Sprouted ones need to be brought in or covered if in ground.

45 is the minimum recommended for seedlings, especially peppers, and if the air temp is 48 the ground level temp could easily be 45 or less.

Can you cover them with a blanket or such?

Dave

Digdirt, hit it. Plants vary.
I don't consider it "stunting". Plants will wait until the right temperature/light cycle to take off, as long as they are not damaged.
Or just search "cosmos cold tolerance" (example) for each of your plants. One site says cosmos will tolerate 35 degrees.
The link below doesn't really pertain, but you can find similar that might. A lot of studies have been produced on the matter.
Bob

Here is a link that might be useful: frost tolerance

Most plants are surprisingly hardy at the early stages as long as they are not left too cold for extended amounts of time. If you are worried about the temperature and already planted just cover the little guys with a sheet or some good plastic overnight. The weather should be warming up pretty fast, and if not just blame that darn groundhog!