January Treat weeds with herbicide as soon as they appear.  Don't let them flower and disperse their seed.  Protect frost-tender plants from freezing temperatures with frost cloth, bedsheets or newspaper.  Fertilize citrus in January or February with one-third of its total annual nitrogen requirements.  Prune established roses.  Prune non-native deciduous shade and fruit trees, and grapes.  Examine plants for aphids.  Spray them off regulary with a blast of water from the hose.