How cold is too cold to open up a hive and feed?

I’m in Louisville my area, 6a/b.  It has been very cold this year and I want to get in and feed the bees (I didn’t feed right before winter, just what they had, but didn’t harvest either)

I’m wondering how warm it needs to be to open up, put in feed and close?  I’m afraid if I don’t feed them they won’t make it. All three are first year hives, two in langstroth and 1 topbar. The topbar was a swarm from a friend.

It’s going to be in the mid to high 50s late this week, that warm enough?

I suppose that if it's in the 50s, that the bees will be flying, so that seems like warm enough to me. You might try lifting the closed hive. See how heavy it is. If it's full of honey still, no need to open it at all.

could also use a bottom feeder. if you're strong enough or you've got help, lift the whole works off the bottom board, add an empty body, put a feeder in, and move the hive back on top. they won't lose near much heat if you never take the lid off or break the hive apart.

1) Avoid syrup at this time of year. They need to be warm and active to dry it down.

2) Fondant or dry granulated sugar works well in winter. Personally I buy blocks of fondant that I wrap in clingflim and place directly on the frames with a slit cut into the plastic.

To give them dry sugar place a sheet of newspaper across the top of the frames - leave a small part uncovered for bee access. Damp it with a light spray of water. Pour the granulated sugar on top in a heap. Lightly spray the top of the sugar to make it moist. The damp will hold it all together in a clump.

3) Be sure that they actually need it. Don't open them to inspect, but you can heft the boxes to feel how heavy they are.

55 F is what I consider to be lowest temperature to open a hive.