Hi, 

Oh no! We would suggest you wait and see. They might be able to send up new growth. The growth was probably just too new, and the rapid weather change, without having time to harden off to the cooler temps, must have gotten to them. Last night's cold was pretty low, depending on where you are in Baltimore County and if your veggie garden happens to be in a frost-prone pocket. Salad greens and other cool-season crops are likely ok, as you noticed.

Personally, I've had potatoes that I missed digging, and the tops died back with the heat, lay in the soil over winter, and came back the following spring, so they will likely come back with new growth. Just watch the weather, and if we have any hard frost warnings and they are newly emerged, you could cover them with a sheet, overturned pot or bucket, or a frost cloth to protect them.

Emily