Hello Jeff,

Thanks for reaching out!

It sounds like you also checked in with my friend Dan on a call to the lab, so I'll include his links here, but also something he thought of after you chatted!

So, first, when you get a chance, you'll probably want to get a soil test. Cucurbits (or Cucurbitaceae, if you want to really be a nerd about it) are pretty heavy feeders, so a slow-release fertilizer or compost are often a good idea. Here's some great info about that from Virginia Tech: https://www.pubs.ext.vt.edu/426/426-406/426-406.html

All of that said, Dan thought of something after your chat that I also believe is the main culprit here: cucumbers and melons are incredibly sensitive to soil temperature, and the ground is still quite cold for these plants. Generally, you want the soil (not the air) to be 65 degrees or above when planting nightshades such as tomatoes, peppers, and eggplants or cucurbits. Unless you're in a greenhouse, there's probably nowhere in Vermont that has hit these temperatures yet.

There's also an issue of damping off which occurs in soils that are cold, wet, and harbor potentially pathogenic organisms. You can learn about that here:  https://extension.umn.edu/solve-problem/how-prevent-seedling-damping

So my advice is to wait until the ground warms up a bit and try with another set of seedlings! Hope this helps!