I would not give up on them yet, however, my Hidcote Blue and Jean Davis are putting out new growth and I am much colder than you.

Brookston silty clay loam is the soil type. It is poorly draining and has a seasonal high watertable. Maybe if I replanted with peat moss I'd have a better chance? Should I make it a raised bed with peat moss while i'm at it?

Your plants need good drainage especially the Lavender. I would not add peat moss to the raised beds.

I agree - adding peat moss will do just the opposite of what you want. It will hold or retain moisture, not improve drainage. Lavender requires very lean, fast draining soil (even in winter) and lots of sun. Mediterranean plants of most types are just not well suited to most of the continental US, regardless of cold tolerance, which is also generally not very strong. If soils and climate not suitable, you may want to consider lavender as an annual planting.

poorly draining and has a seasonal high watertable. Maybe if I replanted with peat moss I'd have a better chance?

==>> as noted.. peat moss.. the sponge.. will hold more water ... ken

I also have another question. What should I do for my blueberry plants in this location? I planted them last year and they died and then planted more this spring hoping they would live if I added more soil acidifier, but I don't think that is going to be enough. Would moving them to a raised bed and a peat moss/compost mixture provide enough drainage? How deep do the raised beds need to be for blueberries? I could move them to another site with full sun that's on a gravel bed, but then their roots would stop there where the raised bed hit the ground.

For blueberries, get a soil test. No guessing.

My lavender hasn't done anything yet, so it is still too early. I'm thinking it doesn't start growing until May. Whenever it is, it is later than everything else, and the last to be cleaned up in that bed.

I'm glad others are experiencing the same thing. I planted some lavender last year and thought it might have died. The stems are there but nothing else. But they're slightly pliant so I thought maybe..... and just this morning I saw some green on a stem. Keep the faith, it may come back!

Even in my well-drained soil lavender has a difficult time with prolonged winter wet. The only way I've managed to keep it alive prior to this year is by growing it in a pot with sandy soil and then turning the pot on its side for the winter to keep out water but in a shady spot where the pot will be buried in snow for insulation.

Last season I planted 4 small Phenomenal in the ground, and they seem to have weathered the winter better than any other variety I have tried, and I think I have tried every variety that is supposed to be hardy in zone 5.

I read a while back that Munstead lavender is one of the hardiest, and this is what I planted in my NY zone 5 area. It never fails to winter over for me. I have it in a spot that gets full sun all day, in not overly rich soil. It seems to like it on the dry side. If conditions are right, its a great low maintenance plant. A big plus for me is that wildlife doesn't seem to eat it.

I am in Zone 6 New England and I have had good luck with the variety of lavender called Dilly Dilly. I bought it from the website "Accents For Home And Garden".