I plant when when the next door neighbor's lawn turns yellow with dandelions. Probably in the next week or two here in SW Denver.

That sounds sensible. A phenological guide.

Here are two guides in Colorado:

GHOrganics, phenology and

Colorado State University, soil temperature.

By the way, if it bugs you that CSU refers repeatedly to "table 2" and yet, there is no table 2 ... do a search of the University of New Hampshire's website. You will find the same article and table, with no reference to a #2!

I must have used the dandelion indicator since I planted the seed potatoes a week ago when I saw the first blooms. But, didn't measure soil temperature until today.

Steve