George wrote:

We get good germination
rates on pretty much everything, except peas. (Snow & Sugar Snap, if it
matters.) For those, we get maybe one in ten, at best. The few that do
germinate seem to grow OK.

Well, it it's any help, I planted Sugar Snaps on 5/6, and the second row on
5/13.... both germinated in about 10 days and are now just thinking about
climbing the baling twine macrame trellis I'm behind on stringing up (as
usual). I usually plant a bit earlier, but too early just has the seed rot
in the ground. They almost always germinate well here. I didn't plant
snow peas this spring, though they usually do about the same a Sugar Snap
peas. Perhaps too much moisture as well as too cool?

I'm zone 4/5, in the hills west of Schenectady, at 1400 feet elevation, so
probably comparable to your conditions. Oh yes, clay soil in between the
hunks of shale.
Gary Woods AKA K2AHC- PGP key on request, or at home.earthlink.net/~garygarlic
Zone 5/6 in upstate New York, 1420' elevation. NY WO G