Why is that? First, what is frost? Well, there are a few types, including frozen dew, but the most common is "hoar frost". "Depositional frost is also known as white frost or hoar frost.

The Victory Seeds website has a chart for probabilities of the last frost. By April 21, for instance, there’s a 20% chance the last 32-degree day has passed. By May 28, there’s a 90% chance there’s no ...

The interaction between the warmer wet air and the cold dry air just above it, can condense as hoar frost-like crystals on the ice surface. This process requires very little to no wind.