Good Morning Washingtonian! Coleus are great additions to any garden. As you already know, coleus are a tropical plant and really are drama queens when exposed to what they believe is inclement weather. There are a lot of factors in regards to how much cold they can take - have they been properly hardened off before these cold nights have set in, how long did it stay cold, humidity (dew point), maturity of the plant, etc. I have had similar issues with coleus in the past - they don't seem to want to come out of a cold injury fast, if at all.
Back to your question - how much cold? They really don't like even low 40's at night. (I tell mine that it doesn't freeze until 32 (plus or minus) so you'll be fine...but sometimes they disagree)
Good luck and enjoy your coleus!
