Crops grow when temparature is above zero, and grow twice as fast when it's above 28 degrees. It doesn't need at least 28 degrees, just anything above zero. A temperature above 28 simply speeds it up.
In Winter, temperatures hit zero degrees and below. Farms and harvestable plants (Saplings, Grass Tufts, Berry Bushes, etc..) will never regrow in Winter. Farms can't even be fertilized when the temperature is below 0, so no, they will never grow in Winter, not because of the lack of light, but the lack of heat.
See Also
Farm SoilAnd no, fires are not enough in Winter. However, it is possible to make crops grow through nights using a fire during other seasons.
