RpR said:Plants do not like massive temp changes especially when they are young.
They go into what I call shock. They may not die but will often just sit there doing nothing for an uncomfortable amount of time.
The fact yours have brown like that is not good, so you had best cover them at night.
When I have planted early spring , taking a gamble up here, often when we get twenty plus degrees temp. swings, day to night, I have had them sit for a month doing nothing, even when temps. rise but when I have seen brown like that, often they simply die, slowly.
One of he best ways to deal with cold like that , besides covering them is to water them heavily before sun down.
It is one of the ways we combat frost in the fall as the evaporating rising water keeps the plant warmer.