca/ah748/FAQ.ht...
If you want to get into it even more deeply, there is a link at the bottom of the FAQ page to the full research paper from which this information was taken.
