January is the coldest month of the year, days are pleasant and night times are cool. It is a good idea to wrap trunks of young citrus with burlap to protect from frost. If leafage gets frost burn, leave dead foliage on to protect from further damage. Add a little compost and a thick layer of mulch to protect the tender new growth. If the ground is workable and not to wet, now is an excellent time to turn the soil. Not only will this expose insect eggs to the effects of winter and hungry birds, the cold will help to break apart heavy clods of dirt.
As an irrigation tip, keep above ground irrigation equipment such as garden hoses, irrigation valves and pipes insulated or covered to help protect from cracking due to cold exposure.