I keep my carrots right in my Zone-5b garden all winter. At the end of the gardening season each year, when the weather cools, I cover our carrot rows with 7 to 10 inches of straw mulch. The coverage needs to be thorough and extend a bit past the edges of the rows. I usually insert tall stakes at the head of each row so I can find them under the snow.
During the coldest months, I am able to go to the garden, brush off the snow layer, pull back the straw and dig the carrots easily. The ground under the straw doesn’t freeze, and the winter carrots are sweet and crisp.
I harvest the remaining carrots when I move the straw aside in the spring to begin preparing my garden. The spring carrots are the sweetest of all. The straw keeps the soil at a fairly constant temperature until the days get warm around the end of April.
This winter carrot harvest method is the lazy person’s root cellar, and it has worked well for me.