hi there wruwtrix

i wouldn't be overly worried...mother nature has a way of taking care of things like this...
the green plants might be biannuals which stay green over the winter..
.or if you have tulips and other spring bulbs...they will go back to sleep if things get cold...
if you have some tenders...yes you can cover them...
but i wouldn't worry...

cheers and good luck
diggy

I live in zone 3 in northern Ontario. Often when the snow goes my plants show green, and we get weather like much like yours. Today and the last week it has been 10C about 50F.

I know we are going to get colder weather before we can say spring has arrived. Most plants make it through these swings in weather if they are mulched.

If you do have the odd one where you have pushed the zone then something like a cardboard box over it at night will see it through. Don't cover with plastic because plastic conducts the cold, and be sure to take it off in the day so it can get the sun.

Also covering with leaves works well-I covered my ferns with leaves this winter and when I pulled them back a week or so ago they were still green!

Most plant that tend to come up early have an amazing tolerance to cold weather. I wouldn't be overly concerned about a warm stretch now as the soil is still quite cold and possibly frozen a little underneath. That helps prevent things from popping too early.