I've been trying to apply them directly to what grows in my own garden.
For instance, though the connection is not made on the website I provided, last year, my seed potatoes came with instructions to plant at a certain soil temp. As it turns out, in the link the above, it was specified that "The crabgrass seeds germinate when the soil temperature at a depth of 4" stabilizes at 55Ã‚Â°F. This soil temperature can coincide with the time the forsythias are in bloom." Well, hey! THAT'S the temp that came with the seed potato instructions! So I've extrapolated it to mean that seed potatoes should be planted when forsythias are in bloom as well as "when the shadbush flowers." My 3 varieties of shadbush/Amelanchier have not bloomed yet, though they had budbreak a few days ago, so it's not long now.
As you implied, the trick, I think, is to adapt the Phenological signs to your own local micro-climate and varieties of plants. For instance, my own crocuses bloom much earlier than when the neighbors' forsythia are in bloom (I don't have one).
Daffodils have been in bloom. I have green ash, maple, and elm trees to keep an eye on, as well as bearded iris. Maybe I should plant some chokecerries. My only mature oak tree is a Willow oak, so no help there on size of squirrel ears. They say elsewhere to look to mature
trees rather than young "whipper snapper" trees because they haven't experienced the seasons for multiple number of years; so, they don't know any better.