You should be fine. I have all my herbs in the garden already and they're look happy to be there. I think in our zone the damaging cold is pretty much behind us.

The average last frost date in my location is April 15. I usually find that it's a good idea to pay attention to those estimations. I've heard threats of 30s later this week!

lily, you should call your local extension office to find out when the "last expected frost date" is. It varies, of course, from one place to the other. They will know what you mean and have the information at hand.

So, what kinds of herbs did you get?

Here is a link that might be useful: Your extension contact information

Also it depend on the type of herbs. For example, Thyme, Oregano, sage, lavender, parsley, chives, cilantro can be transplanted withouth worrying about LFD. But Basils, summer savory, dills,..like somewhat warmer air and soil.

Zone 6 has your last frost date in May. Planting tender items outside before then is a gamble. I wait until May here in Western NY State.

I linked in a google search - pick the first choice for a lookup of your last frost date by zipcode.

FataMorgana

Here is a link that might be useful: Google - Last frost date by zip code

When we lived in Michigan they use to sell cold caps for those sudden cold nights. They were just pieces of cardboard tent shaped to cover for a little added protection which we took off during the day if the it warmed back up to a save temp. I would think even a cardboard box would do the job for shot periods of time if that was necessary. If there is a breeze then a rock on the top of the box should do the trick.